Nutritional supplements and infection in the elderly: why do the findings conflict?

Nutrition Research Newsletter, Dec, 2006

About 40% of the elderly in the United States take multivitamin-mineral supplements, and their use is increasing. Studies of the clinical outcomes of such use therefore have important health and economic implications, especially as the outcomes are expected to depend on supplement constituent dosages. As shown in a recent meta-analysis, studies that examine the clinical effects of such supplements on the health of the elderly have had sharply conflicting results. The studies they considered were randomized placebo-controlled trials that examined the effects of multivitamin-mineral supplements on infection in the elderly. In most studies the participants were community-dwelling. Five of the trials showed either negative or nonsignificantly positive effects, as did an additional trial of the same type, published after their analysis. However, dramatic benefits were reported in the three remaining studies. In each of these positive studies, which lasted a full year, the number of days of infection (NDI) in the supplement group was reported to be approximately half of the NDI in the placebo group. Averaged over members of the supplement groups, this indicates that the treatment reduced their NDI by about twenty days during the treatment year. Especially given the growing proportion of elderly in our population, the increasing age of retirement, and the ballooning costs of health care, such dramatic benefits would have enormous economic and quality-of-life implications. The purpose in the present paper was to comment briefly on the validity of the first of the positive reports, and to evaluate the other two, which can be regarded as reporting successful attempts to replicate the first. The possibility that trials such as these may influence decisions about required dietary allowances increases the importance of assessing their validity.

Examination of internal consistency (outcomes of statistical tests versus reported data); comparison of variability of NDI across individuals in these two reports with variability in other trials; estimation of the probability of achieving the reported close agreement with the original finding. The standard deviations of NDI and levels of statistical significance reported are profoundly inconsistent. The reported standard deviations of NDI are consistently below what other studies have found. The reported percent reductions in NDI agree too closely with the original study.

The claims of reduced NDI in the two replication reports should be questioned, which also adds to concerns about the 1992 study. It follows that there is currently no trustworthy evidence from randomized placebo-controlled clinical trials that favors the use of vitamin-mineral supplements to reduce infection in the elderly.

S Sternberg, S Roberts. Nutritional Supplements and Infection in the Elderly: Why Do the Findings Conflict? Nutr J; 5:30 (November 2006). [Correspondence: Saul Sternberg Department of Psychology, University of Pennsylvania, Philadelphia, PA 19104-6228.]