Numerous studies have addressed the possible effects of such supplements and now Dr. David Jenkins and his team at the University of Toronto have done a spectacular job in scouring the literature for all relevant studies carried out during the last four years. Individual studies don’t mean very much in science, but pooling them offers meaningful results. That is exactly what Jenkins and colleagues did. This is an important effort because some 50% of the population takes some sort of supplement so that a risk-benefit analysis is certainly welcome.
People taking supplements comprised of some combination of vitamins A, C, E and beta-carotene will be disappointed to learn that these had no effect on preventing any form of CVD. That is somewhat surprising because these are “antioxidants” that in theory should have an effect since they neutralize free radicals that have been implicated in damage to blood vessels. Not only were these antioxidants ineffective, they were associated with a slight increase in all-cause mortality during the period of study. This is not likely to be a cause and effect relationship, rather it is likely that people who have health issues are more likely to take supplements.
The only positive effect that emerged from all the collected data was a slightly reduced incidence of stroke associated with folic acid as an individual supplement, as well as with taking B vitamins that include folic acid. But, there is a “but” here. Most of the studies that show a benefit were carried out in China, where unlike North America, folic acid is not added to flour. It is therefore possible that correction of a deficiency, one that does not exist here, is responsible for the positive effect on CVD that was found.
The statistics on the folic acid and B vitamin supplements are significant, meaning that the results are unlikely be due to chance. That, however, does not mean that they are of great practical significance. To answer that question, we have to ask how many people would have to take a folic acid supplement to prevent a single stroke. That number, the so-called number needed to treat (NNT), turns out to be 167! For an individual those are not great odds, but for a population at large, a significant number of strokes can be prevented. To complicate things further, niacin, also a B vitamin, was associated with an increase in mortality, albeit only when used in combination with statins. As far as the possible harm from antioxidants goes, the number needed to harm (NNH) is 250. If this many people take antioxidant supplements, only one is expected to experience harm. Not a great risk, but given that no benefits were seen with antioxidants, there seems to be no point in taking them.
Now for another “but.” Fruits and vegetables contain many other antioxidants than vitamins, such as a host of polyphenols that in some studies have shown a reduced risk for cardiovascular disease. Supplements of these were not looked at in this study. Nor was there consideration of other indications for taking vitamin or mineral supplements, such as prevention of osteoporosis, depression or effects on the immune system.
What then are we to make of this analysis of a large number of studies that have examined the relationship between vitamin and mineral supplements and cardiovascular disease? There is no compelling data to justify the use of these products, save for a possible slight benefit from folic acid alone or in combination with other B vitamins. Even that benefit comes with an asterisk since the benefit has mostly been observed where flour is not fortified with folic acid. A second smaller asterisk can also be added. Some studies, although not any of the ones in this compilation, have linked increased intake of folic acid with prostate cancer.
Take away message: Get your vitamins and minerals from fruits and vegetables and not from a pill. But if you are on a diet that does not include folic acid fortified flour at all, then consider a supplement of B vitamins. I wouldn’t worry about the increased mortality risk from antioxidants, that is likely an artifact, but understand that they will have no effect on cardiovascular disease. If you want a real benefit, exercise! The evidence for benefit is overwhelming.
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