How humidity and CO2 affect the sleep of older adults? -Insights for improving sleep quality through environmental control

A laboratory measurement was carried out to investigate the effects and elucidate the mechanisms through which indoor relative humidity and carbon dioxide (CO2) concentration impact the sleep of older adults. The electroencephalogram, electrooculogram, chin electromyogram, electrocardiogram, respiration, oxygen saturation and wrist skin temperature of participants were measured continuously during sleep. Urine samples were collected and blood pressure was measured both before and after sleep. The results indicated that compared with a relative humidity of 60%, the sleep quality of older adults decreased at both 40% and 80%. Higher CO2 concentrations, particularly when combined with the low relative humidity, result in significant decrease in sleep quality, which consequently raised the risk of cardiovascular disease, oxidative stress, and inflammation. The results of physiological measurements indicated that the low/high relative humidity and high CO2 concentration disturbed sleep probably by affecting autonomic nervous activities, sleep-disordered breathing, thermoregulation, and systemic inflammation. This study suggests that good ventilation and the avoidance of low/high relative humidity in the bedroom are all important for the sleep quality and health of older adults, and that the lower limit of indoor relative humidity recommended by current standards or guidelines might not be optimal for maintaining sleep of older adults.