Over-use of some supplements can increase risk for cancer

Data presented at the annual meeting of the American Association for Cancer Research here in Philadelphia have again confirmed that the use of selenium and vitamin E supplements to raise levels of these agents to higher than normal levels is not a very good idea when it comes to cancer prevention.

This information first became evident in the results of the SELECT trial back in 2011. The new information presented by Byers and colleagues this week are based on a meta-analysis of data from about 20 studies, including two large clinical trials. These data confirm, in particular, that the use of vitamin E supplements may actually increase risk for prostate cancer if taken in excess of the recommended daily amount. See these reports on the CBS News and Medical Daily web sites for additional information.

Byers and his colleagues further report that high doses of β-carotene supplements can increase risk for lung cancer; selenium supplements are associated with risk for skin cancer; and over-use of folic acid (vitamin B9) can increase risk for colon cancer.

General guidance is that if one uses supplements in combination with diet to maintain levels of certain vitamins and minerals within the normal range, that’s okay, but its better to do it just with diet management. Excessive use of supplements to boost one’s levels of particular vitamins and minerals above the normal range can, however, be dangerous (as indicated by the examples above), and should only be done after careful consultation with one’s physician(s).

2 Responses

  1. I believe I’ve posted this before — June Chan’s (UCSF/Harvard) research suggests that you should test before supplementing with vitamin E and/or selenium. If you are low in either, it is wise to supplement; if you are normal or high, it is not.

  2. Cause, Association, Wrong Form?

    We need to bear in mind that association may be affecting many of these studies, rather than cause. For example, years ago selenium was thought to be helpful in warding off skin cancer, with some supportive data. Hence, it is very likely that some people worried about skin cancer started supplementing with selenium. It would not be surprising that an observational study would have findings influenced by people getting skin cancer who had taken selenium because they rightly figured they were at higher risk of getting skin cancer.

    Regarding vitamin E and prostate cancer, some of us have been concerned for well over a decade that the wrong form of vitamin E was used in the SELECT trial (as well as, as we later discovered, a dose that was excessively high, thereby causing a bleeding risk). The alpha-tocopherol form was used, instead of the gamma form that seemed a better candidate for reducing the impact of prostate cancer.

    I’m aware of the arguments and data. My decision is to keep my mind open.

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