In the past few weeks, 3 scientific articles about vitamins caught my eye. Two articles published in the Journal of the American Medical Association reported on findings from the Physicians' Health Study II Randomized Control trial of multivitamins--in the areas of cancer prevention and cardiovascular disease prevention. The third article reported on a survey of Canadian high-performance athletes and their dietary supplement practices.
Multivitamins and Cancer Prevention 
Multivitamins are the most common dietary supplement in the United States, used by as many as 30% of Americans. Data regarding their efficacy in preventing various forms of chronic disease have often been conflicting. As a result, in 2006 a National Institutes of Health consensus conference could offer no specific recommendation regarding the use of multivitamins to prevent chronic disease.
The Physicians' Health Study II is an investigation that involved 14,641 American male physician subjects (mean age, ~64 years) who were randomized to receive either a daily multivitamin or a placebo tablet. Enrollment began in 1999 and follow-up continued for a mean of 11.2 years. At 4 years, the compliance rate (the percentage of subjects still taking the multivitamin or placebo) was approximately 70% and this declined further to approximately 67% by the end of the study period.
Compared with placebo, the subjects taking a daily multivitamin had signficantly fewer total cancers develop during the study period (17.0 vs. 18.3 cancers per 1000 person-years). It appears that multivitamin use did not affect the incidence of new prostate or colon cancers. And despite the findings regarding total cancers, there was no difference in cancer mortality between the 2 groups.
The investigators concluded that daily multivitamin use produced a small but meaningful reduction in cancer incidence. Whether the findings can be generalized to a broader population (including women and younger individuals) is not certain.
Multivitamins and Cardiovascular Disease Prevention 
Also from the Physicians' Health Study II, but reported separately and more recently, the investigators studied several cardiovascular endpoints, including: composite end point of major cardiovascular events (nonfatal myocardial infarction [MI] plus nonfatal stroke plus cardiovascular death) and separate end points of MI or stroke, alone.
The study design was the same as noted above for the multivitamin study.
It turns out that multivitamin use was not associated with a discernible reduction in any of the end points studied. Essentially, a negative study. Again, whether the findings might be generalizable to a broader population is not certain.
Athlete Supplement Survey 
In a 2012 report in the International Journal of Sport Nutrition and Exercise Metabolism, a group of investigators from Calgary reported on a survey that was administered to 440 elite athletes (mean age, ~20 years) from a variety of sports who were affiliated with that country's 8 Canadian Sport Centres. The top 10 sports represented included "athletics," but did not include triathlon or cycling. The represented sports included endurance as well as power sports.
The survey results noted that 87% of athletes had taken at least 3 supplements during the preceding 6 months. The most common supplements were: sports drinks, in 24%; multivitamin and minerals, in 16%; and carbohydrate sports bar, in 11%.
Interestingly, among athletes training 21-25 hours per week, multivitamin use was reported by 63% of athletes and the usage was 59% in those training >25 hours per week.
Athletes reported a variety of sources for their information about supplements, including: family and friends, in 20%; strength trainer, in 14%; and teammates in 11%. Physicians were reported as an information source by only 4% of respondents.
For athletes, there may well be a need for vitamin supplementation and a daily multivitamin is probably the easiest and safest way. The scientific literature regarding mega-dose supplementation with various individual vitamins as well as the relationship between vitamin supplementation and performance remains murky at best. I'm not certain the Physicians' Health Study is particularly applicable to young, healthy athletes, but it appears there might be a small benefit in terms of cancer prevention but no benefit in terms of prevention of cardiovascular disease. Given the complexities of cancer and cardiovascular disease, many authorities would say the findings aren't surprising.
The Canadian athlete survey is interesting because I've seen very little simple reporting on dietary supplementation practices among athletes. It would be fascinating to see such information about age-group participants in running, cycling, swimming, and triathlon. What's clear from the Canadian study is that athletes' information about supplementation may not come from the most authoritative sources and the medical and sports physiology communities could probably do a better job with their educational roles.
1. Gaziano JM et al. Multivitamins in the prevention of cancer in men: the Physicians' Health Study II randomized controlled trial. JAMA 2012;308:1871-1880.
2. Sesso HD et al. Multivitamins in the prevention of cardiovascular disease in men: the Physicians' Health Study II randomized controlled trial. JAMA 2012;308:1751-1760.
3. Lun V et al. Dietary supplementation practices in Canadian high-performance athletes. International J Sport Nutrition Exercise Metabol 2012;22:31-37.