A new study has found supplements did little to help healthy adults ward off illness, but supplements did help diabetics avoid respiratory and gastrointestinal infections and flu-like illnesses.
About 40 percent of U.S. adults take a vitamin supplement regularly, says study author Dr. Thomas Barringer, director of research in the family medicine department at Carolinas Medical Center in Charlotte, N.C. Yet previous research has found little evidence to show that taking a multivitamin helps prevent illness.
Barringer and his colleagues divided 130 people aged 45 and older into two groups. Half were given a daily supplement containing 23 vitamins and minerals. The other half were given a placebo that contained only calcium, magnesium and vitamin B12, so the pill looked and smelled the same as a multivitamin.
The study found only 43 percent of people taking a multivitamin got an infection during the year, compared to 73 percent of those on the placebo. However, those numbers are misleading, Barringer says: All of the difference in infection rates was among those with diabetes.
When the diabetics' rate of infection was calculated separately, researchers found that only 17 percent of diabetics in the multivitamin group got an infection, compared to a whopping 94 percent of those on the placebo.
For non-diabetics, the rate of infection was nearly identical in both groups: 59 percent for the multivitamin group and 60 percent for the placebo group. "There was no benefit in the non-diabetic group," Barringer says.
The study appears in the March 4 issue of the Annals of Internal Medicine.
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"At this point, there is still very little data to support supplements in healthy, non-elderly adults," Barringer says.
Wafaie Fawzi, an associate professor of international nutrition and epidemiology at the Harvard School of Public Health, says it's too soon to give up on multivitamins.
Multivitamins are relatively inexpensive, and there's little risk to taking one, says Fawzi, who wrote a commentary about the study.
"The study provides preliminary evidence that micronutrients may be important for reducing the risk of infections among adults in the U.S., especially those at higher risk such as diabetes," he says. "The evidence is not conclusive in that regard and further trials are warranted."
Diabetes can leave people prone to infections because out-of-control blood sugar compromises the immune system, Barringer says. Poorly controlled diabetes can also lead to minor deficiencies of certain minerals that are lost in excessive urination.
While the reduction in infections among diabetics sounds dramatic, it's possible not all diabetics would need a multi-vitamin, Barringer says.
The diabetics in the study were from a lower socioeconomic group than the non-diabetics, he says. People who have less education and are poorer are more likely to have nutritional deficiencies.
Barringer wanted to conduct his vitamin test on people aged 65 and older because the elderly can also be prone to minor nutritional deficiencies. But he couldn't find enough willing to take part in the study.
"They were all taking multivitamins already, and nobody was willing to stop taking them for a year," Barringer says. "I beat my head against the wall trying to find people."