Changes in weight and seasonal allergies can affect sleep apnea, and researchers writing in the journal Chest wanted to see if weather changes might also have an impact.

"More sleep disordered breathing events were recorded in wintertime than in other seasons," wrote study leader Cristiane Maria Cassol from the Universidade Federal do Rio Grande do Sul.

Cassol and her team said it could be due to several causes, including winter-related upper-airway problems that intensify the severity of symptoms and the use of burning wood to heat homes during the winter.

The team utilized data from sleep clinic patients and looked at how many times their rest was disturbed by breaks in breathing. The study included one night of sleep for more than 7,500 patients over a 10-year-period.

Researchers then compared the severity of the patients' apnea to the weather conditions at the time, including humidity, temperature and air pollution.

Patients who came in during colder months had more nighttime breaks in breathing than those who sought treatment during warmer months. During the winter, patients stopped breathing an average of 18 times an hour compared to 15 times an hour during the summer.

Similarly, the sleep clinic was more likely to see the most severe cases - people who stopped breathing more than 30 times an hour - during the colder months.

About 34 percent of patients who came in during cold weather had severe apnea, compared to 28 percent of patients during warmer weather.

The team found that certain weather conditions, such as high atmospheric pressure and humidity and high levels of the air pollutant carbon monoxide - were tied to worse cases of apnea.

But the study could not determine whether it was the weather itself that was responsible for the more severe apneas.

Jerome Dempsey, who studies breathing problems at the University of Wisconsin and wasn't involved in the study, said it makes sense that airway infections and weather could have an effect on sleep apnea, but that the changes across the seasons were small.

"There are so many things that affect sleep apnea, including the decision of when to come visit" a sleep clinic, Dempsey told Reuters Health.

In other words, it might not be the weather but the time of year that makes it more convenient for patients to take the time to seek treatment.

He added that while winter-related conditions such as colds or allergies might intensify sleep apnea, the biggest risk factor is obesity. SOURCE: bit.ly/MqNmmE

(Reporting from New York by Kerry Grens at Reuters Health; editing by Elaine Lies and Bob Tourtellotte)

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