Association between sleep, sunlight exposure, and multimorbidity in older adults with and without mental illness

Background Light exposure and sleep are closely related to many chronic conditions. However, the associations between light exposure, sleep, and multimorbidity have been less well characterized, particularly in older adults with and without mental illness. Methods A cross-sectional study was conducted in two representative areas in Northwest China. Core sleep parameters, sleep-related symptoms, and sunlight exposure were collected using self-reported questionnaires. We clustered overall multimorbidity into three categories: physical-only, mental-only, and mental-physical multimorbidity. Separate multivariable binary logistic regression analyses were performed to examine the associations between sleep, sunlight exposure, and multimorbidity. Results Of the 1,018 participants, the mean age was 68.56 years, and 48.53% were female. Approximately half of the participants had two or more chronic conditions, including physical-only (21.22%), mental-only (1.57%), and mental-physical (28.49%) multimorbidity. Adjusted odds ratios (AORs) for sunlight exposure were significantly lower in older adults with mental-physical multimorbidity compared with those without. Higher odds for poor sleep quality, insomnia, snoring, and daytime sleepiness were observed in older adults with either category of multimorbidity. Sleep duration, non-extreme sleep timing, and sleep efficiency were associated with reduced odds for overall and mental-physical multimorbidity. Stratified analyses demonstrated stronger associations between sleep with multimorbidity in females and the younger-old group, whereas sunlight exposure was inversely associated with multimorbidity only in males. Conclusion Multimorbidity was prevalent in community-dwelling older adults. Adequate sunlight exposure and good sleep quality are associated with reduced odds of mental-physical multimorbidity.