Background: It is postulated that obstructive sleep apnea (OSA) is a risk factor for the development of depression. However, obesity and excessive daytime sleepiness (EDS) are associated with both OSA and depression. The goal of this study was to examine the relative contribution of OSA, obesity and EDS to incident depression.
Methods: A representative random sample of 1137 adults without depression from the Penn State Adult Cohort was followed up after 7.5 years. All subjects underwent a full medical examination and polysomnography at baseline. OSA was defined as an apnea/hypopnea index (AHI) ⩾5, overweight as a body mass index (BMI) of 25-29.9 kg m(-)(2), obesity as a BMI⩾30 kg m(-)(2) and EDS as moderate-to-severe drowsiness/sleepiness and/or irresistible sleep attacks.
Results: Overweight, obesity and EDS were associated with incident depression, whereas OSA alone was not. Overweight was associated with incident depression in women, while obesity and EDS were associated with incident depression in both genders. The association of overweight and obesity with incident depression was independent of premorbid emotional distress, while that of EDS was not. The association between BMI and EDS with incident depression was stronger in women 20-40 years old. The severity of EDS predicted incident depression in those with OSA, while AHI or oxygen desaturation did not.
Conclusions: Overweight, obesity and EDS are the main predictors of incident depression. Obesity may be linked to depression through psychobiological mechanisms, while EDS may be an early sign of depression. Obesity should be a target of our preventative strategies for depression.