Vitamins are often taken by the people who need them least, a new study suggests.
The study showed that people who take mineral supplements also to get more nutrients from their food than those who don't take supplements.
Indeed, in some cases, supplement users may be getting too much of a good thing by overloading on minerals, such as iron, that can cause potentially serious health problems, researchers said.
Regan Bailey, a nutrition researcher at the National Institutes of Health, and her colleagues used dietary surveys to assess mineral intake among 8,860 men and women who participated in a major government health survey between 2003 and 2006.
Women take more supplements
Men and women who reported using dietary supplements containing eight minerals (calcium, iron, magnesium, zinc, phosphorus, copper, potassium and selenium) were much less likely to be getting inadequate amounts of those minerals from the foods they ate compared to people who said they didn't take supplements.
The link was strongest for women, who are more likely than men to take supplements.
Supplement users, in turn, tend to eat better and live healthier lifestyles than nonusers, Bailey noted in an email to Reuters Health.
The NIH team also found that calcium intake often fell below recommended levels, even among professed supplement users, the researchers reported online on September 28 in The American Journal of Clinical Nutrition.
Users go over the limit
Roughly 25% of supplement users, and 71% of nonusers, did not receive the recommended daily amount of calcium (800 to 1,000 mg for men over age 51 and 1,000 to 1,200 mg for women of the same age).
Older people were much more likely to fall short of their daily calcium requirements – and also to exceed them. Nearly 16% of women between the ages of 51 and 70 reported daily calcium intakes that exceeded the recommended upper limit.
Supplement users also were more likely to boost their intake of magnesium and zinc above recommended upper limits.
Dietary assessment is good
Cheryl Rock, a nutrition researcher at the University of California, San Diego, said the results are not surprising in light of previous research, including her own, into the dietary habits of supplement users. "We always hope that the people who are taking dietary supplements are the ones who need it the most, but it doesn't seem to be true," Rock said.
When it comes to overconsumption, Rock added, "We have been telling people clinically for years that the daily value cut point is not your minimum requirement. "Having a dietary assessment is definitely a good idea to determine where one's nutrient intake might be inadequate, if at all," she said.
The National Institutes of Health provides information on nutritional supplements: http://1.usa.gov/pCsLJt.
(Reuters Health, October 2011)