Several recently published studies are fueling speculation — and concern — about whether chlorine disinfection byproducts are linked to respiratory illnesses, including asthma.

ASTHMA RISK In a recent study, researchers found a direct relationship between the number of hours teenage participants logged in outdoor pools and the prevalence of asthma.

The first, published in the journal Acta Pædiatrica,used data from the Norwegian Institute of Public Health’s Norwegian Mother and Child Study. It identified a possible connection between infant swimming and increased risk of breathing problems. The study included 30,000 participants, 25 percent of whom were enrolled in swim programs between birth and 6 months of age.

Forty-seven percent of infant swimmers experienced incidents of wheezing or tightness of the chest, between 6 and 18 months. These infants also were from mothers with asthma and allergies. By comparison, only 44 percent of nonswimmer infants from the same group experienced incidents of respiratory difficulties from ages 6 to 18 months.

The results show baby swimming may be related to later breathing problems, but further investigation is needed, said Wenche Nystad, department director of the NIPH’s Division of Epidemiology and a lead author of the study.

The second study looked at pools and the risks of asthma and allergies in adolescents. Published in the European Respiratory Journal, Dr. Alfred Bernard of Catholic University of Louvain, Brussels, Belgium, and his team examined 847 students with an average age of 15. They found that asthma risk increases consistently with the number of hours the teens spent in outdoor pools.

Findings indicate that those with the highest attendance at outdoor pools were approximately five times more likely to suffer from asthma than those who had never been in an outdoor pool. Bernard and his team noted that markers indicating a predisposition to respiratory problems also are a factor.