Changes in sleep quality with age–a 36-year follow-up study of Finnish working-aged adults
Long-term follow-up data on changes in sleep quality among middle-aged adults is scarce. We assessed sleep quality in a population-based cohort (n = 4847) of twins born between 1945 and 1957 during a follow-up of 36 years, with four measurement points in 1975, 1981, 1990 and 2011. Sleep quality was categorized as sleeping well, fairly well, fairly poorly or poorly. The mean age at the beginning of follow-up was 24.0, and at the end was 60.3 years. Of all the adults, 71.1% slept well or fairly well at each time-point throughout the follow-up and 0.5% poorly or fairly poorly. The proportion of those sleeping poorly or fairly poorly increased linearly over time; 3.5% among both sexes at the start, and 15.5% among men and 20.9% among women at the end of the follow-up. The last survey indicated a strong association between self-rated health and sleep quality: sleeping poorly or fairly poorly was reported 15 times more frequently by those rating their health as fairly poor than by those rating their health as very good. There was a strong association between indicators of depression and poor sleep. Although many studies have reported increasing frequencies in sleep problems, our results, based on a long-term cohort study, indicate that the majority of people sleep well or fairly well. Sleep quality declines with age, but only a very small fraction of the adults in this long follow-up consistently slept poorly.