June 10 (HealthDay News) -- Though obesity is a known major risk factor for obstructive sleep apnea, many non-obese people also have the condition, according to the results of a new study.

Among 5,426 non-obese adults (with a body-mass index between 18.5 and 27), obstructive sleep apnea (OSA) was present in 54 percent. About half of those with the condition had mild cases and half had moderate to severe OSA.

The study found that moderate to severe OSA was most common in middle-age men with larger neck sizes.

The researchers noted that they were surprised to find no significant differences in Epworth Sleepiness Scale results and neck size between non-obese people who did and did not have OSA. The scale is a standardized method of measuring daytime sleepiness.

"More than 50 percent of non-obese OSA patients had mild OSA, suggesting that in-lab polysomnography may be more accurate in assessing people in this demographic, as opposed to portable monitoring systems," lead author Teimur Yeligulashvili, clinical supervisor at SleepTech in Wayne, N.J., said in a news release from the American Academy of Sleep Medicine.

The study was presented Tuesday in Seattle at the annual meeting of the Associated Professional Sleep Societies.

Earlier research had found an association between OSA and serious health problems such as heart disease, obesity, diabetes, hypertension and increased risk of death.

SOURCE: American Academy of Sleep Medicine, news release, June 9, 2009