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Cancer prevention–supplements

Last updated on August 24th, 2019 at 11:46 am

Potential causes for cancer are numerous. Infections. Radon gas. Cigarette smoking. Sun exposure. Obesity. With over 200 types of cancer, each with a different pathophysiology, there may be an equal (and probably greater) number of causes. Although many causes can be easily eliminated, such as stopping smoking, testing your house for radon, getting an HPV vaccine to prevent human papillomavirus infections, and wearing sunblock to reduce the risk of melanomas, the sheer complexity and number of types of cancer means that there is probably not going to be any simple panacea to preventing (or even curing) cancer. In fact, some hereditary cancers, such as those individuals who carry genes that are implicated in breast and ovarian cancers, may not be preventable at all.

Other than eliminating direct risks, are there things that can be done to actually prevent “cancer”? Once again, with over 200 types of cancer, this may be an impossibility, but the two most popular cancer prevention ideas are supplements and nutrition (which will be discussed at a later date). Vitamins and other supplements are a $61 billion industry in the US. They generate these sales with minimal regulation, minimal quality control over the quality and dosage, and no requirement to actually provide evidence that it does anything. The FDA only gets involved with the industry if there’s some dangerous side effect, or when the claims of the industry are so outrageous that the FDA has no choice but to get involved.

But do supplements actually do anything, especially with cancer? A recent article in the Journal of the National Cancer Institute, a highly respected peer-reviewed journal, “Dietary Supplements and Cancer Prevention: Balancing Potential Benefits Against Proven Harms” by María Elena Martínez and others, observed that:

…human experimental studies have uncovered the following: β-carotene does not prevent non-melanoma skin cancer recurrence; β-carotene and α-tocopherol with vitamin C do not protect against adenoma recurrence; β-carotene and vitamin A do not protect against lung cancer incidence (17); α-tocopherol and β-carotene do not prevent lung cancer; β-carotene does not prevent lung cancer; vitamins C and E do not protect against total cancer incidence; and α-tocopherol, vitamin C, and β-carotene do not protect against total cancer or cancer mortality. Based on a review of trial data, a Cochrane report concluded that there was no convincing evidence that β-carotene, vitamin A, vitamin C, or vitamin E supplements, given singly or in combination, prevent gastrointestinal cancers.

The article also discussed the “Selenium and Vitamin E Cancer Prevention Trial” (SELECT) that showed completely negative results with regards to cancer prevention. For example, there was no evidence that supplements decreased the risk of prostate cancer; in fact, the results showed that there was an increased risk. To quote Martinez et al, “organic selenium appears to provide no cancer prevention benefit.” 

The concerns about using supplements is far more serious than just not doing anything for cancer prevention, but they might also increase the risk of cancer. Martinez et al. also discussed where these supplements actually increased of cancer harm:

Several antioxidant trials have actually reported increased risks with supplementation. The most prominent example, β-carotene and lung cancer, was tested in two RCTs in high-risk populations of heavy smokers and asbestos-exposed individuals. Individuals randomly assigned to β-carotene in the Beta-Carotene and Retinol Efficacy Trial (CARET) trial had a 39% increase in lung cancer incidence compared with those in the placebo arm; the ATBC trial found a 16% increase in risk of lung cancer associated with β-carotene. With prolonged follow-up, NPC investigators found that selenium supplementation statistically significantly increased the risk of squamous cell skin cancer by 25% and total non-melanoma skin cancer by 17%. The increased risk was particularly marked among individuals in the highest tertile of circulating selenium levels just before the start of the trial. The most recent illustration of the possibility that pharmacological doses of antioxidants may not have the intended effect comes from the extended follow-up in the SELECT trial, which reported that α-tocopherol increased risk of prostate cancer by a statistically significant 17%; these results led the authors to conclude that consumers should be skeptical of health claims related to unregulated over-the-counter products.

So, taking beta-carotene, alpha-tocopherol or retinol increase lung cancer, squamous cell skin cancer, non-melanoma skin cancers, and prostate cancer risks by significant levels. In fact, not only are these expensive supplements not useful in protecting yourself from cancer, they increase your risk. If some drug from Big Pharma were found to do have this risk (despite actually having a positive benefit), the pseudoscientific alternative medicine industry (aka Big Herbal), would be using it as their strawman argument du jour to prove that their unproven (and potentially dangerous) products are somehow better.

Martinez et al. then examined what effect folate supplements may have on cancers. Supplementation with folate to decrease the risk of certain types of birth defects, especially neural tube defects, is supported by the strongest possible evidence. But other than that critical use (which should never be stopped, unless some other evidence appears), what can folic acid do? There are frequent claims by Big Herbal that folate prevents cancer, but the best research disputes such claims. The authors first state that the evidence that folate can prevent cancer just isn’t there. In fact, there is actually evidence that it can contribute to some cancers; for example, there is evidence that long-term folic acid supplementation increases the risk of advanced colorectal adenomas, prostate cancer, and breast cancer. Unfortunately, the US and other countries have mandated folic acid fortification of foods, which has the very narrow benefit of preventing birth defects, and that can be handled with appropriate pre-natal supplements. Once the mother has delivered the baby, the need for folic acid drops off to the amounts normally obtained in a balanced diet.

The Big Herbal crowd claims that vitamin D is the wonder supplement that prevents all cancers. They even claim it cures some cancers. Martinez et al. also examined the effects of vitamin D and calcium, and made the following conclusion: 

There have been many epidemiological investigations of blood 25 hydroxy (OH) vitamin D [25(OH)D] concentrations and cancer-related endpoints, and meta-analyses of these have shown statistically significant inverse associations between serum 25(OH)D and colorectal adenoma and colorectal cancer, whereas the results for prostate cancer have largely been null. For breast cancer, the relationship with serum 25(OH)D levels varies by study design; case-control studies generally demonstrate inverse associations, and prospective studies have been null; because blood levels are collected after the onset of cancer in case-control studies, the potential for bias in these studies must be considered. Clearly, clinical trials are needed to elucidate any preventive effect of vitamin D. To date, three short-term RCTs of vitamin D and cancer endpoints have been completed; one showed no direct effect of vitamin D supplementation on cancer mortality, the second showed no reduction in breast or colorectal cancer incidence by a vitamin D/calcium combination, and the third showed a reduction in total cancer incidence by a calcium/vitamin D combination vs placebo. As concluded in a recent meta-analysis, because of the potential confounding inherent in observational studies and the limited data from clinical trials, evidence is currently insufficient to draw conclusions about the efficacy of vitamin D supplementation for cancer prevention.

The only possible method to determine a causal effect would be to measure blood vitamin D in a large population before and after certain types of cancer. Unfortunately, there is also conflicting evidence that high levels of vitamin D consumption suggests a correlation between increased risks of pancreatic and prostate cancer. Calcium supplementation showed a similar lack of positive results. Big Herbal tends to focus only on the positive results, by “quote-mining” research that supports their beliefs, rather than weighing all of the evidence to see if it supports the hypothesis. That’s why review articles published in well-respected peer-reviewed journals are the diamond-studded platinum standard of evidence.

Finally, Martinez et al. concluded:

Nutritional supplementation is now a multibillion-dollar industry, and about half of all US adults take supplements. Supplement use is fueled in part by the belief that nutritional supplements can ward off chronic disease, including cancer, although several expert committees and organizations have concluded that there is little to no scientific evidence that supplements reduce cancer risk. To the contrary, there is now evidence that high doses of some supplements increase cancer risk. Despite this evidence, marketing claims by the supplement industry continue to imply anticancer benefits. Insufficient government regulation of the marketing of dietary supplement products may continue to result in unsound advice to consumers. Both the scientific community and government regulators need to provide clear guidance to the public about the use of dietary supplements to lower cancer risk.

There is an old joke that people who take lots of supplements have the most expensive urine in the world, since much of the excess supplements are just filtered out by the kidneys. There is just so little evidence that supplements work, and so much evidence that many of them increase your risk of diseases such as cancer, there is no reason to waste so much money on useless and potentially dangerous supplements. Of course, most individuals will just ignore this because their “belief” matters more than “evidence.” Evidence, especially that from careful, well-designed research always trumps anecdote and belief. And basing a decision on research-mined studies without weighing all of the evidence is a mistake that could lead to more harm than benefit.

Michael Simpson

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