Subject participation. The investigators will enroll a total 300 consecutive OSA male patients aged 20-60 yrs, with baseline apnea-hypopnea index ≥ 5 events per hour of sleep (AHI). In addition, 50 control subjects (AHI < 5) aged 20-60 yrs and matched by body mass index (BMI) are also to be recruited. Exclusion criteria will include any comorbid condition including alcohol and tobacco use.