Sunday Nov 23, 2008 (foodconsumer.org) -- Recent studies have yielded strong evidence suggesting that high levels of vitamin D in women in pregnancy and during breastfeeding may protect against asthma in their children.

One study led by Dr. Tina Hartert, director of the Center for Asthma Research and Environmental Health at Vanderbilt University School of Medicine in Nashville, Tenn. suggests that infections in winter virus seasons may be a risk factor for asthma.

The study in the first December issue of the American Journal of Respiratory and Critical Care Medicine found babies born in the fall or autumn, 4 months before the peak of winter virus season, were 30 percent more likely to acquire asthma.

Hartert and associates speculate that winter viruses like respiratory syncytial virus or RSV may be responsible for the elevated risk of asthma and suggest that preventing these viruses could prevent asthma.

The notion that viral infections may increase risk of asthma is nothing new.

A study led by Jackson DJ and colleagues from the University of Wisconsin-Madison and published in the Oct 2008 issue of American Journal of Respiratory and Critical Care Medicine has already shown that RSV was strongly associated with asthma symptoms like wheezing.

Kackson et al. found "from birth to age 3 years, wheezing with respiratory syncytial virus (RSV) (odds ratio [OR], 2.6), rhinovirus (RV) (OR, 9.8), or both RV and RSV (OR , 10) was associated with increased asthma risk at age 6 years.

The results from the studies suggest that prevention of viral infections may help reduce risk of childhood asthma.  But they also suggest there may be another possibility. Deficiency of vitamin D may be a risk factor for asthma as well. That is, insufficient vitamin D can reduce immunity against viral infections and increase risk of asthma.

This possibility is far fetching.   A study led by Camargo C. A. JR and colleagues from Massachusetts General Hospital, Harvard Medical School in Boston, Mass. conclude that in the northeastern United States, a higher maternal intake of vitamin D during pregnancy may decrease the risk of recurrent wheeze in early childhood."

Camargo's study published in the March 2007 issue of American Journal of Clinical Nutrition was meant to examine the effect of vitamin D, which is known to have important immunologic effects, on asthma.

For the study, Camargo et al. followed up 1194 mother-child pairs for three years for incidence of recurrent wheeze in children.    Asthmatic children often suffer recurrent wheeze.   They also estimated the maternal intake of vitamin D during pregnancy from a validated food-frequency questionnaire.

They found women in the highest quartile (724 IU per day) had a 61 percent lower risk of having a child with recurrent wheeze.

Specifically, a 100-IU increase in vitamin D intake was linked with 19 percent lower risk regardless of whether vitamin D was from the diet or supplements.   The association was significant even after other factors were considered.

It is well known that in the winter, people are less likely to be outdoors. The results of that is the increased risk of vitamin D deficiency, which in turn increases risk of winter virus infections, a possible risk factor for asthma.

Vitamin D has been linked to immune system and lung development in uterus, according to Litonjua AA and Weiss ST from Brigham and Women's Hospital in Boston, MA. This could mean that insufficient maternal vitamin D may put fetuses at risk of asthma in their childhood.

Litonjua and Weiss said in their report published in the Nov 2007 issue of Allergy Clin Immunol that their epidemiologic studies had shown higher vitamin D intake by pregnant mothers reduces asthma risk by up to 40 percent in children 3 to 5 years old.

Hartert was cited as saying that parents should practice good hygiene and take infection-control measures such as washing their hands frequently to prevent winter virus infections and the development of asthma in their babies.

But because of the significance of vitamin D status, a health observer affiliated with foodconsumer.org suggested that supplements may be taken during pregnancy and breastfeeding. Or eat some oily fish if getting outdoors often for sunshine is not an option.