Do antioxidant vitamins impact prevalent causes of
Summary (Updated July 7, 2005)
There have been numerous large studies of the impact of
antioxidant vitamins (A/beta-carotene, C and E) on cardiovascular disease,
cancer and Alzheimer's disease. No significant decrease in the risk of these
diseases has been observed for people taking these supplements, relative to
people who do not take them. It is possible that they have a minor effect that
will be detected (that could be beneficial or detrimental) in future larger
studies. One meta-study does indeed claim to show that beta-carotene has a
negative effect on certain types of cancer incidence. Three studies providing additional results relating to vitamin E, published in 2005 (references 16-18) corroborate its lack of impact on most of the possible health effects studied. One study does seem to show a minor effect on cardiovascular deaths, but it remains to be seen whether this is a statistical fluke (or incomplete analysis), rather than a real effect.
with antioxidant vitamins could also be an issue. In a study presented in reference 15, they find that antioxidants lower HDL2 (a component
of HDL cholesterol that is thought to be the most protective). In that study, they find that Simvastatin
( a "statin" drug) combined with Niacin (a type of B vitamin) raise the HDL2 level by 60%. However when combined with
800 IU of vitamin E, 1000 mg of vitamin C, 25 mg natural beta carotene, and 100
microgram selenium daily, HDL2 was increased relative to a placebo only by 18%, a much poorer improvement.
So, if you are
eating plenty of fruit and vegetables, should you be taking supplements?
Certainly they are not going to significantly impact the major illnesses that antioxidants are
advertised to remedy. It is always possible that there are some rarer diseases
that could benefit from antioxidants, but they are have not yet been identified.
It is also possible that taking vitamins leads to a general improvement in daily
health, that is not illness-specific. However, a recent (2005) metasudy on vitamin C (reference 19) indicates that it has minimal (if any) impact of the severity and duration of the common cold. Likewise, maybe taking antioxidants for
20-30 years is beneficial - typical studies last for 5-10 years at the most.
However, I am not aware of any studies that support these possibilities. In
conclusion, there is no compelling evidence to support taking antioxidants; in
fact, it may even be detrimental in certain situations.
Please see update in epilogue.
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Modification - May 6, 2006