The leading U.S. pediatricians group is recommending that children receive double the usually suggested 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 vitamin D supplements each day, the American Academy of Pediatrics said. That includes breast-fed infants — even those who get some formula — and many teenagers who drink little or no milk.

Baby formula contains vitamin D, so infants fed only formula 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 do not drink enough of it — four cups daily would be needed — to meet the new requirement, said Dr. Frank Greer, who helped write the report.

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

The advice replaces a 2003 academy recommendation for 200 units daily. That is the amount the U.S. government recommends for people up to age 50; 400 units is recommended for adults ages 51 to 70, and 600 units for those 71 and older.

Vitamin D is sold in capsules and tablets, as well as in drops for young children.

It's also found in cereal and some types of fish, including tuna, mackerel and sardines.

But the best source is sunlight, because the body makes vitamin D when sunshine hits the skin.

The Institute of Medicine, a government advisory group that sets dietary standards, is discussing with federal agencies whether official nutritional recommendations should be changed based on the new research, spokeswoman Christine Stencel said.

The recommendations will be published in the November issue of the academy’s journal, Pediatrics.

Health Canada recommends that all breast-fed, healthy term infants receive 400 IU daily of vitamin D until the infant's diet includes that amount from other dietary sources or one year of age.