About 20% of US adults take a daily multivitamin and mineral supplement. While there is strong evidence that supplementing with certain vitamins can reduce the risk birth defects, there is far less compelling evidence that multivitamin and mineral supplements can prevent chronic diseases like coronary heart disease and cancer.

The benefits of multivitamin and mineral supplements in reducing the risk of infection have long been debated. Although it is certainly plausible that mild nutrient deficiencies could impair immune function, clinical trials of micronutrient supplements in elderly people—who are vulnerable to nutritional deficiency—have produced conflicting results.

Researchers from the University of North Carolina School of Medicine and Wake Forest University School of Medicine decided to investigate further. In a paper published in the March 4, 2003 Annals of Internal Medicine , they report that a multivitamin and mineral supplement did in fact reduce the risk of infection, particularly in people with type 2 diabetes .

About the Study

The researchers enrolled 130 people aged 45 and older, who had not taken vitamin or mineral supplements during the previous month. The study participants were divided by age (45 to 64 years; 65 and older) and diabetes status (presence or absence of type 2 diabetes). This was done because increasing age and presence of diabetes can increase the risk of micronutrient (vitamin and minerals) deficiencies.

The researchers then randomly assigned the patients to receive treatment or placebo. Treatment consisted of a daily tablet containing beta-carotene and the vitamins A , B1 (thiamin) , B2 (riboflavin) , B3 (niacin) , B6 , B12 , C , D , E , K , biotin , pantothenic acid, and folic acid and the minerals calcium , magnesium , manganese , copper , iron , zinc , iodine, selenium , and chromium . This micronutrient composition was very similar to that found in most commercially available multivitamin and mineral supplements. The placebo group received a daily oral tablet containing only calcium, magnesium, and vitamin B12. The placebo was designed to look and smell similar to the treatment pill.

Participants filled out food diaries at the beginning of the study and at six months. Researchers used this data to determine nutrient deficiencies, defined as intake below the 33rd percentile of the recommended daily allowance (RDA) for that nutrient.

The study participants noted any symptoms of infectious illnesses (upper or lower respiratory tract infection, influenza-like syndrome, gastrointestinal infection, and urinary tract infection ) they contracted over the course of the one-year study. They also noted whether those infections resulted in “absentee days”—days missed from work or the inability to perform planned activities.

The Findings

Participants with type 2 diabetes were more likely than participants without type 2 diabetes to be deficient in one or more micronutrient (33% versus 19%).

Study participants taking a placebo reported more infections than the group taking a daily multivitamin and mineral supplement (75% versus 43%). 57% of the placebo group reported infection-related absenteeism compared to 21% of the treatment group.

Of the participants with type 2 diabetes, 93% of those taking a placebo reported an infection, compared with only 17% of those taking a daily multivitamin and mineral supplement. In this population, 89% of the placebo group reported infection-related absenteeism, compared to 0% of the treatment group.

There were no other statistically significant differences between study participants in different age categories.

Two important limitations of the study were its small sample size (130 participants) and the fact that many study participants correctly guessed whether they were receiving treatment or placebo.

How Does This Affect You?

This study suggests that if you have type 2 diabetes, you are more likely to be deficient in certain micronutrients and that taking a daily multivitamin and mineral could reduce your risk of infection. However, given the limitations of the study and the long and controversial history of micronutrient research, this is certainly not the final word on the subject.

Nevertheless, until larger trials are done, you may wish to consider adding a micronutrient supplement to your daily routine. They are convenient, relatively inexpensive, generally safe if taken as directed, and may actually help protect you from some mild infections.