The sunshine vitamin is in the spotlight again -- and this time the focus is on infants and toddlers.
Many young children do not get enough vitamin D, one team of researchers said. And while experts agree on the problem, the solution is another matter.
In a study at Children's Hospital Boston, researchers found that 12 percent of infants and toddlers were deficient in vitamin D and 40 percent had below-optimal levels.
The findings, published in the June 2008 issue of Archives of Pediatrics & Adolescent Medicine, also showed that one-third of children who were deficient had changes in bone density seen on X-rays of the wrist and knee. A few even had signs of rickets, or softening of the bones caused by severe deficiency of vitamin D.
"We didn't pick up a lot of rickets, but we did pick up a lot of vitamin D deficiency," said Dr. Catherine Gordon, director of the Bone Health Program at Children's Hospital Boston and one of the study's co-authors. "We need to be concerned."
In 2004, Gordon and her colleagues found that 42 percent of adolescents were vitamin D deficient. This led them to wonder whether the problem began during childhood.
"I think these data suggest that vitamin D deficiency is common throughout the age spectrum now," Gordon said about the latest results.
Vitamin D is crucial for bone growth and calcium absorption in the intestine. It also plays a role in regulating the immune system.
The sun is the best source of vitamin D; ultraviolet rays trigger its production in the skin. Parents routinely cover young children with sunscreen, blankets or additional layers of clothing to protect them from harmful UV rays, so children may not have enough sun exposure to produce sufficient levels of vitamin D.
Diet is another source of the vitamin. Few foods naturally contain vitamin D, but milk products, bread and cereals are often fortified with it.
As expected, infants fed with enriched formulas and toddlers who routinely drank milk were more protected from vitamin D deficiency, and breast-fed infants who did not receive vitamin D supplements were at a higher risk.
"Breast milk is the perfect food," Gordon said. "It's the healthiest way to feed an infant, but it has been shown to be deficient in vitamin D."
The American Academy of Pediatrics recommends that infants and children receive a minimum of 200 international units of vitamin D daily, starting during the first two months of life and continuing through childhood and adolescence.
Most formulas provide the daily recommended value, but breast milk does not. To compensate, breast-fed infants can be given a liquid multivitamin drop that contains vitamin D.
In light of these findings, Gordon said that routine supplementation of infants and children is a safe and cost-effective measure for correcting vitamin D deficiency.
Some doctors agree.
"There is every reason to supplement with vitamin D and no reason not to," said Dr. Robert Lustig, professor of clinical pediatrics at the University of California at San Francisco.
Lustig points out that the cost of supplementation presents a challenge, though. Vitamins are not considered medicines, and are generally not covered under health insurance policies.
Other experts worry about the potential harm that could result if children consume excess vitamin D. Like vitamins A and E, vitamin D is fat-soluble, so it is stored in the body's fat cells instead of eliminated in the urine. According to the National Institutes of Health, too much vitamin D can cause nausea, vomiting, constipation and weakness.
"Meeting the need is great, but exceeding the need is not always good," said Madelyn Fernstrom, professor and director of the UPMC Weight Management Center in Pittsburgh. "Especially with infants and toddlers, I think we should proceed with caution."
Keith Ayoob, associate professor of pediatrics at Albert Einstein College of Medicine in New York, agrees that routine supplementation is unnecessary at this point.
"The first line of defense is to find out why kids are not getting enough vitamin D and correct that," he said.
Ayoob and Fernstrom suggest that this deficiency is primarily a lifestyle problem, resulting from the fact that children are not consuming enough vitamin D to meet the guidelines.
"It doesn't matter how great a recommendation is if a parent is not using it," Fernstrom said.
In the study, low vitamin D levels were linked to lack of milk intake for many of the children. Therefore, Ayoob said dietary deficiencies should be addressed first.
"If you supplement them, they're still going to have a bad diet," he said. "They're going to have a very well-supplemented bad diet."
Fernstrom suggests a few simple changes that might remedy the problem: Giving toddlers vitamin-D fortified milk instead of juice and making sure at least a small part of the body, such as the hands or legs, are exposed to sunlight for about 30 minutes a day.
Experts do agree that one group should be routinely supplemented: infants who are breast-fed, as breast milk just doesn't have enough vitamin D.
The next step? Dr. James Taylor, professor in the department of pediatrics at the University of Washington, said a long-term study is needed to determine the lasting effects of vitamin D deficiency on infants and toddlers. Researchers should also look at whether supplements have positive effects on bone density.
"There's a lot of research on vitamin D right now," Taylor said. "I think we're not to the final answer yet. This study is just a piece of the puzzle."