Objective memory performance can be associated with reported sleep duration, with 7 hours representing a universal optimum for cognition in adults.
Sleep duration varies substantially within each individual and between individuals. Understanding the determinants of these variations is key in many health and social fields since sleep is essential for our well-being. Sleep has a profound effect on our bodily functions, from the functioning of genes and cells through various physiological processes, from immunity and metabolism to complex brain functions related to cognition and mental health. Both genetic (for example, gender) and environmental (for example, artificial lighting) factors modulate sleep. In particular, age has been shown to explain a large part of the variance in sleep duration within the general population, since children sleep considerably more and better than adults, and younger adults sleep less than older ones. Reported sleep duration has been found to vary from country to country, with Asians (eg Japan, Indonesia, Malaysia, and the Philippines) getting less sleep on average than others.
Researchers from UCL, the University of East Anglia, and the University of Lyon have determined that sleep duration decreases in early adulthood up to age 33, and increases again at age 53. The study, in which they participated 730,187 people from 63 countries, revealed how sleep patterns change throughout life and how they differ from country to country
Scientists led by Professor Hugo Spiers (UCL Psychology and Language Sciences) and Dr. Antoine Coutrot (CNRS, University of Lyon) found that, across the sample, people sleep an average of 7.01 hours per night, and that women sleep 7.5 minutes more on average than men.
The youngest participants (minimum age 19 years) slept the most, with sleep duration decreasing in their 20s and 30s, before leveling off in their 50s and increasing again. The pattern, including the newly identified milestones of age 33, when sleep decline stabilizes, and age 53, when sleep increases again, was the same for men and women and across countries and levels of education.
The researchers say the decline in sleep during midlife may be due to the demands of childcare and work life.
People who report sleeping more are those from Eastern European countries such as Albania, Slovakia, Romania, and the Czech Republic, who report sleeping between 20 and 40 minutes more per night, and those who report less, are those from Southeast Asian countries such as the Philippines, Malaysia, and Indonesia. UK residents reported sleeping slightly less than average. In countries closer to the equator, people tended to get a little less sleep.
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