RESUMEN
Sleep behaviour has been extensively studied with questionnaires in industrialised countries to investigate the epidemiology of sleep-wake disorders. However, only few attempts have yet been made to examine sleep behaviour of people living in Africa. Although, a large number of studies in hot or cold environments have used short-term exposures, reporting disrupted sleep for most of them, long-term exposures to stressful thermal environments are rare in the literature. Prior to the present investigation, we used questionnaires to analyse the effects of seasonal heat increase on perceived sleep behaviour and sleep quality in young native African students in Niger [7], even though these methods of investigation are by no means as accurate as polysomnographic recordings. The hypothesis was that sleep behaviour may be influenced by climatic variations in a hot dry tropical climate. Such climatic variations have been shown to induce seasonal heat acclimatisation marked by changes in body temperature rhythms in the hot versus the cool season [13]. Sleep behaviour was examined during two 7-day periods in January ("cool-dry" season, 88 subjects) and May ("hot-dry" season, 53 subjects). The questionnaire was completed after night sleep and/or naps. The subjects slept an average of 7 1/2 hours a day, most of them having afternoon naps. They experienced no major seasonal variation in their sleep behaviour, but for an increased number of awakenings during the hot season. Restorative quality of sleep scored lower after a nap than after nocturnal sleep. Therefore, general sleep characteristics were not modified by seasonal temperature variations in African native students, perhaps because of the limited changes in daylight under the low latitude of Niamey. Another investigation was carried out using the same 12-item questionnaire in Abidjan on 78 medical students who did not have a nap [9]. Contrary to the Niamey students, the Abidjan subjects adopted short duration sleep schedules, without any effect on the subjective quality of the restorative properties of their sleep.