Top 10 Cancer Fighting Supplements: Evidence Based Literature Review (2025)

Are you overwhelmed by conflicting advice on cancer, diet, and supplements? You’re not alone. With so many claims out there, it’s hard to separate fact from fiction.

Can certain foods lower your cancer risk? Are some foods increasing it without you realizing? What about vitamin and mineral supplements—do they help prevent cancer, or could they actually increase your risk?

The term "anti-cancer supplements" can be misleading. While some nutrients support the body in cancer prevention or treatment, others may interfere with therapies or even pose risks.

This guide compiles over 300 scientific references on cancer, diet, and supplements—helping you navigate the facts with confidence.

Understanding Supplements and Cancer: What You Should Know

• Dietary supplements are not regulated like medications. Unlike prescription drugs, supplements aren’t rigorously tested by the FDA for safety or effectiveness before hitting the market.
• Not all supplements are beneficial. While some may support health, others could interact with cancer treatments or cause unwanted side effects.
• Choosing the right supplement can be overwhelming. With thousands of options available, knowing where to start can be a challenge.

Should You Take Supplements During Cancer Treatment?

If you're considering supplements, always consult your doctor first—especially since some may interfere with medications or ongoing treatments.

How to Interpret Scientific Research

Not all studies carry the same weight. Here’s how research ranks in terms of credibility:

• Meta-analysis and systematic reviews – The highest level of evidence, as they analyze and combine data from multiple RCTs and studies to identify overall trends and draw more reliable conclusions.
• Randomized controlled trials (RCTs) – The gold standard, providing the strongest evidence.
• Small human studies – Can offer insights, but results are less reliable.
• Animal studies (mice/rat models) – A step closer to understanding effects in living organisms.
• Lab studies (cell cultures) – Useful for early discoveries but not directly applicable to humans.

Related: Hallmarks of Cancer: What You Need to Know

What This Article Covers

We’ll explore dietary supplements that may help prevent cancer or aid recovery during treatment, along with the latest research and studies. New findings emerge constantly, so staying informed is key.

Let’s dive into the science and separate the myths from the facts!

Contents:

•  Top 10 Cancer Fighting Supplements

1. Vitamin D3 and K2
2. Turmeric (Curcumin)
3. Fish Oil (Omega-3 Fatty Acids)
4. Vitamin C
5. Magnesium and Molecular Hydrogen
6. Green tea (EGCG)
7. Quercetin
8. Melatonin
9. Garlic (Allicin)
10. Probiotics and Microbiome

• 3 Supplements That May Increase Cancer Risk
• Nicotinamide riboside supplements and Cancer
• Conclusion

While many vitamins and minerals can benefit your general health, there’s a huge market of unregulated supplements that may provide no added benefit to your health. Certain supplements even have the potential to negatively impact cancer treatments. This is because some supplements can counteract medications or medical therapies. If you’re thinking about supplementing your diet with anti-cancer vitamins, always talk to your doctor first.

Credit: FLCCC Alliance

We have organised and summarised relevant and salient research information in one place. Below, we look at the most published and studied categories.

Here is the list (listed in order of importance):

1. Vitamin D3 and K2

Is vitamin D the most powerful anti cancer supplement? Vitamin D can absorb calcium and help the immune, muscle, and nervous systems function properly. There are more than 12,000 search results on vitamin D and cancer on PubMed. 

A comprehensive analysis published in the journal Nutrients in April 2025 has discovered a fascinating but substantial link between vitamin D and colorectal cancer (CRC). The researchers reviewed and analyzed data from 50 separate studies involving over 1.3 million participants to determine how much vitamin D impacts your risk of developing colorectal cancer.

• This large-scale review looked at diverse populations — The data covered various groups and nationalities, including women in the U.S. Midwest, Danish adults with a family history of cancer and Canadians living in high-altitude areas. The participants had different health statuses as well — some had colorectal cancer, or a documented vitamin D deficiency. Others were also given a vitamin D supplement.
• While the participants varied in health status and genetic risk, a consistent pattern emerged — The researchers found that the lower your vitamin D levels, the higher your risk of developing colon cancer. On the flip side, people with adequate or optimal levels of vitamin D had dramatically lower rates of cancer.
• Unfortunately, majority of people today have very low levels of this vital nutrient — A recent study that looked at the vitamin D status of more than 5,600 adults found that 37.6% had vitamin D insufficiency (blood levels between 20 and 30 ng/mL), while 42% were severely deficient (blood levels lower than 20 ng/mL) in this nutrient.

This new research makes it clear that if you're not paying attention to your vitamin D status, you're missing out on one of the simplest and most powerful tools available to reduce your risk of colon cancer. Below are some of the compelling findings from the featured analysis that point to vitamin D as a key factor in reducing your risk of colorectal cancer.

• A landmark 1996 study found that women with the highest vitamin D intake had a 58% lower risk than those with the lowest intake.
• A 2021 meta-analysis found a 39% lower risk of colorectal cancer in people with higher blood levels of vitamin D. The researchers also noted that when vitamin D levels were monitored over time, those who maintained higher levels had a 20% lower chance of developing colorectal cancer down the line.
• A Canadian study found that supplementing with vitamin D reduced the incidence of precancerous polyps — by 33% for all polyps and 43% for high-risk ones. These polyps often go on to become cancer if not addressed early, so this kind of intervention has massive implications.
• The Iowa Women's Health study found that women who took vitamin D with calcium saw a 15% drop in colorectal cancer risk compared to those who didn't take any supplements.
• The Danish "Diet, Cancer and Health" study (one of the major ones included) found that vitamin D offered even stronger protection in people with a high genetic risk of colon cancer. That means if you've got a family history of this disease, optimizing your vitamin D status isn't just helpful — it could be life-saving.

Another 2023 systematic review and meta-analysis of 14 RCTs (randomized controlled trials), published in Ageing Research Reviews (Kuznia 2023) found vitamin D3 supplementation reduced cancer mortality by 6%. This wasn’t considered statistically significant, but when only studies involving daily vitamin D intake were analyzed, cancer mortality dropped by a significant 12%.

In another 2023 meta-analysis, 116 randomised controlled trials (RCTs) were analysed. The meta-analysis concluded that vitamin D reduces lung cancer mortality. 

*Note: "Death from anything" may be a clearer term for the layperson as opposed to 'All-cause mortality'. This is one of the best measures for the factors that increase the risk of what eventually and most likely will take someone's life.

The first randomized-controlled trial (DO-HEALTH) trial to investigate the combination of three complementary treatments for the prevention of cancer and suggest that the combination of daily vitamin D3, supplemental marine omega-3s, and a simple home exercise program may be effective in the prevention of invasive cancer among generally healthy and active adults aged 70 and older.

Findings from a 3 year Randomized Controlled Trial with more than 2,000 participants observed a 61% reduction in the risk of invasive cancer among patients who completed a home exercise program and took vitamin D3 and omega-3 fatty acids daily. These results, from the DO-HEALTH trial, were published in Frontiers in Aging 2022.

 

A number of epidemiologic studies have also investigated whether people with higher vitamin D intakes or higher blood levels of vitamin D have lower risks of specific cancers. The results of these studies have been inconsistent, possibly because of the challenges in carrying out such studies. For example, dietary studies do not account for vitamin D made in the skin from sunlight exposure, and the level of vitamin D measured in the blood at a single point in time (as in most studies) may not reflect a person’s true vitamin D status. Also, it is possible that people with higher vitamin D intakes or blood levels are more likely to have other healthy behaviors. It may be one of these other behaviors, rather than vitamin D intake, that influences cancer risk.

The cancers for which the most human data are available are colorectal, breast, prostate, and pancreatic cancer. Numerous epidemiologic studies have shown that higher intake or blood levels of vitamin D are associated with a reduced risk of colorectal cancer (R). In contrast, the Women’s Health Initiative randomized trial found that healthy women who took vitamin D and calcium supplements for an average of 7 years did not have a reduced incidence of colorectal cancer (NEJM 2006). Some scientists have pointed out that the relatively low level of vitamin D supplementation (10 μg, or 400 IU, once a day), the ability of participants to take additional vitamin D on their own, and the short duration of participant follow-up in this trial might explain why no reduction in colorectal cancer risk was found. 

According to BreastCancer.org, research suggests that certain cancers such as breast cancer, can have a higher risk of occurring when the body has low levels of vitamin D.

Studies also show a link between vitamin D deficiency and cardiovascular disease, diabetes, and cancer (Sizar, 2020).

In 2016, a landmark study published in PLOS ONE found that women over 55 with blood concentrations of vitamin D higher than 40 ng/ml, had a 67% lower risk of cancer compared women with levels lower than 20 ng/ml.

 

Many experts now recommend 800 to 1,000 IU a day, a goal that's nearly impossible to attain without taking a supplement. 

Although the role of vitamin D in cancer prevention remains an area of research interest and debate, avoiding deficient levels is recommended. (American Cancer Society 2020)

Vitamin D can also be absorbed through sunlight, or with the following diet: 

• fatty fish 
• egg yolks 
• fortified milk

The Optimal Vitamin D Level for Cancer Prevention

Research has shown that once you reach a minimum serum vitamin D level of 40 ng/mL (100 nmol/L), your risk for cancer diminishes by a whopping 67%, compared to having a level of 20 ng/mL or less. 

Make sure to take 500 mg to 1000 mg of magnesium and 150 mcg of vitamin K2, (not K1) which are important cofactors for optimizing vitamin D function. And, remember the only way you know what your vitamin D level is, is to test it. Vitamin D level should be in a therapeutic range of 50 to 70 ng/ml for treatment of rheumatoid arthritis. Most people are shocked how low their level is when they finally get around to testing it.

You'll also want to ensure you're following an overall healthy lifestyle to reduce your cancer risk as much as possible. 

Recommendation: Target a Vitamin D level of 50-70 ng/mL. 

Caution: The dosage for vitamin D in prevention (1,000 to 2,000 IU daily) is very much different from the high dose treatment dosage i.e. 20,000 to 50,000 IU daily. Always consult your doctor first! 

Related: Vitamin D Level and Cancer: Vitamin D Reduces Cancer Deaths

Vitamin K2: A wonder nutrient against cancer

A large German study of 24,340 adults ages 35 to 64 showed that the quartile (one-fourth of the participants) consuming the most vitamin K2 were 28 percent less like to die from colon, breast, prostate, or lung cancers than those in the lowest quartile of consumption. (This was after factoring in things like age, weight, exercise, and the like.)

The connection was strongest for lung and prostate cancers.

There’s more: A study published in the International Journal of Oncology found that cancer cells grow more slowly in lung cancer patients treated with vitamin K2.

A previous study found the same effect with leukemia patients. Vitamin K2 also safely suppressed growth of hepatocellular carcinoma, a common and deadly type of liver cancer, by blocking cell replication and triggering apoptosis. (source)

Related: Vitamin K1 vs K2

Vitamin K also slashed the risk of liver cancer coming back, in a group of patients who had experienced remission. Here’s the story. . .

Sixty-one liver cancer patients were declared free of cancer following surgery. Thirty-two of them received a vitamin K2 analogue, whereas 29 received placebos. The cumulative survival rates for the patients who received menatetrenone were 100% at 12 months, 96.6% at 24 months, and 87.0% at 36 months; and the corresponding survival rates for patients in the control group were 96.4%, 80.9%, and 64.0%, respectively (P = 0.051). (source)

A disorder previously nicknamed “pre-leukemia” called Myelodysplastic syndrome (MDS) often leads to full-blown leukemia, with all its disastrous consequences. In MDS, the bone marrow churns out young white blood cells instead of mature ones. But vitamin K treatment can induce apoptosis, and cause MDS cells to differentiate into healthy, mature white blood cells that can help your immune response, even in the face of full-blown leukemia. (source)

Vitamin K2 combined with vitamin D3 may be even better. In a recent study, it more than doubled the response rate of patients with low white blood counts, boosting it from 13 percent to 30 percent.

Vitamin K may also help against non-Hodgkin lymphoma, stomach, nasopharynx, and oral cancers. (source)

Caution: Vitamin K2 can interfere with blood thinners, so discuss K2 with your doctor if you’re taking these medications. If you’re pregnant or nursing, stay below the RDA for K2 (65 mcg).

Buying Guide: Most vitamin D3 supplements include vitamin K2. Click here to buy vitamin D3 and K2.

2. Turmeric (Curcumin)

Curcumin is one of the nutrients with the most evidence-based literature supporting its use against cancer. There are more than 7,000 search results on curcumin and cancer on PubMed and more than 50 clinical trials with curcumin, most of which are still ongoing. The spice turmeric can be extremely helpful when it comes to fighting cancer. 

Interestingly, curcumin appears to be universally useful for just about every type of cancer (Arslan 2022), which is really odd since cancer consists of a wide variety of different molecular pathologies.

Studies show that the curcumin in turmeric may kill cancer cells and slow tumor growth. This preclinical research has taken curcumin from the lab to the clinic. 

The benefits of curcumin may include: 

• blocking cancer cells from multiplying
• killing colon, breast, prostate, and melanoma cancer cells
• slowing tumor growth

A review paper published in 2022, analysed 21 human studies. Sixteen out of 21 clinical trials were associated with the effectiveness of curcumin or turmeric on various types of cancer, and the other five clinical trials were related to the evaluation of the efficacy of curcumin or turmeric in relieving the side effects of cancer chemotherapy and radiotherapy. The emerging data from the clinical trials confirm that curcumin has the potential for cancer prevention and intervention. 

Both curcuminoids and related turmeric products have been sanctioned by the U.S. Food and Drug Administration (FDA) as safe.

Why Whole Turmeric Is Ineffective

Unfortunately, while there's some curcumin in whole turmeric, there's not enough in the regular spice to achieve clinically relevant results. The turmeric root itself contains only about 3% curcumin concentration. Another major limitation of curcumin as a therapeutic agent is that it is poorly absorbed. When taken in its raw form, you're only absorbing about 1% of the available curcumin.

Because it's not easily absorbed through your gastrointestinal tract, it's more effective to use a high-quality bioavailable curcumin extract, according to a 2013 study. A typical anticancer dose is just under 1 teaspoon of curcumin extract three or four times daily.

However, in the case of colon cancer, this poor absorption into the bloodstream may be an advantage. As there is poor absorption, higher levels of curcumin stay in the intestinal tract for longer periods of time, having an effect on gastrointestinal cancers. 

In one study, participants took a 1,080 milligram (mg) dose per day of curcumin for 10 to 30 days between their initial biopsy and surgical removal. The patients taking the supplement experienced a reduction in blood levels of inflammatory agent, improvement in their body weight and an increased number of dying tumor cells.

In a 2016 study, a team of scientists at the University of Pittsburgh and at Pondicherry University, India, discovered the bioactive ingredient in turmeric, curcumin, can both prevent and cure bowel cancers. The team found the compound triggered cancer cell death by increasing a level of protein labeled GADD45a. Lead author Rajasekaran Baskaran, Ph.D., who has more than 20 years of experience in cancer research, commented:

"Studies on the effect of curcumin on cancer and normal cells will be useful for the ongoing preclinical and clinical investigations on this potential chemo-preventive agent."

New Curcumin Forms

Convenience and efficiency has driven many of the changes in the forms of curcumin in later years. Because it's a fat-loving or lipophilic molecule, many newer preparations now include some sort of oil or fat, which improves its absorbability and bioavailability. Such preparations typically have seven to eight times higher absorption than the raw, unprocessed 95% concentration of dry powder. There are also newer sustained release preparations.

Turmeric and black pepper each have health benefits, due to the compounds curcumin and piperine. As piperine enhances curcumin absorption in the body by up to 2,000%, combining the spices magnifies their effects. (Healthline)

Buying Guide: Click here to buy Bioavailable Curcumin

  

3. Fish Oil (Omega-3 Fatty Acids)

PubMed has indexed more than 3,000 research studies on Omega-3 and cancer. Most people use fish oil supplements to enhance the amount of omega-3’s in their diet. 

The first randomized-controlled trial to investigate the combination of three complementary treatments for the prevention of cancer and suggest that the combination of daily vitamin D3, supplemental marine omega-3s, and a simple home exercise program may be effective in the prevention of invasive cancer among generally healthy and active adults aged 70 and older.

Findings from a 3 year Randomized Controlled Trial with more than 2,000 participants observed a 61% reduction in the risk of invasive cancer among patients who completed a home exercise program and took vitamin D3 and omega-3 fatty acids daily.

These results, from the DO-HEALTH trial (ClinicalTrials.gov identifier NCT01745263), were published in Frontiers in Aging 2022.

Findings from a study performed in mice, research from Harvard Medical School’s Beth Israel Deaconess Medical Center in Boston demonstrated omega-3 fat could reduce tumor growth by 67% (R).

The research was presented April 4, 2022 at the annual Experimental Biology meeting in Philadelphia. The animal model showed that omega-3 fatty acids helped promote the cancer-fighting activities of immunotherapy and anti-inflammatory therapy.

 

Many governments recommend eating omega-3 containing fatty fish, two times per week. But that is often not enough. Ideally, people would need to eat fatty fish four times per week, while also supplementing with omega-3 fatty acids, at least 1,000 mg of pure omega-3 (DHA and EPA) per day.

However, fish oil was shown in one study on mice (2015)Trusted Source to possibly reduce the effectiveness of chemotherapy, and for that reason ground flax seed is a worthy alternative.

Flax seed is rich in omega-3 fatty acids, which may reduce the risk of certain cancers. When supplementing, try to avoid flaxseed oil because it lacks the nutrients of ground flax seed. Ground flax seed can be purchased online or found in many larger grocery store chains. Simply sprinkle some ground flax seed on your food and enjoy.

Make sure you buy high-quality omega-3 fatty acid supplements, meaning that the omega-3 fatty acids are pure and have not oxidized much (having low “TOTOX” value).

TOTOX value stands for total oxidation value. The omega 3 fatty acids EPA and DHA from fish oil are highly sensitive to oxidation. This means that they are rapidly affected by contact with oxygen. Oxidised fatty acids are not beneficial to our health. For this reason, a good fish oil supplement has a low TOTOX value. The maximum TOTOX value is set at 26 by the Global Organization for EPA and DHA omega-3.

Buying Guide: Click here to buy Omega-3.

4. Green Tea (EGCG)

PubMed has indexed more than 2,000 research studies on EGCG and cancer.

The Minnesota Green Tea Trial (MGTT. 2015) is the largest and longest double-blind, placebo-controlled, randomized intervention study that specifically evaluated the effects of oral GTE (green tea extract) containing defined quantities of EGCG on established biomarkers of breast cancer risk.

They randomized and stratified 1075 healthy postmenopausal women at high risk of breast cancer according to their breast tissue density and catechol-O-methyltransferase genotypes and divided them into two groups: 537 placebo and 538 green tea groups. Green tea group participants took 4 capsules that contained 843 mg EGCG, whereas the placebo group took capsules without green tea extracts.

Researchers measured changes in percent mammographic density, circulating endogenous sex hormones, and proteins of the insulin-like growth factor axis. Their results showed that supplementation with green tea extract could modify and reduce mammographic density (MD) and protect against breast cancer, even though it was only significant in younger women (50–55 years) and had no effect in older women (R), an age-dependent effect similar to those of tamoxifen.

According to a 2018 review, EGCG and green tea extracts may help prevent or delay cancer onset, cancer recurrence, and secondary growths from cancer.

However, the National Center for Complementary and Integrative Health (NCCIH) state that studies of green tea and cancer in humans have so far produced inconsistent results.

Several epidemiological studies (2011) have reported that the consumption of green tea may decrease cancer risk. Studies have also confirmed numerous health benefits of green tea including prevention of cancer (R, R) and cardiovascular disease, as well as anti-inflammatory, antioxidant, antiarthritic, antibacterial, and antiviral effects. (R, R, R, R).

Green tea also contains chemicals called polyphenols that have antioxidant, anti-inflammatory properties and anti-angiogenic properties, and the catechins in green tea polyphenols show very strong anti-angiogenic properties.

If you have cancer, consider drinking up to 3 cups of green tea per day to experience the benefits. Green tea pills are also available, but may be too concentrated.

Some studies show health benefits in people who drink as little as one cup per day, while other studies deem five or more cups per day to be optimal (Source, Source).

5. Vitamin C

PubMed has indexed more than 3,000 research studies on vitamin C and cancer and more than 5,000 studies on vitamin E and cancer. United States Preventive Services Task Force has recommended the use of Vitamin C and E supplementation for cancer prevention (R).

Prevention

2022 - An umbrella review* (Xu 2022) to assess the existing systematic reviews and meta-analyses for the association between vitamin C intake and multiple health outcomes; showed that vitamin C intake was associated with reduced risk of all-cause mortality, cardiovascular disease (CVD), oesophageal cancer, gastric cancer, cervical cancer and lung cancer with an increment of 50–100 mg per day.

Beneficial associations were also identified for respiratory, neurological, ophthalmologic, musculoskeletal, renal and dental outcomes. A total of 76 meta-analyses (51 papers) of randomised controlled trials and observational studies with 63 unique health outcomes were identified. Harmful associations were found for breast cancer and kidney stones for vitamin C supplement intake. 

*Umbrella review: An umbrella review, or a review of reviews, is a systematic review that only considers other systematic reviews as an eligible study type for inclusion.

2022 - Obese women who took vitamin C and B6 at amounts that exceeded the recommended daily intake levels were associated with a lower risk of breast cancer, according to a five-year long South Korean cohort study. 40,432 women without a history of cancer at baseline were included in this study.

2022 - A meta-analysis to review the association between vitamins and brain cancer showed that intake of vitamin C, β-carotene, and folate can reduce the risk of brain cancer, while high serum α-tocopherol (vitamin E) concentration also has a protective effect on brain cancer.

A 2017 meta-analysis of 11 studies concluded that patients with lower concentrations of serum vitamin E (the vitamin E level in your blood) had a higher risk for colorectal cancer.

Treatment

2023 - A systematic review to evaluate the existing literature on the safety and efficacy of vitamin C, E and selenium supplementation in oncology patients. Findings were generally favorable among the studies, and adverse effects of supplementation were limited. The review concluded that antioxidant supplements may provide benefits in reducing incidence or severity of treatment-induced side effects with limited risk for adverse effects.

2022 - A systematic review on the effect of vitamins C and E on cancer survival showed improvement of survival and progression rates of cancers by vitamins C and E. However, the authors concluded that more high quality trials with large sample sizes are required to confirm.

Vitamin C is known as an antioxidant, but at high concentrations, vitamin C can kill cancer cells through a pro-oxidant property (Transl Oncol. 2020). This study has also demonstrated that vitamin C treatment with magnesium supplementation provided more effective anticancer therapy than vitamin C treatment alone.

High-dose vitamin C cancer therapy was introduced by Linus Pauling and Ewan Cameron [R]. Clinical demonstration results by Pauling and Cameron showed that intravenous injection of 10 g/day of vitamin C extended the survival time of terminal cancer patients by about 4.2 times. However, results from the Mayo Clinic in 1979 showed that the survival time of vitamin C–treated patients was even shorter than that of the placebo group patients [R]. A significant difference between those two research groups was the route of AA administration: intravenous injection and oral administration, respectively. 

To understand the mechanism of AA's anticancer activity, many research groups have treated colon, prostate, leukemia, lymphoma, brain, and stomach cancer cells and chemically or genetically transformed cancer cells with AA and showed cancer growth inhibition and even cancer cell death through hydrogen peroxide–mediated reactive oxygen species (ROS) generation [R]. In most cases, the pharmacological concentration of vitamin C required for anticancer effects (EC50 value of 1–10 mM) could only be achieved by intravenous administration. Thus, to apply vitamin C as an anticancer therapy, a high intracellular concentration in cancer cells is critically important (R).

According to the Mayo Clinic (2023):

"More recently, vitamin C given through a vein (intravenously) has been found to have different effects than vitamin C taken in pill form. This has prompted renewed interest in the use of vitamin C as a cancer treatment.

There's still no evidence that vitamin C alone can cure cancer, but researchers are studying whether it might boost the effectiveness of other cancer treatments, such as chemotherapy and radiation therapy, or reduce treatment side effects.

There are still no large, controlled clinical trials that have shown a substantial effect of vitamin C on cancer, but some preliminary studies do suggest there may be a benefit to combining standard treatments with high-dose IV vitamin C."

 

According to the concluding remarks from a 2020 article from the National Cancer Institute:

Vitamin C as a cancer therapy has had a controversial past. What has been intriguing are small clinical trials that suggest some responses, but with no clear rationale for why cancers should respond to vitamin C or a path forward for explaining which patients are most likely to respond. Now a growing number of preclinical studies are showing how high-dose vitamin C might benefit cancer patients. Importantly, these preclinical studies provide a clear rationale and potential biomarkers that may help personalize the therapeutic approach and identify patient populations that are likely to respond to high-dose vitamin C therapy. Since the mechanisms of action of vitamin C are becoming better defined, we can propose vitamin C combinations in a more rational, hypothesis-driven manner. In addition, given the current high financial cost of new cancer drugs, it seems rational to improve the effectiveness of current therapies by studying their clinical interactions with vitamin C. In our view, the implementation of this treatment paradigm could provide benefit to many cancer patients.

Related: Benefits of Vitamin C in Cancer Treatment

Buying Guide: Click here to buy vitamin C and quercetin

6. Magnesium and Molecular Hydrogen

PubMed has indexed more than 5,000 research studies on magnesium and cancer.

Magnesium and Colorectal Cancer

Several studies have demonstrated an association between high magnesium intake and reduced risk of colorectal cancer (CRC).

An analysis of the prospective, Swedish Mammography Cohort (JAMA 2005), evaluated 61,433 women aged 40 to 75 without a history of cancer for a mean follow-up of 14.8 years. The highest quintile of magnesium intake was associated with a significantly lower risk of CRC compared with the lowest quintile. This benefit was observed for both colon and rectal cancers.

A case-control study evaluated 2204 subjects from the Tennessee Colorectal Polyp Study (2007), which demonstrated that increasing total magnesium intake was significantly associated with decreasing risk of CR.. The highest tertile of dietary magnesium intake (>298 mg/day) was significantly associated with reduced risk of CRC in an age-adjusted model.

A study of 140,601 postmenopausal women from the Women’s Health Initiative (2015) with an mean follow-up of 13 years demonstrated a significant reduction in CRC risk with the highest quintile of total magnesium intake compared with the lowest quintile of magnesium intake. The benefit was driven by colon cancer, with a trend for rectal cancer.

Magnesium and Pancreatic Cancer

A study of 66,806 subjects aged 50 to 76 at baseline from the Vitamins and Lifestyle cohort (Nature 2015) evaluated magnesium intake and the incidence of pancreatic cancer during a mean follow-up of 6.8 years. Subjects with magnesium intake below the recommended dietary allowance were more likely to develop pancreatic cancer, particularly in those whose intake was less than 75% of the recommended dietary allowance. In this study, a 100 mg/day decrease in magnesium intake resulted in a 24% increase in risk of pancreatic cancer.

Magnesium and Vitamin C

A 2020 study demonstrated that vitamin C treatment with magnesium supplementation provided more effective anticancer therapy than vitamin C treatment alone.

Molecular Hydrogen and Cancer

There is little evidence to show that molecular hydrogen can reduce the risk of cancer. 

However, in terms of cancer treatment, studies involving the effects of H2 on cancer were systematically reviewed. More than 600 articles related to molecular hydrogen and cancer were retrieved from Cochrane, PubMed and Google Scholar, and 27 articles were included for this systematic review (2023). 

Based on the authors' analysis, "H2 plays a promising therapeutic role as an independent therapy as well as an adjuvant in combination therapy, resulting in an overall improvement in survivability, quality of life, blood parameters, and tumour reduction."

Although H2 has demonstrated significant anti-cancer effects, the underlying mechanisms have not yet been elucidated. Many studies have shown that H2 therapy can reduce oxidative stress. This, however, contradicts radiation therapy and chemotherapy, in which ROS (Reactive Oxygen Species) are required to induce apoptosis and combat cancer. 

A 2020 study in Japan administered hydrogen therapy to 42 patients with stage-four lung cancer. The researchers found that hydrogen therapy could extend the overall survival of the patients. Specifically, patients receiving hydrogen therapy had a median survival time of 28 months, almost triple the survival time of those undergoing immunotherapy.

Buying Guide: Best Molecular Hydrogen Tablets

Note: Most Molecular Hydrogen tablets uses pure elemental magnesium as its carrier and provides you with approximately 80 mg of magnesium per tablet. So, you receive also highly bioavailable magnesium for a healthy brain, muscles, cells, kidneys, and heart.

7. Melatonin

PubMed has indexed more than 3,300 research studies on melatonin and cancer.

Melatonin is one of the most important antioxidant molecules. In the human body — aside from having direct antioxidant effects — it also stimulates the synthesis of glutathione and other important antioxidants like superoxide dismutase and catalase.

Many people are not aware that only 5% of your body’s melatonin — which is also a potent anticancer agent — is produced in your pineal gland. The other 95% is produced inside your mitochondria — provided you get sufficient near infrared exposure which is typically from sun on your bare skin. This is why vitamin D is more than likely a biomarker for sun exposure, which is intricately involved in melatonin production. (R)

The Mediterranean Diet (MD) dietary pattern is also rich in antioxidants, such as melatonin. A systematic review published in Antioxidants (Elena 2023) showed high melatonin contents in MD-related foods, such as tomatoes, olive oil, red wine, beer, nuts, and vegetables. The consumption of specific MD foods increases melatonin levels and improves the antioxidant status in plasma.

Melatonin is also known to play a fundamental role in regulating the sleep-wake rhythm; however, in the last 10 years it has been discovered that it is actually involved in many other biological mechanisms, also playing an important role in the inflammatory, metabolic and neoplastic processes. In fact, the mechanisms by which melatonin performs an anti-tumor effect are many: it has an anti-oxidant effect that protects against DNA damage, acts as a scavenger of reactive oxygen species (which undermine genomic stability), stimulates DNA repair mechanisms, improves the functioning of the mitochondrial respiratory chain, and inhibits mitochondrial mitophagy and telomerase activity (Molecules 2018).

In addition, melatonin increases the expression of the p53 protein, induces its phosphorylation, inhibiting cell proliferation, promotes apoptosis, reduces the levels of the vascular endothelial growth factor and endothelin-1, fundamental for tumor growth and metastasis formation, reduces inflammatory processes and cell migration (Molecules 2018).

Reduction of melatonin production has also been seen in some types of cancer (breast and prostate) (Mogavero 2021).

Melatonin - Treatment

2022 - An umbrella review of meta-analyses based on randomized controlled trials (Pharmacological Research 2022):

"Survival at one year (P < 0.005) significantly increased with cancer patients."

2020 - A case series of 14 advanced cancer patients (Trends in Oncology 2020), treated with high dose (1,000 mg/day) of melatonin; achieved a disease control of 54% of the patients:

"Moreover, this preliminary study may also suggest that high dose melatonin has no toxicity in cancer patients with poor clinical status, as well as in healthy subjects."

2005 - A systematic review of 10 randomized controlled trials (J Pineal Res 2005):

"All trials included solid tumor cancers. All trials were conducted at the same hospital network, and were unblinded. Melatonin reduced the risk of death at 1 yr (relative risk: 0.66). Effects were consistent across melatonin dose, and type of cancer. No severe adverse events were reported. The substantial reduction in risk of death, low adverse events reported and low costs related to this intervention suggest great potential for melatonin in treating cancer."

Related: What You Need to Know About Melatonin

8. Quercetin

PubMed has indexed more than 4,000 research studies on quercetin and cancer.

2022 - A paper published in August 2022 in Nutrition Research analyzed the pro-apoptotic effect that quercetin has on aging cells. The paper reviewed preclinical and early phase data using quercetin as a senolytic agent and found the data showed it was effective in “preventing or alleviating cancer formation.”

The authors reviewed the importance of cellular aging in the development of cancer cells and the effect that quercetin may have on the suppression of cancer cell proliferation. 

Cellular senescence is a dynamic and multi-step process that is associated with alterations in metabolic activity and gene expression. This can compromise tissue regeneration and contribute to aging. On the other hand, by removing senescent cells, age-related dysfunction can be attenuated and potentially extend the lifespan.

2020 - Another paper (2020) identified some of the anti-inflammatory, antioxidant and antiproliferative properties quercetin has that enhances breast cancer treatment, while another (2020) evaluated its effect on the treatment of ovarian cancer, which is a serious cancer growth and threat to women's health.

2019 - Research also has demonstrated that quercetin can promote the loss of cell viability and autophagy through several pathways, including those involving mitochondrial function and glucose metabolism.

This study published in 2017 in Oncology Reports took things a step further, finding that quercetin induced cancer cell death in nine types of cancer, including prostate cancer, colon cancer, and breast caner.

Quercetin affects endothelial (thin membrane lining heart and blood vessels) cell proliferation, migration, and angiogenesis. As an anti-angiogenic compound, it has been shown to have a targeted effect on tumor angiogenesis in both in vitro and in vivo experiments. It has also been demonstrated in animal experiments that quercetin can reduce angiogenesis.

In another 2017 study, researchers gave quercetin to mice with tumors. Researchers found that mice in the quercetin-treated group showed delayed tumor growth, no significant changes in daily behavior, significantly better survival ratings, and increased rates of cell death.

Quercetin may also target bladder cancer. In 2016, researchers published a landmark study in the American Journal of Cancer Research. Researchers analyzed quercetin’s effect on cancer cells in a test tube. They concluded, “We are the first to show that quercetin displays potent inhibition on bladder cancer cells via activation of AMPK pathway.”

According to Mount Sinai, quercetin should be used with caution as it may interact with certain antibiotics by reducing the effectiveness of the drug. It may also enhance the effect of some blood thinners, which can increase your risk of bleeding. In addition to these, it may interact with corticosteroids, digoxin, cyclosporine and fluoroquinolones.

Buying Guide: Click here to buy vitamin C and quercetin

9. Garlic (Allicin) and Onion

PubMed has indexed more than 1,200 research studies on garlic and cancer. Garlic and onions belong to the Allium genus of plants.

2023 - A randomized controlled trial (RCT) on garlic and gastric cancer (GC), published in January 2023, found a significant reduction in the risk of developing GC with increasing dietary intake of allium vegetables, particularly garlic vegetables. 

The study was conducted on the basis of the Shandong Intervention Trial, a randomized, placebo-controlled, factorial-designed trial (1995-2003) in a well-recognized high-risk area for GC in China. Participants were continuously followed up to December 2017 for 22.3 y (1995-2017). A total of 3,229 subjects were included.

2020 - A meta-analysis of 11 studies, published in January 2020, did find evidence that garlic could reduce the risk of ColoRectal Cancer. 

Another study published in the Asia Pacific Journal of Clinical Oncology (2019) revealed the odds of getting ColoRectal Cancer were 79% lower in those who a diet high in allium vegetables, which include garlic, leeks and onions.

One study of 543,220 participants found that those who ate lots of Allium vegetables, such as garlic, onions, leeks and shallots, had a lower risk of stomach cancer than those who rarely consumed them (Source).

A study of 471 men showed that a higher intake of garlic was associated with a reduced risk of prostate cancer (Source).

Based on these findings, including 2–5 grams (approximately one clove) of fresh garlic into your diet per day can help you take advantage of its health-promoting properties.

Garlic is a great choice when it comes to giving your body a little extra protection. To reap the benefits of garlic, you should eat one clove per day, or 300 to 1,000 milligrams (mg)Trusted Source of garlic extract.

The active component in garlic is allicin, a compound that has been shown to kill off cancer cells in multiple test-tube studies (Source, Source, Source).

There is evidence demonstrating garlic can kill cancer cells in vitro. Several studies have analyzed the effects that dietary garlic may have on the development of colorectal cancer. 

Several clinical studies have found an association between garlic intake and a lower risk of certain types of cancer.

Despite the promising results showing an association between garlic and a reduced risk of cancer, more studies are needed to examine whether other factors play a role.

Related: Garlic, the ‘King of Cancer Prevention’

10. Probiotics and Microbiome

Researchers have also explored the influence of gut bacteria on cancer patients' responses to checkpoint inhibitors — a class of immunotherapy drugs that work by triggering your immune system to attack cancer cells. However, this treatment has a fairly low success rate. Only 20% to 40% of patients respond to the treatment, and researchers began suspecting the gut microbiome might be the key to success or failure.

Indeed, as reported in Nature, a 2015 study found that while microbe-free mice failed to respond to treatment with checkpoint inhibitors, mice given Bacteroides fragilis fared much better. Other researchers have had similar findings, showing Bifidobacterium improves the effectiveness of cancer immunotherapy in lab animals — again by triggering a more robust response by specific anticancer immune cells.

As you might expect, antibiotic treatment has been found to worsen response to immunotherapy, likely because antibiotics indiscriminately kill all gut bacteria, thereby ridding your body of many really important immune helpers. Importantly, even cancer therapies that do not rely on the activation of your immune response typically fail unless you have the appropriate gut microbes. (source)

For example, certain chemotherapy agents actually rely on gut microbes to eradicate the tumor directly. In other instances, the microbes' influence on cancer is related to their ability to influence gene expression alter the stability of your genes.

Read More: Gut Microbiome May Be a Game Changer for Cancer Prevention
 

Avoid Taking These 3 Supplements Too Casually as They May Increase Cancer Risk

Beta-Carotene

A meta-analysis published in Nutrition Reviews in 2023 analyzed eight randomized controlled trials and found that taking beta-carotene supplements showed no overall beneficial or harmful effects on cancer incidence but may increase lung cancer risk, particularly among smokers. Therefore, beta-carotene supplementation is not recommended for cancer prevention.

Additionally, a systematic review and meta-analysis published in Nutrients in 2022 established a 16 percent increase in lung cancer risk associated with beta-carotene supplementation, with smokers and asbestos workers facing an even greater risk of 21 percent.

A 2020 review study published in Antioxidants proposed that beta-carotene can be both an antioxidant and a pro-oxidant in the human body and that beta-carotene can exacerbate the carcinogenic effects of ultraviolet rays.

The U.S. Preventive Services Task Force (USPSTF) recommends against using beta-carotene supplementation for the prevention of cardiovascular disease (CVD) or cancer.

It's important to emphasize caution when it comes to these natural products. It wasn't long ago that, after finding that people who ate a diet rich in foods containing beta-carotene had a lower risk of lung cancer, researchers set out to study the potential effect of supplements of beta-carotene on risk. Unlike the reduced risk seen with dietary beta-carotene, however, beta-carotene in supplement form was associated with an increased risk of developing the disease.

The USPSTF found 6 randomized clinical trials (RCTs) reporting on health outcomes associated with beta carotene supplementation (JAMA 2022). Two trials conducted in persons who smoke or were exposed to asbestos in the workplace found a significantly increased risk of lung cancer with beta carotene supplementation (NEJM 1994) and beta carotene plus vitamin A supplementation (NEJM 1996).

A study published in 2023 by Newcastle University in the UK found that eating more carrots is related to a reduced incidence of cancer, but taking beta-carotene had no such effect.

Vitamin E

Vitamin E is an antioxidant, effective in eliminating free radicals, promoting anti-aging, and improving immunity. However, a randomized controlled trial found that vitamin E supplementation significantly increased the risk of prostate cancer in healthy men. More than 30,000 participants from the United States, Canada, and Puerto Rico took a daily dose of 400 IU of vitamin E for seven to 12 years, revealing a 17 percent higher risk of prostate cancer than the placebo group.

A study published in Cell in 2019 found that long-term supplementation of vitamin E and the antioxidant N-acetylcysteine may further promote lung cancer metastasis.

The USPSTF does not recommend using vitamin E supplements to prevent CVD or cancer, citing a comprehensive analysis of nine randomized trials that demonstrated no benefits.

Although vitamin E is a good antioxidant, too much of it can cause gastrointestinal bleeding and other conditions, Dr. Tzung-Hai Yen, a professor in the Department of Nephrology and director of the Clinical Poison Center at Chang Gung Memorial Hospital in Taiwan, told The Epoch Times.

This is especially the case for people with chronic diseases, Yen said. They need to be more cautious because many health products might not suit them. They should first seek advice from a physician before taking vitamin E supplements.

Vitamin B in High Doses

A large U.S. study found that men who took high-dose vitamin B6 (at least 20 mg/day) or B12 (at least 55μg/day) supplements had almost double the risk of lung cancer compared with those who did not take them.

A large study in the United States identified a correlation between high-dose vitamin B6 (at least 20 mg/day) and B12 (at least 55 μg/day) supplementation in men, nearly doubling their risk of lung cancer compared with non-users.

Published in the Journal of Clinical Oncology, this study involved 77,118 Americans aged 50 to 76 and found that men supplementing with either vitamin had a 30 to 40 percent increased risk, particularly among smokers.

However, there was no association between vitamin B6, B9 (folic acid), and B12 supplementation and lung cancer risk in women. Data showed that the participants’ intake of both B6 and B12 far exceeded the U.S. government’s recommended daily intake of 1.3 mg/day and 2.4 mcg/day.

Supporting evidence from a case-control study with 5,183 case-control pairs published in the International Journal of Cancer linked higher vitamin B12 levels with an increased overall lung cancer risk. The study also analyzed genetic data from 29,266 lung cancer cases and 56,450 controls and reached the same conclusion.

Nicotinamide riboside supplements and Cancer

Research from an international group of scientists and chemists also found that high levels of NR (nicotinamide riboside) could lead to an increased risk of developing cancer. A 2022 study by researchers at the University of Missouri found that taking nicotinamide riboside supplement may contribute to risks of brain cancer. The vitamin, called nicotinamide riboside, or NR for short, is a variant of B3. Taking the nutritional pill may lead to increased chances of breast cancer and brain metastasis, according to the study‘s results. Metastasis is when cancer cells spread through the body, causing multiple tumorous growths beyond an initial location.

“Some people take them [vitamins and supplements] because they automatically assume that vitamins and supplements only have positive health benefits, but very little is known about how they actually work,” Elena Goun, an associate professor of chemistry at University of Missouri said. “Because of this lack of knowledge, we were inspired to study the basic questions surrounding how vitamins and supplements work in the body.”

Conclusion

When interpreting scientific studies, let’s remember that cell culture results are trumped by mouse results. Mouse results are trumped by human results. Case studies & small human trial results are trumped by double-blind placebo controlled ones.

The best way to prevent cancer is by maintaining overall good health through a nutritious, whole-food diet rich in fruits and vegetables, along with a healthy lifestyle. No supplement can compensate for an unhealthy lifestyle, which includes physical inactivity, heavy smoking, excessive alcohol consumption, chronic stress, and obesity.

Supplement strategies should be part of a comprehensive broad multi-modal approach to cancer prevention and treatment that may also include other interventions. Each individual’s needs and responses to different approaches will vary, making it essential to consider a combination of options and several strategies for optimal outcomes. That said, there is no single miracle approach alone that can prevent and treat all cancers for everyone.

While there’s no silver bullet supplement, there are some anti-cancer supplements on the market that may help you keep the disease at bay or stop it from getting worse. Whether you’re living with cancer, a survivor, or just concerned for your health, talk to your doctor to determine the best treatment for you. 

For more information on treatment, causes and prevention, screening, and the latest research, check out this comprehensive resource page (by cancer type): https://cancer.aestheticsadvisor.com/p/cancer-types-by-system.html.

Note: This is an abridged version of a more comprehensive guide on diet and lifestyle for cancer prevention that reviews how diet, supplements and lifestyle can greatly reduce the risk of cancer. Check out the full guide here: I-PREVENT CANCER protocol: An Evidence-Based Guide to Cancer Prevention (2025 Edition)

Key Takeaways

The best way to prevent cancer is to combine a personalised menu of strategies by maintaining good overall health, like from eating a nutritious whole-food diet with lots of fruits and vegetables, avoid ultra processed foods, avoid sugar and maintaining a healthy lifestyle. 

Everyone’s situation is different, however, it is important to arm yourself with healthcare and medical knowledge that cancer doctors (Oncologists) may simply not give you.

Whether you’re living with cancer, a survivor, or just concerned for your health, talk to your doctor to determine the best treatment for you. 

• Diet and Supplement strategies should be part of a comprehensive broad multi-modal approach to cancer prevention or treatment that may also include other proven interventions. Each individual’s needs and responses to different approaches will vary, making it essential to consider a combination of options and several strategies for optimal outcomes. That said, there is no single miracle approach alone that can prevent all cancers for everyone.
• You could also complement your research and read more from the American Cancer Society site. The site has comprehensive information on cancer. You could read more on cancer prevention by cancer type here: http://www.cancer.gov/cancertopics/prevention
• For more information on treatment, causes and prevention, screening and research, check out this comprehensive resource page (by cancer type): https://cancer.aestheticsadvisor.com/p/cancer-types-by-system.html.
• For information on diet and lifestyle for cancer survivors, check out: I-TREAT Cancer Protocol: Diet and Lifestyle Guide For Cancer Survivors.

Disclaimers

• Although this is a comprehensive guide, please do not consider this guide as personal medical advice, but as a recommendation for use with professional providers. Consult with your doctor and discuss with her/him.
• Our aim here isn't to replace your doctors' advice. It is intended as a sharing of knowledge and information. Do take note that most strategies are not 100% protective against cancer. It's a continuous struggle between the immune system and the cancer cells. 

RELATED:

Top Alternative Cancer Treatments that Work: Evidence Based (2025 Edition)

The Cancer Risk Reduction Protocol to reduce Risk by 95%? (Dr Justus Hope)

Cancer 101: Causes, Types, Diagnosis, and Modern Treatments 

Fenbendazole vs Mebendazole for Cancer

Fenbendazole vs Ivermectin for cancer

Joe Tippens Protocol Fenbendazole

Fenbendazole: Questions Answered, Things to Know, Useful Tips

Mel Gibson had 3 Friends cure their Stage Four Cancer with Fenbendazole and Ivermectin

Nicotinamide riboside supplements and cancer

Read More: This article is part of the Winning the War on Cancer series.