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What is the problem and what is known about it so far?

People who are malnourished are not able to fight infection as well as people who are well nourished. The ability of the body to fight infection is called immunity or immune function. Some believe that supplementing food intake with vitamin and minerals will improve immune function. Although many people take vitamin and mineral supplements, it is uncertain whether these supplements have health benefits.

Why did the researchers do this particular study?

To find out whether people who take vitamin and mineral supplements have fewer infections and feel healthier than people who do not take supplements.

Who was studied?

130 adults who were at least 45 years old, lived in North Carolina, and had not taken vitamin or mineral supplements during the previous month. Of the 130 study patients, 51 had type 2 diabetes. This is important because people with type 2 diabetes are at risk for vitamin and mineral deficiency and are at higher risk for certain types of infection.

How was the study done?

The researchers assigned patients at random to take either a pill that contained vitamins and minerals or a placebo pill every day for 1 year. The vitamin and mineral pill contained amounts of vitamins and minerals similar to those found in most commercially available multivitamin and mineral supplements. The placebo looked, smelled, and tasted like the supplement but contained only calcium, magnesium, and vitamin B₂. The researchers then followed patients for 1 year and asked them to record in a diary any infections they developed and the number of days they missed work because of an infection. They also asked patients about their physical and mental health, using a standard survey.

What did the researchers find?

Patients taking the placebo pill reported more infections and more days missed from work due to infection than did patients taking the vitamin and mineral pill. This finding was strongest in people who had type 2 diabetes. Of the people with diabetes, 93% of those taking placebo reported an infection compared with only 17% of those taking the vitamin and mineral supplement. Self-reported physical and mental health was similar in both groups.

What were the limitations of the study?

This study did not determine the true nutritional status of the patients, so it is uncertain whether the benefits of the vitamin and mineral supplement were due to its effects on nutrition. In addition, this study included no patients younger than 45 years and only 33 patients over age 65.

What are the implications of the study?

A daily multivitamin and mineral supplement appears to reduce the number of infections, especially in persons with type 2 diabetes, a group that is at risk for vitamin and mineral deficiencies.