CHICAGO - About a third of U.S. children and teens take vitamins, even though most of those taking the pills are healthy, active kids who probably don’t need them, a new study suggests.

Youngsters who could benefit the most from vitamins - kids in fair or poor health with the worst eating habits - were the least likely to take them, researchers reported.

The survey of parents of children aged 2 to 17 was done from 1999-2004. The results show a decline in vitamin use from the 1970s when roughly half of all American children took vitamins, the study’s lead author said.

The study highlights a question doctors often get from parents: Should I give my kids vitamins?

The study’s lead author, Dr. Ulfat Shaikh, a pediatrician at the University of California-Davis Children’s Hospital in Sacramento, says taking daily multivitamins in the dose recommended on the label probably is harmless. However, they often aren’t needed for healthy children with a varied diet, she said.

Also, some parents and teens may mistakenly think taking a daily pill will make up for a lousy diet, Shaikh said. Pediatricians generally agree that the best source for vitamins and minerals is a varied diet that includes fresh fruit, vegetables and fiber - not pills.

The new study, released Monday in the February issue of Archives of Pediatrics & Adolescent Medicine, asked about use of vitamin and mineral supplements in general, not about specific ones including vitamin D. It found supplement use was most common among frequent milk drinkers and those with varied diets - children who likely are meeting the academy’s latest recommendations.

Dr. Ronald Kleinman, editor of the pediatrics academy’s nutrition handbook, said the study bolsters previous evidence that children who may need vitamins the most don’t take them.

“Most of us would do that by recommending a better meal plan” rather than vitamin supplements, he said.