22.08.2013 Natural Health

Supplements and Cancer Prevention

Peter Dingle PhD examines the important role of supplements in preventing some cancers

There is no miracle cure for cancer and there never will be. The rates of cancer and death from cancer continue to increase, despite the billions of dollars spent treating the illness. Only a few minor cancers are treated effectively with modern techniques yet we still keep trying. Three cancers, however, are starting to show significant reductions in their occurrence: lung cancer, the largest killer because of education and prevention during the past 30 years; some oestrogen-dependent breast cancers as a result of the removal of hormone replacement therapy; and stomach cancers because of the treatment of the bacteria Helicobacter pylori with simple antibiotics.

Most of the cancers of today were either rare or unheard of just 100 years ago and are still rare in many countries where people live on traditional diets. Breast cancer rates, for example, are around 1% of the women in populations living on traditional foods in rural Japan and China but around 13% in Australia. When people move to Australia or the US, they take on the same disease rates as the country they move to within a generation. It is not genetic.

Folic Acid

There is a large body of epidemiological studies that shows a strong association between micronutrient deficiencies and the development of cancer. In 1998, Harvard University released a report on its highly influential Nurses' Health Study. The longitudinal study, which involved more than 90,000 nurses and was conducted over a period of 20 years, is one of the most comprehensive studies ever undertaken on the causes of colon cancer. ]

The study showed that supplementation with folic acid was one of the most influential factors in reducing the incidence of colon cancer.(1) It further showed that women who used multivitamin supplements containing folic acid for at least 15 years were 75% less likely to develop colon cancer than women who never took multivitamins.

One significant finding was that folic acid obtained from supplements was shown to have a stronger protective effect against colon cancer than folic acid consumed in the diet. The 1999 Harvard Report on Cancer Prevention reemphasises this point, stating that the use of a multivitamin supplement containing folic acid is one of the most significant factors in reducing colon cancer, just behind physical activity and reduced consumption of red meat. The report states that the higher protective effect of folic acid exposure from supplements than from food may be due to the higher dose and bioavailability of the folic acid found in multivitamins.(2) This significant finding is backed up by the results of a 1996 study from the University of Ulster in Northern Ireland, which showed folic acid obtained from nutritional supplements was better at reducing the incidence of neural tube birth defects than the folic acid obtained from food.(3)

In a study of 14,916 men, increased blood levels of pyridoxal-5'-phosphate (PLP), the active form of vitamin B6, were significantly associated with a reduced risk of colorectal cancer. PLP levels were inversely linked with risk of colorectal cancer, with increasing levels found to decrease the risk by around 50%.(4) The study's authors also reported that PLP levels were inversely correlated with blood levels of homocysteine, the inflammatory markers C-reactive protein (CRP), tumour necrosis factor-alpha receptor 2 and interleukin-6 (IL-6). This may also explain some of the mechanism behind the benefits of vitamin B6. An earlier study found that increased intake of vitamin B6 from dietary and supplement sources can reduce the risk of colorectal cancer by more than 20%.(5)

On the other side of the equation, low intake of vitamin B6 may increase a man's risk of colorectal cancer by 31%.(6) A study of mice found moderate deficiency of folate, riboflavin and vitamins B6 and B12 together may promote the risk of DNA damage and increase the risk of colorectal cancers.(7) The study found that mild depletion of all four B vitamins was needed to promote the risk of tumour formation through Wnt signalling, a cellular signalling pathway linked to more than 85% of colon cancers.

Researchers reported that while conditions of mild folate deficiency alone may not be sufficient to observe an effect on Wnt signalling, the concomitant deficiency of folate and other B vitamins may produce abnormalities of the type associated with human colorectal cancers.

Folate, Vitamin B6 and Vitamin B12

Folate, vitamin B6 and vitamin B12 are also thought to play an important role in cancer prevention. This is because the vitamins play an important role in maintaining the integrity of DNA and regulating gene expression, both critical processes in healthy cell function. In a study of 5,442 women with an average age of 62.8 over the course of 7.3 years, half of the women received a daily supplement of folic acid (2.5 milligrams), vitamin B6 (50 milligrams) and vitamin B12 (1 milligram), while the other half of the women received a placebo.(8) In women over the age of 65, the supplementation was associated with significant 25% and 38% reductions in the risk of invasive and breast cancer, respectively.

Role of Methylation

Another study identified the role of methylation, which affects gene signalling, as a possible aspect of the benefit. Current multivitamin users had a 43% lower risk of gene methylation.(9) A study of blood levels of 899 people with lung cancer matched with 1,770 cancer-free people found higher blood levels of vitamin B6 were associated with a more than 50% reduced risk of lung cancer.(10) The study also found that high folate levels combined with methionine and B6 were associated with a 66% reduction in lung cancer risk. This amazing finding has not been widely reported in the media, but it confirms a growing body of evidence gathered over the last 40 years that B vitamins are important for preventing diseases such as cancer.

One study researching the use of multivitamins in breast cancer survival found no difference between those who never took multivitamins or who just began to take them once they were diagnosed.(11) However, those women taking multivitamins before they were diagnosed were 24% less likely to have a recurrence than women who had not been taking supplements before their breast cancer was found. In another study, the same researchers found that women who took vitamins C and E had fewer recurrences of breast cancer (by 27% and 29%) than those who did not.(12) They also found that the breast cancer patients who took vitamin E were 24% less likely to die from any health-related issue than their counterparts who did not take that nutrient.

Selenium Levels

Increasingly, studies have demonstrated the incidence of chronic disease correlating directly with selenium intake levels. Most significantly, in the 1970s it was identified that national cancer rates directly correlated with levels of selenium in the soil. Low levels of the mineral selenium correlated to high levels of cancer.(13) Selenium is known as "the anti-cancer mineral" and is an essential trace element involved in several key metabolic activities via enzymes that are essential to protect against free radical (oxidative) damage and to regulate the immune system. Selenium is an essential part of glutathione peroxidase, an enzyme found to remove one of the major free radicals, hydrogen peroxide.

A number of very large studies on selenium supplementation, such as those in China and Finland, have found significant reductions in cancer rates. In support of this, a study found that supplementation with 200 micrograms of selenium for six weeks increases the activities of blood enzymes such as glutathione and reduces the levels of PSA, prostate-specific antigen, a marker for prostate cancer. It was only a small study of 30 middle-aged US men but the authors of the study wrote, "If selenium could lower PSA [prostate-specific antigen] in healthy, middle-aged men, then it could be proposed that selenium can lower prostate cancer risk in some men, especially as part of an overall dietary plan."(14)

Hundreds of studies have shown the benefits of selenium in preventing cancers. In a nine year, double-blind randomised clinical trial, researchers showed that a daily 200 mcg dose of supplemental selenium significantly reduced incidence and mortality levels of cancer. The study showed significant preventive effects for cancers of the lung, prostate, colon and rectum, but no reduction in the risk of breast or bladder cancer. A 200 mcg dose of selenium per day produced a 50% reduction cancer mortality compared to a placebo group not receiving supplementation. The study also showed a 37% reduction in the incidence of all types of cancer combined (including breast and bladder cancer) and a highly significant 63% reduction in the incidence of prostate cancer.(15,16) In another study, after eight years of follow-up, high selenium blood levels were associated with a 42% risk reduction compared to individuals with low selenium levels.(17) Similar reductions in prostate cancer risk were observed in multivitamin users, with the highest compared to the lowest quarter of selenium blood levels demonstrating a risk reduction of 39%. Higher serum selenium levels were associated with a 35% reduced risk of prostate cancer amongst smokers.

In support of this, in the US, the FDA, an ultra conservative industry-led organisation, has allowed two claims for selenium:

It produces anti-cancer substances in humans;and
It decreases the risk of certain forms of cancer.

Other studies have shown that high levels of selenium in the body have been linked with lower levels of lung, prostate and colorectal cancers. Selenium is thought to reduce the risk of developing cancers in two ways. First, as selenium is an antioxidant, it helps protect the body from dangerous free radicals. Second, selenium has been known to prevent or slow tumour growth. It does this in such a way that selenium enhances immune cell activity and suppresses the development of the blood vessels leading to the tumour, resulting in reduced or no cancer growth. Studies have also shown that people with low levels of selenium have a greater incidence of heart disease.

A study from the University of Queensland - Queensland having one of the highest rates of skin cancer in the world - found that the highest average selenium levels of between 1.3 and 2.8 micromoles per litre were associated with a 57% reduction in the incidence of basal cell carcinoma and a 64% reduction in the incidence of squamous cell carcinoma, compared to the lowest average selenium levels of between 0.4 and 1.0 micromoles per litre.(18) That is, the highest levels of blood selenium were associated with a reduction in both main forms of skin cancer.

In an amazing study of supplementation to prevent cancer, sodium selenite (SS), magnesium chloride (magnesium), ascorbic acid (vitamin C) and retinyl acetate (vitamin A) were given on their own or in combinations to adult female rats with mammary cancer induced by 30 milligrams of 7,12-dimethylbenz[a]anthracene (DMBA). In the rats given the cancer-causing chemical DMBA alone, 100% of the rats developed mammary tumours. When the supplements were given singly, the tumour incidences were reduced to 51.77% (sodium selenite), 46.4% (magnesium), 57.1% (ascorbic acid) and 48.1% (vitamin A). When the supplements were given in combinations of twos, the tumour incidences were further reduced to 29.5% (selenium + magnesium), 31% (selenium + ascorbic acid), 29.6% (selenium + vitamin A), 25.9% (magnesium + ascorbic acid), 31.8% (magnesium + vitamin A) and 34.6% (ascorbic acid + vitamin A). Administration of supplements in combinations of threes resulted in still further reduction of tumour incidences to 22.2% (selenium + magnesium + ascorbic acid), 19.2% (selenium + magnesium + vitamin A), 16% (magnesium + ascorbic acid + vitamin A) and 23.1% (ascorbic acid + vitamin A + selenium). When all four supplements were given concurrently the tumour incidence was only 12%. Further, the number of tumours per tumour-bearing animal declined with the increase in the number of agents used in combination for supplementation.

The question I have to ask is why don't we supplement when it is so cheap and effective and has the potential to save so much pain and suffering?

DISCLAIMER: Dr Peter Dingle is a researcher, educator and public health advocate. He has a PhD in the field of environmental toxicology and is not a medical doctor.


Giovannucci et al. 1998Harvard Report on Cancer Prevention 1999Wald 1996Lee et al. 2009Cancer Epidemiol Biomarkers Prev. Vol. 17, pp. 171-182Ishihara et al. 2007Liu et al. 2007Zhang et al. 2008Stidley et al. 2010Johansson et al. 2010Greenlee and Kwan 2011aGreenlee and Kwan 2011bShamberger 1970Zhang et al. 2011Clark et al. 1996Colditz 1996Peters et al. 2007van der Pols et al. 2009
Peter Dingle

Dr Peter Dingle (PhD) has spent the past 30 years as a researcher, educator, author and advocate for a common sense approach to health and wellbeing. He has a PhD in the field of environmental toxicology and is not a medical doctor. He is Australia’s leading motivational health speaker and has 14 books in publication.