More evidence Vitamin D supplementation does not reduce breast cancer risk

vitamin-DPotential causes for cancer are numerous. InfectionsRadon gasCigarette smokingSun 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 some cancers can be easily prevented, such as never smoking, which reduces your risk of lung cancer, one of the most prevalent cancers in the USA, by over 85%. Or getting the HPV vaccine (Gardasil or Silgard) which blocks HPV infections that are associated with several types of cancer, including cervical, anal, and penile cancers. Unfortunately, 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 three most popular cancer prevention ideas are diet, vitamins and other types of nutritional supplements. 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 the supplements do what is claimed by the supplement industry, aka Big Herbal. 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.

Not too astonishingly, there just hasn’t been much evidence that cancer can prevented with supplements. Prostate cancer and fish oil? May actually increase risk, but generally no effect. Prostate cancer and soy? Nothing there either. Folic acid and cancer? May actually increase risk. 

The number of supplements that have failed, in clinical trials or epidemiological studies, to show any evidence of efficacy in preventing cancer is fairly large. Vitamin E and seleniumBeta-carotene, alpha-tocopherol or retinol actually increase lung cancer, squamous cell skin cancer, non-melanoma skin cancers, and prostate cancer risks by significant levels.

Recently, scientists have focused on vitamin D supplementation and breast cancer prevention. Researchers, in a meta-review of two studies involving thousands of women, have found evidence that vitamin D supplements do not help prevent breast cancer. The authors conclude that “based on our results and limited trial evidence, vit D supplementation seems not to be associated with a reduced risk of breast cancer development in postmenopausal women.” The participants in the studies were randomly assigned to take Vitamin D or a placebo. The larger study enrolled 5,292 women, and the smaller one included 1,180 women. In the larger study, individuals were given either 800 IU of vitamin D3, 1000 milligrams of calcium, both supplements or a placebo for 24 to 62 months. For the second study, participants were given either placebos or 1,400 to 1,500 milligrams of calcium and 1,000 IU of vitamin D3.

Even though the size of the two studies were large, and the results were statistically significant there are a couple of issues: first, the length of the studies were around 5 years, which may not be long enough for significant results. However, if vitamin D were to have an effect, there would be evidence that showed a small response early, as one would expect a curve that showed early results. Also, some individuals in the alternative medicine world have complained that there wasn’t sufficient levels of Vitamin D given to the participants. But once again, if there were some sort of dose-response, we would have seen some effect, especially given the power of the study with so many participants. The thing is that this isn’t the first report that vitamin D has no effect on breast cancer.

Recently, three large studies have been published that show that vitamin D probably has no effect on breast cancer risks. These are the type of studies that I consider the best of the best, ones that have large cohorts which give better statistical significance. As I’ve discussed before, the quality of scientific sources matters. In the science denialism world,  alternative medicine, cherry-picks research that supports their beliefs, rather than looking at the highest quality research and determine if it supports the hypothesis (in this case, whether vitamin D has any benefit to preventing breast cancer).

  • In a study of 36,282 postmenopausal women 50–79 years of age, who were randomized into two groups, a placebo or 600 IU daily of vitamin D, the authors concluded that “while evidence for a reduction in breast cancer risk and total invasive cancer risk among calcium plus vitamin D users was only suggestive.” Statistically, the evidence was weak, despite the relatively large number of subjects in the study, and cannot be accepted as “conclusive.” However, the authors suggest that the study wasn’t set up to examine cancer risks (there were many confounding variables). But the study does conclusively support that “long-term use of calcium and vitamin D appears to confer a reduction that may be substantial in the risk of hip fracture among postmenopausal women.” 
  • In a large study of nearly 400,000 women in Europe, the authors determined that there was no significant effect on cancer risk with calcium and vitamin D intake. They conclude that “in this large prospective cohort, we found no evidence for an association between dietary vitamin D or calcium intake and breast cancer risk.” This is a huge study, which should be able to identify small changes, and none were found.
  • Finally, researchers examined the levels of vitamin D in the blood of patients with breast cancer, and determined that “this large prospective study does not support a relationship between circulating 25(OH)D and risk of breast cancer, except possibly in younger women. These results add to a growing body of evidence from prospective studies and randomized trials that suggests higher vitamin D levels do not reduce breast cancer risk.”

What can we conclude? There is strong evidence that vitamin D does not lower the risk of breast cancer, even though there is some suggestive evidence (and in science that means it isn’t statistically valid and would require significant research to make it more than just suggestive). However, because vitamin D supplementation has other critical benefits for women, for example, substantial reduction in hip fractures, a possible reduction in breast cancer is a potential benefit.

However, there isn’t a dose-response of vitamin D consumption and these benefits. Given that there is no conclusive scientific evidence that vitamin D reduces breast cancer, it would be ridiculous to assume that more vitamin D will suddenly make the risk of breast cancer go away. Furthermore, too much vitamin D can be dangerous

Obviously, cancer is a scary disease, mainly because we can’t control it. We don’t want to hear that it may be genetic. Or random. Or completely unpreventable. But don’t fall for the scam of buying supplements in the hope that your risk will be reduced. It probably will have no effect on your risk.

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The Original Skeptical Raptor
Chief Executive Officer at SkepticalRaptor
Lifetime lover of science, especially biomedical research. Spent years in academics, business development, research, and traveling the world shilling for Big Pharma. I love sports, mostly college basketball and football, hockey, and baseball. I enjoy great food and intelligent conversation. And a delicious morning coffee!