A recent article published in the Journal of the National Cancer Institute warns that health-minded consumers are taking too much Vitamin D.
Reports of consumers taking megadoses of Vitamin D may be attributable to a combination of supplement industry advertising practices that tout Vitamin D as a cancer preventive and TV health show advice that the majority of people unwittingly suffer from Vitamin D deficiency. In fact, in one episode of The Dr. Oz Show, a special guest urged viewers to take up to 10,000 IU of Vitamin D daily. To his credit, Dr. Oz states that he finds that dose surprisingly high and tells viewers that he sticks to his recommended 400-1000 IU of Vitamin D daily.
So what’s the harm in possibly taking too much Vitamin D or any other nutritional supplement? Is it not common knowledge that when our body has excess vitamins that our bodies eliminate the excess through our urine?
While it is true we do make what has been referred to as “expensive urine” through taking vitamin supplements that our body may not be in need of, part of the problem according to María Elena Martinez of the University of California-San Diego is that what is common knowledge is not always true.
"Undoubtedly, use is driven by a common belief that supplements can improve health and protect against disease, and that at worst, they are harmless," she and her co-authors write. "However, the assumption that any dietary supplement is safe under all circumstances and in all quantities is no longer empirically reasonable."
In a recent article titled "Dietary Supplements and Cancer Prevention: Balancing Potential Benefits Against Proven Harms," researchers hope to raise awareness about scientific evidence that too much of any vitamin can be harmful to a consumer and can increase rather than lower the risk of cancer.
Martinez and co-author Elizabeth Jacobs—a UA associate professor of epidemiology and a researcher at the Arizona Cancer Center—make the point that health-conscious people may be at the greatest risk of taking too many vitamin supplements because they are also more likely to eat healthier than the rest of the population and therefore not really need any extra supplements.
"A lot of literature has shown that often the people who take dietary supplements need them the least, so they already eat a good diet, they have a lot of nutrients in their diet, they exercise, they don't necessarily need extra nutrients," Jacobs said. "And those are the people who tend to take supplements—they are very health conscious, and that's where the danger is because you are already getting enough of these vitamins or minerals in your diet, and then you are adding more….if you are deficient in nutrients, taking a supplement is probably not going to cause any harm, but if you are already adequate in nutrients, then taking a supplement at a minimum has no benefit and in some cases has been shown to cause harm."
The authors of the paper base their vitamin overuse warning on observational studies of several supplements, including anti-oxidants, folic acid, vitamin D and calcium. What they found was that with respect to anti-oxidant supplements, “The importance of oxidative stress for carcinogenesis does not establish that the administration of supplemental antioxidants will protect against the carcinogenesis that oxidative stress may induce.”
Furthermore, they add that, “Supplementation by exogenous antioxidants may well be a two-edged sword; these compounds could, in vivo, serve as pro-oxidants or interfere with any of a number of protective processes such as apoptosis induction [normal cell death].”
From several antioxidant trials, they found reported increased cancer risks with supplementation and caution against taking dietary supplements for cancer prevention, saying that many experts have concluded that nutritional supplements have little or no benefit in cancer prevention and that additional randomized control trials—spanning many years instead of just a few—are needed to verify the effect of nutritional supplementation in cancer risk.
A past National Cancer Institute study reported no cancer protection from Vitamin D and the possibility of an increased risk of pancreatic cancer in people with the very highest Vitamin D levels. Megadoses of and above 10,000 IUs a day are also known to cause kidney damage.
"You aren't supposed to get the recommended dietary allowance (of nutrients) every day. It rarely happens. You are supposed to just average over time. You just do the best you can. But in the U.S., our problem isn't really under-nutrition, it's over-nutrition,” says Jacobs.
Image Source: Courtesy of MorgueFile
”Dietary Supplements and Cancer Prevention: Balancing Potential Benefits Against Proven Harms” Journal of the National Cancer Institute April 25, 2012; María Elena Martinez et al.