Didikoglu A, et al. - Using the University of Manchester Longitudinal Study of Cognition in Normal Healthy Old Age cohort (n = 6,375; age 42 to 94 years), researchers studied sleep efficiency determinants, heterogeneity in the trajectory of an individual's sleep efficiency over a period of up to 27 years in later life, and its relationship with health. Using self-report validated instruments (Cornell Medical Index, Beck Depression Inventory and Geriatric Depression Scale), depression and health data were gathered. Three trajectory clusters for sleep efficiency were recognized: high (32%), medium (50%) and low sleep efficiency (18%). Low prevalence of hypertension, circulatory problems, general arthritis, breathing problems, and recurrent episodes of depression were associated with the high sleep efficiency cluster. Overall, sleep efficiency is reduced by aging, and different diseases are related to different, detectable sleep efficiency subgroups.