Interferon-gamma moderation of poor sleep maintenance and depressed mood in community-dwelling older adults

Background. Depressive symptoms, such as depressed mood, are common in older adults and associated with an increased risk for morbidity and mortality. Given the evidence that sleep disturbance and alterations in interferon (IFN)-gamma biology are associated with depression risk, this study examines the separate and joint contributions of poor sleep maintenance and IFN-gamma to depressed mood in older adults. Methods. Community-dwelling, non-depressed older adults (n = 36, 72.1 +/- 6.8 years) underwent a night of polysomnography to assess sleep maintenance [i.e. wake time after sleep onset (WASO)]. The morning after polysomnography, plasma levels of IFN-gamma were evaluated along with self-reported depressed mood throughout the day. Multivariate linear regression tested associations of WASO and IFN-gamma with the severity of depressed mood. In addition, moderation and mediation models examined the role of IFN-gamma for the relationship between WASO and depressed mood. Results. A greater amount of WASO (p < 0.05) and higher levels of IFN-gamma (p < 0.01) were both associated with the severity of depressed mood. Moreover, IFN-gamma moderated the relationship between WASO and depressed mood (p < 0.01), such that WASO was more strongly related to the depressed mood among those with higher IFN-y, than among those with lower IFN-gamma. However, IFN-gamma did not mediate the relationship between WASO and depressed mood. Conclusion. In this study of older adults, poor sleep maintenance and higher levels of IFN-gamma were both related to depressed mood. Moreover, IFN-gamma moderated the relationship between poor sleep maintenance and depressed mood. Together, these findings suggest that older adults with higher IFN-gamma are at heightened risk for depressive symptoms following sleep disturbance.