Pregnant women who get ample amounts of vitamin D may be protecting their unborn children from developing asthma later in life, a U.S. study suggests.
Researchers at Massachusetts General Hospital in Boston used questionnaires to assess vitamin D levels of women when they were pregnant.
They then matched this data with the children who were showing early signs of asthma -- recurrent wheeze -- by the age of 3.
"The higher the maternal level of vitamin D, the lower the child's risk [of asthma]" said Carlos Camargo, lead researcher of the study published in the American Journal of Clinical Nutrition.
Vitamin D is obtained from some foods, including oily fish such as salmon. It is also produced in the skin as a result of exposure to sunlight.
But, during winter months, the sun's rays just aren't strong enough to trigger vitamin D production.
"I think adults in northern latitudes should take vitamin D supplements," Dr. Camargo said in an e-mail.
"The optimal dose is not yet clear, but a recommendation of 800 to 1,000 International Units a day is safe and is known to increase blood levels of vitamin D during these winter months."