TORONTO, ON — Sleep clinics see the most severe cases of sleep apnea during the winter, but researchers can’t determine if the weather itself is responsible for the severity of sleep apnea.

A new study from Brazil shows that respiration problems associated with obtrusive sleep apnea tend to worsen during the cold winter months. Researchers found that changes in weight, climate and seasonal allergies can all affect sleep apnea.

"More sleep disordered breathing events were recorded in wintertime than in other seasons," the study noted.

The study says that the severity of symptoms could be the result of winter-related upper- airway problems, but other causes may also contribute.

The research team in Brazil used data from 7,500 sleep clinic patients over a 10 year period, according to Reuters. The team looked at how many times patients’ rest was disturbed by breaks in breathing, then compared the severity of the apnea to the weather conditions at the time. The researchers looked at humidity, temperature and air pollution.

Researchers concluded that patients who came to be treated for sleep apnea during colder months had more nighttime breaks in breathing than those who came during the warmer months, but could not definitely determine whether the weather was responsible for more severe cases of sleep apnea.