FRIDAY, Feb. 3 (HealthDay News) -- Breast-feeding is associated with improved lung function in school-age children, particularly those with asthmatic mothers, a new study says.

Swiss and U.K. researchers analyzed data from nearly 1,500 U.K. children who were born between 1993 and 1997. Questionnaires were used to assess the duration of breast-feeding, other exposures, and respiratory symptoms.

The children's lung function was measured when they were 12 years old.

Breast-fed kids overall had a "modest improvement" in forced mid-expiratory flow (FEF50), which measures the amount and speed of air that comes out of the lung during the middle portion of a forced exhale.

But breast-fed kids whose mothers also had asthma also did better on two other lung function tests, forced vital capacity (FVC) and forced expiratory volume at 1 second (FEV1), according to Dr. Claudia Kuehni, a professor at the Institute of Social and Preventive Medicine at the University of Bern in Switzerland.

"In contrast, some earlier studies have suggested that breastfeeding might be harmful in the offspring of mothers with asthma," she noted in a journal news release.

The study appears online ahead of print in the American Journal of Respiratory and Critical Care Medicine.

More information

The U.S. National Institute of Child Health and Human Development has more about breastfeeding.