Multivitamins, heart disease, and cancer
The USPSTF review panel was interested in the literature on certain supplements taken alone, paired, and in multivitamins (combinations of three or more). These included:
Vitamins: folic acid, beta-carotene, vitamin A, thiamine (vitamin B1), niacin (vitamin B3), riboflavin (vitamin B2), vitamin B6, vitamin B12, vitamin C, vitamin D, and vitamin E
Minerals: calcium, iron, zinc, magnesium, and selenium
After reviewing the medical literature, 26 studies that were the source of 103 published research articles were judged to be of “fair” or “good” quality under USPTF quality criteria guidelines and were included in the review.
What did they find?
Taking a multivitamin for ten or more years may reduce cancer risk in men by approximately 6%, but had no effect on cancer risk in women. None of the research supported benefits or harms of vitamin and mineral supplements for heart disease prevention.
As has been known for over a decade, beta-carotene supplements were found to increase lung cancer risk in smokers. Fortunately, knowledgeable healthcare professionals have been advising smokers to avoid beta-carotene supplements for many years.
What does it all mean?
Because the panel concluded that vitamin and mineral supplements have limited evidence to support they prevent cancer or cardiovascular disease, the media has been quick to proclaim supplements useless. However, people take supplements for a wide range of health goals, many of which have been well demonstrated in research. For example, for osteoporosis, we would focus on particular nutrients, such as vitamins D and K, calcium, and magnesium. Further, the benefits of correcting deficiencies, which are common in certain regions or demographic groups, are also well-known. In most cases, the authors point out, we still don’t have enough good quality research on most combinations of vitamins and minerals to come to any solid conclusions about health benefits or harms. Here are some reminders for how this latest information on vitamin and mineral supplements fits into the larger discussion on vitamin and mineral efficacy:
- Consider synergy. As noted by the panel, the complexity of the human body could be one reason why supplementing one or two nutrients alone appears to be ineffective, or even harmful. The multivitamin studies did show benefits, so for general health, consider a balanced multivitamin instead of large doses of single nutrients.
- Look at individual needs. These results don’t address specific health goals. Work with your doctor or a registered dietitian to define your health goals, and how best to meet them.
- Look at all the research. This type of study compares studies of varying designs and, in this case, specific supplements and two specific health conditions, which eliminates research that may show a range of results for other health conditions and nutrients.
- Assess underlying health. The review focused on healthy older adults with no nutrient deficiencies. Supplements may benefit younger people, or those eating a poor diet, or with compromised nutritional status for other reasons, such as an existing illness or an inability to consume a varied diet.
- Tune out nutritional “fear-mongering.” Previous observational studies suggested harm from multivitamins; however, controlled clinical trials—the gold standard of evidence—found no health harm. The current review even suggests protection against cancer for men. Avoid the fear-mongering headlines, and ask a qualified health professional to help you sort fact from fiction.
- Don’t go on faith alone. Sometimes the hype about dangers can make people reject all cautions on supplement use, some of which should be observed. Though often natural, supplements still affect body chemistry and should be used carefully and with some education, especially if you are also using medicine to manage a health condition. And of course, if you are a former or current smoker, ask your doctor or dietitian before you use higher doses of any nutrient and avoid beta-carotene to avoid increasing cancer risk.
(Anl Intern Med 2013, online ahead of print; available at: annals.org/article.aspx?articleid=1767855)