Dr. Avnish Jolly, Chandigarh :The participants were then randomised to staying in the sleep lab for another three 24-hour days, four 24-hour days, or seven 24-hour days. On these days, they had 16 hours of “sleep opportunity”, 12 during the night and four during the day.
The participant’s preference for mornings or evenings was measured using the Owl-Lark score. The physiological characteristics of sleep were measured using polysomnography, a technique where electrodes and movement-tracking devices are attached to the subject while asleep. This recorded the times and durations that the participants entered rapid-eye-movement (REM) sleep and non-REM sleep. The researchers also asked about the subjective experiences of sleep and waking performance and compared the responses of the younger and the older recruits.
The total time that people sleep when freely allowed to do so reduces in a curve over time, and so the researchers used statistical models to estimate the eventual duration of sleep that the volunteers would be expected to reach if allowed to do so beyond the end of the experiment. This is known as the asymptotic duration of sleep.
At the beginning of their time in the sleep lab, older subjects had less daytime sleep propensity (the ability to fall asleep during the day as measured on the MSLT) than younger subjects.Total daily sleep duration in the sleep lab was initially longer than the habitual sleep duration recorded at home, and then declined during the experiment. The predicted asymptotic values were 1.5 hours shorter in older subjects (7.4 hours) than in younger subjects (8.9 hours). REM sleep and non-REM sleep contributed about equally to this reduction.
The researchers concluded that in the absence of social and usual daily constraints, both the ability to fall asleep during the day and the maximal capacity for sleep are reduced in older people. They suggest that this has important implications for understanding age-related insomnia. These findings of this study contribute to a debate regarding the amount of sleep required for maintaining alertness, performance and good health. The researchers are cautious in their interpretation of the results, saying that there are various conceptual models of sleep that highlight the contribution of daily physiological cycles, as well as some that explain the social and lifestyle factors that determine sleep duration.
The questioner of this study does not allow the researchers to explain causation, why older people sleep less. Whether older people have a decreased ability or need to sleep is not resolved by the data. However, the 1.5 hours reduction in the predicted sleep duration for older subjects does suggest that when allowed to sleep as much as they want to, older people sleep less overall. These observations may be helpful in that they suggest theories that can be tested in further research. It is known that sleep requirements vary between individuals, and there is an acknowledged decline with age that can safely be interpreted as a reduced “need”.