Skeptical Raptor's Blog hunting pseudoscience in the internet jungle

Multivitamins–big money, no effect on cardiovascular disease

A few months ago, I wrote about the role of supplements, mainly vitamins and other nutrients, in preventing cancer. Conclusion: they didn’t. To quote Martinez et al., who published a review of dietary supplements and vitamins in cancer prevention

Nutritional supplementation is now a multibillion-dollar industry, and about half of all US adults take supplements. Supplement use is fueled in part by the belief that nutritional supplements can ward off chronic disease, including cancer, although several expert committees and organizations have concluded that there is little to no scientific evidence that supplements reduce cancer risk. To the contrary, there is now evidence that high doses of some supplements increase cancer risk. Despite this evidence, marketing claims by the supplement industry continue to imply anticancer benefits. Insufficient government regulation of the marketing of dietary supplement products may continue to result in unsound advice to consumers. Both the scientific community and government regulators need to provide clear guidance to the public about the use of dietary supplements to lower cancer risk. 

All those expensive supplements, most of which have broad and unproven claims made about them, do precious little for cancer. And some actually increase the risk of certain types of cancer.

In 1997, a large-scale, randomized, double-blind, placebo-controlled trial (called the “Physicians’ Health Study II”, or PHS II) commenced with 14,641 male US physicians initially aged 50 years or older, and included including 754 men with a history of cardiovascular disease (CVD) at randomization. These men were enrolled in a common multivitamin study with treatment and follow-up through June 1, 2011. They were randomized to either a daily multivitamin or a placebo.

Over a follow-up period of an average of 11.2 years, 1,732 cardiovascular events were reported. However, the rate of events was no higher among the placebo group than the daily multivitamin group. The major cardiovascular event rates were 11 and 10.8 per 1000 person-years in the multivitamin and placebo groups, respectively.

According to an article in Heartwire by Shelley Wood, “looking at components of the primary end point individually and a range of secondary end points, Sesso and colleagues found no statistically significant differences in rates of MI, all stroke, hemorrhagic stroke, ischemic stroke, congestive heart failure, angina, coronary revascularization, CVD mortality, or overall mortality. An additional analysis, which excluded the first few years of follow-up (to allow for a cumulative effect of exposure), did not alter the results. No major differences in adverse effects were seen between groups.”

The PHS II investigators acknowledged that multivitamin supplements have an important role in groups who have nutritional deficiencies, but PHS II did not investigate such groups. In addition, the physicians included in the PHS II study were “quite healthy,” according to the study’s lead author, Howard Sesso. The study participants mostly exercised regularly, ate reasonably well, and didn’t smoke. Sesso et al. wrote that the group “likely represent, on average, a well-nourished population who already have adequate or optimum intake levels of nutrients, for which supplementation may offer no benefits.”

In JAMA’s accompanying editorial, Eva Lonn wrote that over one-third of the US population takes some kind of daily multivitamin, which makes dietary supplements an almost $24 billion industry in 2008. As a result of the  Dietary Supplement Health and Education Act of 1994, the FDA’s regulation of supplement approval, labeling and marketing is less strict than for drugs.

Lonn argued that:

…this has allowed for claims of benefit in preventing or curing an amazingly diverse and ever-increasing variety of illnesses ranging from CVD to cancer, arthritis, infections, macular degeneration, Alzheimer’s disease, wrinkles, hair loss, decreased libido, and low sexual prowess. As a result, many people with heart disease or risk factors continue to lead unhealthy lives yet take daily vitamins and supplements in the hope of mitigating future problems.

This distraction from effective CVD prevention is the main hazard of using vitamins and other unproven supplements. The message needs to remain simple and focused: CVD is largely preventable, and this can be achieved by eating healthy foods, exercising regularly, avoiding tobacco products, and, for those with high risk-factor levels or previous CVD events, taking proven, safe, and effective medications.

Though this study showed that regular multivitamin use has no effect on CVD, it’s important to remember that these men were mostly healthy. It is possible that supplement use in an unhealthy population might prove beneficial, but it might be difficult to separate out the supplement’s usefulness in proper nourishment from any benefits to preventing CVD. But it’s clear that other factors, such as maintaining proper weight and not smoking, have a higher impact on CVD rates than multivitamins do. And unless there is some dietary issue about consuming a balanced diet, supplements will have little or no effect on CVD.

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