Influence of Day Length and Physical Activity on Sleep Patterns in Older Icelandic Men and Women

Study Objectives: To identify cross-sectional and seasonal patterns of sleep and physical activity (PA) in community-dwelling, older Icelandic adults using accelerometers. Methods: A seven-day free-living protocol of 244 (110 female) adults aged 79.7 +/- 4.9 years was conducted as part of a larger population-based longitudinal observational-cohort study in the greater Reykjavik area of Iceland. A subpopulation (n = 72) repeated the 7-day measurement during seasonal periods with greater (13.4 +/- 1.4 h) and lesser (7.7 +/- 1.8 h) daylight. Results: Cross-sectional analyses using multiple linear regression models revealed that day length was a significant independent predictor of sleep duration, mid-sleep, and rise time (all p <0.05). However, the actual within-individual differences in sleep patterns of the repeaters were rather subtle between periods of longer and shorter day-lengths. Compared to women, men had a shorter sleep duration (462 +/- 80 vs. 487 +/- 68 minutes, p = 0.008), earlier rise time, and a greater number of awakenings per night (46.5 +/- 18.3 vs. 40.2 +/- 15.7, p = 0.007), but sleep efficiency and onset latency were similar between the two sexes. Daily PA was also similar between men and women and between periods of longer and shorter day-lengths. BMI, age, gender, and overall PA all contributed to the variations in sleep parameters using multiple regression analysis. Conclusions: The sleep and PA characteristics of this unique population revealed some gender differences, but there was limited variation in response to significant daylight changes which may be due to long-term adaptation.