Vitamin D deficiency, which can occur even in "sun-replete" areas of the world, may lead to more severe asthma and allergies in childhood, researchers warn.

Dr. Juan C. Celedon at Boston's Brigham and Women's Hospital and co-investigators examined the association between vitamin D levels and markers of asthma severity and allergy in 616 asthmatic children from Costa Rica.

Twenty-one children, or 3.4 percent, had blood levels of the vitamin D metabolite 25-hydroxyvitamin D considered to be "deficient" and an additional 152, or 24.6 percent, had vitamin D levels considered "insufficient."

The investigators found that lower levels of vitamin D were associated with increased odds of being hospitalized for asthma, increased airway "twitchiness," and more severe allergies.

Celedon and colleagues report their findings in the American Journal of Respiratory and Critical Care Medicine for May 1.

In a linked editorial, Dr. Graham Devereux at the University of Aberdeen, UK and colleagues explain that even in nations close to the equator, the increasing tendency to avoid sunlight by staying indoors and wearing sunblock and more clothing when outside likely account for the high prevalence of inadequate vitamin D levels.

Still unknown, Devereux and colleagues note, is the role of vitamin D in the development of asthma, and whether vitamin D supplementation would be beneficial in the prevention or treatment of asthma.

"Ultimately," they say, "it is only by investigating the effects of vitamin D in doses at, and above those currently recommended, that decisions can be made on the optimal intake of vitamin D for health and the possible prevention and treatment of asthma."