Effect of Supplementation With Multivitamins and Minerals on the Incidence of Respiratory Infections in Older People in Ecuador: a Randomised Controlled Trial.

Even "subtle subclinical deficiencies of micronutrients and inadequate macronutrient intake contribute to a decline in immune function in the elderly" [1]. "The impaired regulation of the immune system in aging contributes to a higher morbidity and mortality from infections, autoimmune, and neoplastic diseases"[1]. Some studies show that either vitamins or minerals supplements may improve the immune function in older subjects [2-5 ]. Therefore, it is plausible to assume that improvement of their nutritional status through MVM supplements may benefit their ability to fight infections. The hormonal and physiological deregulation in aging might also benefit from MVM adding to the body effectiveness to deal with common pathogens in aging.

A previous systematic review and meta-analysis of randomised controlled trials (RCT), which included papers published before January 2004, found no evidence of an effect of MVM supplementation on infection rate [6] or duration [7] in older people. However, considerable clinical and methodological heterogeneity was present in the studies included in this earlier review. The investigators have updated this earlier systematically review of the evidence that MVM supplementation is effective in reducing the incidence of infection in older people. Sub-group analysis explored the effect site of residence (nursing homes or dwellings) of study participants, primary outcome measure (self report or clinical evaluation), and baseline micronutrients status of enrolled subjects [8].

The investigators found no evidence of benefits from multivitamin and minerals supplementation on the rate of infection or the odds ratio of infection in aging subjects. The investigators also found no benefit of intervention in the subgroups analysed. Sensitivity analysis of those studies evaluated as free of bias did not substantially alter this conclusion.

The included trials were heterogeneous in sample size (range 33 to 2799), duration (range 4 to 24 months), and outcome measures. The lack of benefit of the intervention in studies which found variable percent of subjects with some micronutrient deficiencies at enrolment could be related to some characteristics of the included trials: All studies but that of Avenell [9] had not determined the micronutrients status of the target population before the enrolment. Therefore, the formulas of multivitamin and mineral supplements used were not aimed to correct any pre-specified deficiency. Moreover, those studies had different considerations to define the formula, which explains the large variability of the supplements across the studies. Finally, the assessment of the micronutrient status was also variable across the studies: dietary intake evaluation and/or micronutrients blood concentration, which affects the consistency of this subgroup meta-analysis.

It is noteworthy that all studies except one [10] have been carried out in developed countries where the nutritional status of aging populations seems to be better than that reported by studies carried out in developing countries. In fact, although the variability of the assessment methods do not allow to draw a clear conclusion on the baseline nutritional status of the subjects included in the analysed studies, the prevalence of deficiencies and the number of micronutrients found deficient are evidently lower than those referred in studies from developing countries such as those carried out in Ecuador [11]. The remaining study was carried out in a middle-income country and although data on baseline nutritional status of enrolled subjects was not published, presumably their micronutrient status is somehow similar to that found in developed countries.