ASTHMA MAY LEAD TO SLEEP DISORDER

People who suffer from asthma are at an increased risk of developing sleep apnea, a disorder that causes breathing difficulties while sleeping, a new study has warned. Researchers at the University of Wisconsin used data from the Wisconsin Sleep Cohort Study, which has been following approximately 1,500 people since 1988. They found that patients who had asthma were 1.70 times more likely to develop sleep apnea after eight years. "This is the first longitudinal study to suggest a causal relationship between asthma and sleep apnea diagnosed in laboratory-based sleep studies," said Mihaela Teodorescu, assistant professor of medicine at the university. "Cross-sectional studies have shown that OSA is more common among those with asthma, but those studies weren't designed to address the direction of the relationship," Teodorescu said. The connection between asthma and obstructive sleep apnea (OSA) was even stronger among participants who developed asthma as children. Childhood-onset asthma was associated with 2.34 times the likelihood of developing sleep apnea. The researchers also found that the duration of asthma affected the chances of developing sleep apnea. For every five-year increase in asthma duration, the chances of developing OSA after eight years increased by 10 per cent. Participants in the Wisconsin Sleep Cohort, who were all between the ages of 30 and 60 in 1988, completed in-laboratory polysomnography, clinical assessments and health history questionnaires every four years. For the asthma-OSA study, the researchers focused on 773 cohort enrollees who did not have OSA when they joined the study and then determined whether their sleep apnea status had changed after eight years. During the eight-year follow-up period, 45 subjects developed asthma, and they were 48 per cent more likely to develop new-onset sleep apnea. However, because the sample size was small, the increase lacked statistical significance. "Forty-eight per cent represents a large difference," said Paul Peppard, an assistant professor of population health sciences at the university and a principal investigator of the Wisconsin Sleep Cohort Study. "This is one result that calls for a follow-up study. If confirmed by a larger study with more asthma cases, the finding would have important clinical relevance," Peppard said. "For now, it makes sense for clinicians to consider asthma history, as well as more traditional factors associated with OSA such as obesity, when deciding whether to evaluate patients for OSA with a sleep study," he said. The study will be presented at the American Thoracic Society 2013 International Conference in Philadelphia.