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Dr. Michael F. Holick, professor of medicine, physiology and biophysics and director of the Vitamin D, Skin and Bone Research Laboratory at the Boston University School of Medicine, said that "we estimate that vitamin D deficiency is the most common medical condition in the world."

"Children should take vitamin D supplements and be less afraid of sensible sun exposure," Holick said.

"At a minimum, from the time a child is born, they should be on 400 IU of vitamin D a day," he said. "After the age of 1, they should be up to 1,000 IU per day, and teenagers should definitely be on 2,000 IU a day."

Holick would prefer to see the safe upper limit of vitamin D raised. "What I would recommend is that in the first year of life, it should be raised to 5,000 IU per day and for children over the age of 1 and all adults, 10,000 IU a day," he said.

More information

For more information on vitamin D, visit the Nemours Foundation.

SOURCES: Jonathan Mansbach, M.D., assistant professor of pediatrics, Harvard Medical School and Children's Hospital Boston; Samantha Heller, R.D., C.D.N., registered dietitian, clinical nutritionist, exercise physiologist, Fairfield, Conn.; Michael F. Holick, Ph.D., M.D., professor of medicine, physiology and biophysics,director, Vitamin D, Skin and Bone Research Laboratory, Boston University School of Medicine; November 2009, Pediatrics