New studies have found it may help reduce risks of cancer, diabetes and heart disease, in addition to keeping bones strong.
Those studies mean that many American children, like David Osorio, are Vitamin D deficient, reports CBS News medical correspondent Dr. Jon LaPook. Osorio is only six-years-old and has already suffered bone fractures in both arms.
"I fell off the slide and first I broke this wrist," Osorio said cradling his left arm in his right hand.
But the root cause of those broken bones is more than a boisterous boy at play, LaPook reports, it's also a serious lack of Vitamin D.
"It's a very preventable thing if you're up on your nutrition - it seems easy enough to supplement with Vitamin D rather than suffer the consequences of having a broken bone," says Dr. Shevaun Doyle.
The new advice replaces a 2003 academy recommendation for 200 units daily.
That's the amount the government recommends for children and adults up to age 50; 400 units is recommended for adults aged 51 to 70 and 600 units for those aged 71 and up. Vitamin D is sold in drops for young children, capsules and tablets.
"New research is showing that you need to at least double that in order to not only fight off the old diseases like rickets (which is a bone disease) and osteomalaysia, but we're looking at diabetes and heart disease and even cancer," Dr. Ian Smith told CBS' The Early Show.
To meet the doctors' new recommendation of 400 units daily, millions of children would 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 to meet the new requirement, said Dr. Frank Greer, the report's co-author.
The report does not recommend getting the extra vitamin D from eating more food containing the vitamin, because of the amount of food one would have to consume.
"For example, if you are a child, you'd have to drink four cups of fortified milk in order to get your recommended 400 units," Smith said. "Most children and teenagers are not drinking four cups. So what you have to do is figure out whether or not you can get a combination of milk, fortified cereals or oily fish, such as tuna, mackerel or sardines."
Since it is difficult to get enough Vitamin D through diet alone; 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, people with dark skin and those in northern, less sunny climates need more. Because of sunlight's link with skin cancer, "Vitamin D supplements during infancy, childhood and adolescence are necessary," the academy's report says.
Can one have too much vitamin D in their diet?
Smith says yes, but that is rare, "because the amount you have to consume is outrageous. Ninety-five percent of the people who are consuming the average diet, who are getting the average exposure to sunlight will not have too much vitamin D in their system."
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.
Christine Stencel, a spokesperson for the U.S. Institute of Medicine, which sets recommended daily doses of nutrients, says it's been several years since they looked at revising the recommendation for Vitamin D and it may now be time.
"The Institute of Medicine would stand ready to do a new review of all the scientific evidence about Vitamin D intakes," she told CBS News.
The recommendations were prepared for release Monday at an academy conference in Boston. They are to be published in the November issue of the academy's journal, Pediatrics.
Dr. Greer, a University of Wisconsin pediatrician, acknowledged that most studies suggesting vitamin D may play a much broader role in disease prevention have been observational, not the most rigorous kind of medical evidence.
Nonetheless, many doctors consider the research compelling and many have begun to offer patients routine vitamin D testing.
Adrian Gombart, a vitamin D researcher at Oregon State University, said the new recommendations are safe and conservative but that 400 units "is probably not enough."
Gombart's lab work in human tissue has shown that vitamin D helps increase levels of a protein that kills bacteria. He said many experts believe that between 800 and 1,000 units daily would be more effective at helping fight disease.
Several members of an academy committee that helped write the guidelines have current or former ties to makers of infant formula or vitamin supplements.