(REUTERS) — Fully half of the 400 women given overnight sleep tests in a new Swedish study turned out to have mild-to-severe sleep apnea.

In the random population sample of adult women who answered a questionnaire and were monitored while sleeping, half experienced at least five episodes an hour when they stopped breathing for longer than 10 seconds, the minimum definition of sleep apnea.

Among women with hypertension or who were obese – two risk factors for sleep apnea – the numbers were even higher, reaching 80 to 84 percent of women.

Many of the women in the study represent mild cases of sleep apnea.

“How important is the mild sleep apnea, we don’t know,” said Dr. Karl Franklin, the lead author of the study and a professor at Umea University in Sweden.

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