MONDAY, Oct. 13 (HealthDay News) -- The leading children's medical organization in the United States on Monday announced that it has doubled the amount of vitamin D recommended for infants, children and adolescents.

The increase, from 200 international units (IU) to 400 IU per day, starting in the first few days of life, was detailed in a news conference at the annual meeting of the American Academy of Pediatrics (AAP), in Boston. The new recommendations were expected to be published in the November issue of Pediatrics.

"Four hundred IU a day is the amount that is in a teaspoon of cod liver oil, which we have used for 75 years to prevent and treat rickets in children and, historically speaking, that is the amount that is in any chewable multivitamin tablet and in any liquid preparation for infants," said Dr. Frank Greer, a lead author on the report and chairman of the AAP National Committee on Nutrition.

In fact, Greer added, today's supplements already carry a minimum of 400 IU of vitamin D.

"Four hundred is probably the minimum," said Dr. Don Wilson, a professor of pediatrics at Texas A&M Health Science Center College of Medicine and a pediatric endocrinologist with Scott & White.

Certain risks associated with vitamin D deficiency have been known for decades: rickets (weakening of the bones), which is still widespread in infants, children, adolescents and adults; growth failure; lethargy; irritability; respiratory infections during infancy; and osteoporosis later in life.

More recently, however, associations have been made between vitamin D deficiency and type 2 diabetes, some cancers, multiple sclerosis and rheumatoid arthritis.

"Among rheumatologists who treat patients with autoimmune diseases, there has been an increasing recognition that insufficiency in vitamin D may contribute to a variety of autoimmune diseases," said Dr. Nora G. Singer, a pediatric rheumatologist at Case Western Reserve University's Rainbow Babies and Children's Hospital, in Cleveland. "If [vitamin D deficiency] really does impact innate immunity or the first line of immune defense, then maybe some of the increase in autoimmune diseases we're seeing could relate to this."

Vitamin D, according to Greer, is not actually a vitamin at all but a hormone. "It acts directly on cells to promote gene transcription," he explained. "No other 'vitamin' does this, so it really is very, very powerful."

Vitamin D deficiency is common among all age groups across the globe.

The main source of vitamin D is sunlight but experts now urge everyone to stay out of the sun or, at the very least, to wear sunscreen and protective clothing while outside.

Vitamin D is not plentiful in most foods, with the exception of fatty fish, certain fish oils, liver and egg yolks of chickens fed vitamin D.

"We know 400 IU a day is safe and prevents rickets," Greer said. "We don't have any idea if that amount of vitamin D is enough for other diseases. We also don't know if anything over 400 is safe."

Here are the AAP's recommendations:

• Infants who are breast-fed or partially breast-fed receive 400 IU a day of vitamin D in supplements, beginning in the first few days of life. Many mothers are deficient in the vitamin and pass this on to their newborns. Supplementation should be continued unless the infant starts taking at least one quart a day of vitamin D-fortified formula or whole milk, although whole milk should not be introduced until the child has turned 1. Many children, including those with a family history of obesity, should only be drinking low-fat milk.
• Non-breast-fed children and older children should also receive a vitamin D supplement of 400 IU/day.
• Children at increased risk of vitamin D deficiency (for example, those taking anti-seizure medications) may need higher doses, but this should only be done in consultation with a health-care professional.

More information

The Office of Dietary Supplements has more on vitamin D.