1. Studies of single and paired nutrients did not show a clear benefit in preventing cardiovascular disease (CVD) or cancer, but also do not have appreciable adverse effects.
2. Pooled results from two large trials reported lower cancer incidence in men taking a multivitamin for more than 10 years, however the effect was small and not significant in women.
Evidence Rating Level: 1 (Excellent)
Study Rundown: Vitamins and minerals are commonly used by patients to prevent chronic disease and promote health, with nearly half of the U.S. population reporting use of a dietary supplement. In vitro and animal studies have shown that supplements may protect against CVD and cancer by reducing cellular damage, however studies in humans have been equivocal at best. In 2003, the U.S. Preventive Services Task Force (USPSTF) concluded that there was insufficient evidence to recommend for or against the use of vitamins A, C, and E, multivitamins with folic acid, or antioxidant combinations for the prevention of CVD or cancer. Further, they recommended against the use of B-carotene supplements given evidence that these products may actually increase risk for developing lung cancer in vulnerable individuals.
The current study reviewed additional evidence on the use of vitamin and mineral supplements among the general adult population in order to help the USPSTF update their recommendation statement. The authors concluded that there is still limited evidence to support any benefit from the use of vitamin and mineral supplementation for the prevention of cancer or CVD. Additionally, findings continue to show that B-carotene increases lung cancer risk in susceptible adults. The conclusions are limited by the fact that only primary prevention studies in adults without known nutritional deficiencies were used in the analyses. Additionally, the duration of most studies was less than 10 years. Nonetheless, the study conclusions are in line with the previous USPSTF recommendations on the use of vitamin and mineral supplements in non-deficient adults.
In-Depth [meta-analysis]: Randomized, controlled trials and cohort studies that assessed the effectiveness or safety of supplements in the primary prevention of CVD, cancer, or all-cause mortality in the general adult population were included in the analysis. Studies were included if participants were community-dwelling, nutrient-sufficient adults without chronic disease or history of CVD or cancer who lived in developed countries. The studies selected investigated the benefits and harms of multivitamin supplementation, individual or paired supplements, B-carotene, vitamin E, selenium, vitamin A, vitamin C, folic acid, vitamin D, calcium, or vitamin D and calcium in combination. Study results were stratified by supplement, and meta-analyses were conducted to estimate the effect size of supplementation on CVD incidence, cancer incidence, and all-cause mortality at the longest follow-up time point of each study. Unadjusted relative risks were calculated based on the number of events and nonevents.
26 studies (24 randomized, controlled trials and 2 cohort studies) were included in the analysis. In the studies of single and paired nutrients (including vitamins A, C, or D, folic acid, selenium, or calcium), there was little evidence to support or refute an effect on all-cause mortality, incidence of CVD, or cancer among patients. B-carotene also had no effect on these variables, however there was a probable increase in lung cancer incidence in high-risk subgroups, such as smokers and asbestos workers. In trials looking at multivitamins, there was no effect on fatal and nonfatal CVD events overall. One large trial did show a reduction in overall cancer incidence after 11.2 years of follow-up, while another showed a protective effect among men (adjusted relative risk, 0.69 [95% CI, 0.53 to 0.91]) but not among women. Taken together, these two trials (n = 27,658) reported lower overall cancer incidence in men taking a multivitamin for more than 10 years (pooled unadjusted relative risk, 0.94 [95% CI, 0.89 to 1.00]).
By Sarah Chuzi and Aimee Lee, MD
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