Chicago ? The leading pediatricians group in the U.S. says children from newborns to teens should get double the usually recommended amount of vitamin D because of evidence that it may help prevent serious diseases.

To meet the new recommendation of 400 units daily, millions of children will need to take daily vitamin D supplements, the American Academy of Pediatrics said. That includes breast-fed infants – even those who get some formula, too, and many teens who drink little or no milk.

Baby formula contains vitamin D, so infants on formula only generally do not need supplements. However, the academy recommends breast-feeding for at least the first year of life and breast milk is sometimes deficient.

Most commercially available milk is fortified with vitamin D, but most children and teens do not drink enough of it – four cups daily would be needed – to meet the new requirement, said Dr. Frank Greer, the report’s co-author.

The new advice is based on mounting research about potential benefits from vitamin D besides keeping bones strong, including suggestions that it might reduce risks for cancer, diabetes and heart disease. But the evidence is not conclusive and there’s no consensus on how much of the vitamin would be needed for disease prevention.

The new advice, prepared for release today at an academy conference, replaces a 2003 academy recommendation for 200 units daily.

Besides milk and some other fortified foods like cereal, vitamin D is found in oily fish including tuna, mackerel and sardines. But it’s hard to get enough through diet; the best source is sunlight because the body makes vitamin D when sunshine hits the skin.

While it is believed that 10 to 15 minutes in the sun without sunscreen a few times weekly is sufficient for many, people with dark skin and those in northern, less sunny climates need more. Because of sunlight’s link to skin cancer, “vitamin D supplements during infancy, childhood and adolescence are necessary,” the academy’s report says.

Recent studies have shown that many children don’t get enough vitamin D, and cases of rickets, a bone disorder often associated with malnourishment in the 1800s, continue to occur.