Girls who aren't milk-drinkers may have asthma risk

NEW YORK (Reuters Health) - Young girls who drink milk infrequently may have a higher risk of asthma than their peers, particularly if they are overweight, a new study suggests.

In a study of more than 700 girls and boys between 8 and 10 years old, Canadian researchers found a link between infrequent milk consumption - they defined as twice a week or less often -- and asthma risk, but only among girls.

Compared with their peers, girls with asthma were more than twice as likely to drink milk infrequently, the researchers report in the journal Allergy.

Some past studies have suggested that children who drink little or no milk are more likely than their peers to be overweight, and excess weight has also been linked to a higher asthma risk in children.

However, the current study found that low milk levels and excess weight were each by themselves linked to a higher asthma risk in girls. What's more, the combination of the two seemed especially problematic.

Asthmatic girls were nearly four times more likely than other girls to be overweight and to drink milk infrequently, the study found. This association was still seen after a range of other possible contributing factors were considered, including the children's overall diet, exercise habits and family income.

All of this suggests that low milk consumption may directly affect asthma risk, and in a manner unrelated to weight, according to the researchers, led by Dr. Anita L. Kozyrskyj, at the University of Manitoba in Winnipeg.

What that manner might be is not clear, but the researchers speculate on some possibilities.

Children who get little milk may be low in vitamin D, especially if they live in colder climates with limited sun exposure. Vitamin D, the researchers explain, seems to affect the way body's cells respond to the hormone estrogen. Some research suggests that estrogen is involved in airway inflammation, and that estrogen influences asthma symptoms in women.

Such an effect could potentially be exaggerated in overweight girls, according to Kozyrskyj and her colleagues, because their estrogen levels are typically higher than those of normal-weight girls.

For now, however, that remains speculation. More studies, the researchers conclude, are needed to weed out the relationship among milk consumption, weight and children's asthma risk.

SOURCE: Allergy, November 2007.