Actigraphy-based Assessment of Sleep Parameters in an Ageing Rural South African Population

Background: The relationship between sleep and ageing is well established, with parameters such as sleep efficiency and total sleep time declining with age. Current understanding of sleep health and the determination of normal sleep characteristics is largely derived from data collected in urban first-world populations. Here, we aim to establish whether this relationship is also observed in an ageing rural population of Africans living in Africa.

Methods:Participants (N = 205; aged 68.8 ± 12.01; 112 females) of a cohort study conducted in Agincourt, South Africa, were selected for this study. Participants wore an accelerometer on their non-dominant wrist for a minimum of 5 nights of actigraphy (ActTrust, Condor Instruments, São Paulo Brazil). Measures of 24-h activity rhythms, sleep duration and timing, light exposure, and peripheral body temperature was collected using actigraphy. 

Results : Non-parametric analysis of the data derived parameters associated with activity levels across the day and the night.  Linear regressions were performed to determine the relationship between age and a number of sleep characteristics, controlled for sex. The analyses revealed a significant positive relationship between age, total sleep time (F(2,194) = 6.827; p=0.001) and sleep efficiency (F(2,194) = 5.62; p=0.004). The analyses showed no significant relationship between mid-sleep point and age.

Conclusions: In this cross-sectional study, total sleep time and sleep efficiency demonstrated a positive association with age, in addition to the timing of sleep remaining stable as age increased. This contradicts our current understanding of sleep and ageing. Possible reasons include survivor effects, however, it is worth noting that this population differs from those studied in the majority of the published literature both in their ancestry and in their rural location and consequent greater exposure to natural and lesser exposure to artificial light.