One of my favorite topics to debunk is the use of supplements to prevent (or worse yet, cure) cancer. As I have discussed in the past, supplements are, with just a couple of exceptions, worthless in preventing cancer.
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 for “cancer.” Although many causes of cancer can be easily avoided, 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.
But because cancer is so frightening, and treating it is risky, debilitating and, in some cases, fruitless, we look for the easy solution, the easy prevention with a pill. But the evidence science has found indicates that this doesn’t really work. Of course, according to 2012 cancer statistics, 577,000 people died of various cancers in 2012, and about 160,000 died directly as a result of smoking (or second hand smoking). So, you can easily drop your risk dying of cancer by more than 25% just by quitting smoking. Otherwise, it’s just not that simple.
One of the current “fads” in preventing breast cancer is taking vitamin D supplements. Woo-Master Joe Mercola touts vitamin D for breast cancer prevention (and you can buy it from him too), so you know it’s a part of the alternative medicine belief (not evidence-based) system. Most of his claims are based on cell culture and animal models, and there hasn’t been a lot of good clinical or epidemiological studies to support his beliefs.
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.
So what’s the conclusion? If you’re a woman (of probably any age), getting more vitamin D (through a few minutes in the sun, drinking milk or supplements) has important long-term benefits. Reducing the risk of breast cancer is probably not one of those benefits.
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