Inappropriate study designs may be the only reason why randomized controlled trials may not have found B vitamins and vitamin E to be effective in decreasing cardiovascular risk, suggests a new review.
The review took into account eight randomized controlled trials (RCTs) using B vitamins (folic acid, vitamins B6 and B12) and four trials using vitamin E that did not show any effects of vitamin supplementation in pre-venting diseases related to dysfunction of the blood vessels supplying the heart or the brain (1). Focusing on study design and contradictions in results, the review showed that the clinical trials had inappropriate designs and neglected the impact of some confounding factors, such as concomitant use of statins, acetylsalicylic acid and other drugs, which might have led to bias and a flawed interpretation of the data. The cardiovascular protective and preventive effects of statins and aspirin, for example, might have limited or removed the possibility of observing a difference in the number of disease occurrences between the vitamin and placebo groups.
The researchers concluded that the preventive effect of vitamins against cardiovascular disease cannot be disproven with regards to the negative trial evidence. Because of the inappropriate trial designs and flawed results of the large RCTs, no conclusions could be drawn from the trials, such as not recommending B vita-min supplements for the prevention of cardiovascular disease or associating vitamin E with an increased risk of hemorrhagic stroke. The latter may be explained by the combined action of vitamin E and aspirin, since antiplatelet and anticoagulant effects are cumulative when taken in combination. The scientists added that the B and E-vitamin supplementation could work in primary prevention, and that the large vitamin trials did not have enough participants to settle the debate on the effectiveness of vitamin supplementation in secon-dary prevention of cardiovascular diseases.
Whether or not B vitamins play a role in heart health by reducing levels of the amino acid homocysteine, reported to increase the risk of cardiovascular disease, is a disputed subject. While epidemiological studies have linked increased intake of B vitamins with reduced risk of cardiovascular disease, clinical trials including participants at risk of, or already suffering from, cardiovascular disease have produced null results. Studies investigating the antioxidant effects of vitamin E, which could potentially reduce the risk of atherosclerosis, have also been inconclusive.
Experts have already criticized that short-term B vitamin supplementation should not be expected to reverse the long-term development of heart disease or to compensate a lifetime of unhealthy living. Moreover, a set dose of a nutrient for a select period would be an inappropriate way to evaluate the potential of nutrients in influencing health and wellness.