Too Much Supplementation May Raise Cancer Risk

Taking more nutritional supplements than needed may increase a patient’s risk of cancer.

Tim Byers, MD, MPH, associate director for cancer prevention and control at the University of Colorado Cancer Center, recently discussed several studies suggesting a link between cancer and excessive use of dietary supplements at the American Association for Cancer Research Annual Meeting in April 2015.

“Since most nutritional supplements are untested for this [cancer risk] and will never be tested, I think 2 things are needed: caution to the public about potential health hazards from high-dose supplements and enablement of the FDA to become more engaged in matters of safety, efficacy, and advertisement,” Dr. Byers told Pharmacy Times in an exclusive interview.

In one 2014 study he referenced, researchers sought to determine whether vitamin B₁₂ and folic acid supplements could reduce osteoporotic fractures in elderly patients with hyperhomocysteinemia. They examined 2919 patients 65 years or older who either received vitamin B₁₂ and folic acid supplements or placebo for 2 years. The combined supplementation did not have an effect on osteoporotic fracture incidence, but there was some evidence that the supplements may help prevent fractures among those aged older than 80 years.

While the authors did not intend to study cancer outcomes, they did find more participants in the supplement group reported having cancer than the placebo group.

Another study Dr. Myers described was a 2013 Lancet article on the effect of folic acid supplementation on site-specific cancer incidence. While the researchers found the supplements did not increase or decrease the incidence of cancer in the first 5 years of treatment, Dr. Byers zeroed in on the 2-year mark.

At the 2-year stage of follow-up, 411 participants in the intervention group reported cancer, compared with 354 in the control group.

“The [relative risk] was 1.16 at 2 years, supporting potential short-term hazard,” Dr Byers told Pharmacy Times.

Dr. Byers has published his own findings on the topic in The Journal of the National Cancer Institute, where he and his fellow study authors gathered evidence pointing to high-dose supplements potentially increasing cancer risk.

For example, one trial found selenium supplements led to a 25% increase in the risk of squamous cell skin cancer and a 17% increase in the risk of total non-melanoma skin cancer.

While individuals with marginal or deficient nutrition may benefit from supplements, the researchers cautioned that, supplements could be more harmful than beneficial for those with adequate nutrition.

Dr. Byers said nutritional supplements should not be marketed for cancer prevention, and patients should not fall for the idea that “if a little of a nutrient is good, then a lot must be better.”

“If taken at the correct dosage, multivitamins can be good for you,” Dr. Byers said in a press release. “But there is no substitute for good, nutritional food.”