Background: Use of multivitamin and mineral supplements is common among U.S. adults, yet few well-designed trials have assessed the reputed benefits.
Objective: To determine the effect of a daily multivitamin and mineral supplement on infection and well-being.
Design: Randomized, double-blind, placebo-controlled trial.
Setting: Primary care clinics at two medical centers in North Carolina.
Participants: 130 community-dwelling adults stratified by age (45 to 64 years or 
65 years) and presence of type 2 diabetes mellitus.
Intervention: Multivitamin and mineral supplement or placebo taken daily for 1 year.
Measurements: Incidence of participant-reported symptoms of infection, incidence of infection-associated absenteeism, and scores on the physical and mental health subscales of the Medical Outcomes Study 12-Item Short Form.
Results: More participants receiving placebo reported an infectious illness over the study year than did participants receiving multivitamin and mineral supplements (73% vs. 43%; P < 0.001). Infection-related absenteeism was also higher in the placebo group than in the treatment group (57% vs. 21%; P < 0.001). Participants with type 2 diabetes mellitus (n = 51) accounted for this finding. Among diabetic participants receiving placebo, 93% reported an infection compared with 17% of those receiving supplements (P < 0.001). Medical Outcomes Study 12-Item Short Form scores did not differ between the treatment and placebo groups.
Conclusions: A multivitamin and mineral supplement reduced the incidence of participant-reported infection and related absenteeism in a sample of participants with type 2 diabetes mellitus and a high prevalence of subclinical micronutrient deficiency. A larger clinical trial is needed to determine whether these findings can be replicated not only in diabetic persons but also in any population with a high rate of suboptimal nutrition or potential underlying disease impairment.