Healthy sleep durations appear to vary across cultures

Past research finds that sleep duration is reliably linked with health yet sleep durations differ substantially between countries. We investigated whether countries with shorter sleep durations have worse health. Study 1 analyzed national sleep durations from 14 past investigations (<i>k</i> = 353) and found that they were not associated with national health. Study 2 collected sleep duration and health data from people from 20 different countries (<i>N</i> = 4,933). Average sleep durations varied substantially between countries (range = 1.57 h). A quadratic relation between sleep duration and health was found in all countries, although the turning points varied between countries. Individuals whose sleep duration was closer to their country's perceived ideal reported better health. The results suggest that the amount of sleep associated with optimal health varies across countries.