The low vitamin D levels -- affecting seven out of 10 children -- may be raising kids' risks for bone problems, heart disease, diabetes and other ailments, a study published in the journal Pediatrics said.
About 9 percent of those ages 1 through 21 -- about 7.6 million children, adolescents and young adults -- have vitamin D levels so low they could be considered deficient, an analysis of federal data by population health Professor Michal Melamed of the Albert Einstein College of Medicine in New York indicated.
An additional 61 percent -- 50.8 million -- have higher levels, but still low enough to be insufficient, she said.
Low vitamin D levels were especially common in children who were older, female, African-American, Mexican-American, obese, drank milk less than once a week, or spent more than four hours a day watching TV, playing video games or using computers, the study found.
The researchers also blamed the low vitamin D levels on children using sunscreen when they do go outdoors, The Washington Post said.
But sunlight exposure to avoid deficiency carries other risks, including skin cancer.
The findings come as the National Academy of Sciences' Institute of Medicine reviews U.S. guidelines for recommended daily vitamin D intake.