Forty-four hours, or eleven nights of less than seven hours of sleep: this is what every human being is currently losing in sleep time due to rising temperatures, according to a study conducted by Danish researchers from the university of Copenhagen between the years 2015 and 2017 and published in the journal One Earth May 20, 2022.
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To carry out its work, the Danish team collected data provided by a sample of 47,000 people from 68 countries, equipped with a sleep monitoring bracelet, which they cross-referenced with local meteorological data. That is, in all, some seven million nights of sleep recorded. At the end of their work, they were able to establish that from 25°VS measured outdoors, the probability of not enjoying restful sleep is multiplied by 3.5. Indeed, while the ideal temperature for falling asleep is around 19°C, higher outside temperatures delay the moment of falling asleep (since we need our body to cool down for us to fall asleep) and advance the hour of our awakening.
This deterioration in sleep time could increase in the future: scientists from the University of Copenhagen have established that the rise in temperatures caused by global warming could deprive us of 50 to 58 hours of sleep per year by 2099.
Among the first affected, women and the elderly: under identical conditions, the core body temperature of women decreases earlier in the evening than that of men, explains the study, which could expose women to environmental temperatures too high when they usually begin to sleep. The body of older people regulates heat less effectively than younger people.
The researchers argue, acknowledging however that they cannot prove it, that the inhabitants of developing countries could be more concerned, since they are less equipped with an air conditioning system.
With, in addition, serious consequences on mental health, a reduction in cognitive performance, a drop in productivity, an increase in absenteeism, a drop in the efficiency of the immune system, a high risk of hypertension. And more depression and suicidal behavior.
Sleep deprivation also delays reaction times, increases the risk of accidents, inhibits the neuronal encoding of new experiences in memory and limits the elimination of neurotoxic metabolites from the brain linked to aging and neurodegenerative diseases. Finally, lack of sleep would greatly increase the feeling of hunger: in another study published in March 2017, scientists from the University of Pennsylvania established that nights of less than six hours favored the production of ghrelin, the digestive hormone that stimulates appetite, and decreases that of leptin, which regulates fat stores in the body and appetite by controlling the feeling of satiety.
The publication of this study comes at a time when the heat wave which is raging in India and Pakistan has already caused the death of 90 people. According to scientists from the World Weather Attribution (WWA), the network of pioneering scientists in the attribution of extreme events to climate change, this heatwave episode was made thirty times more likely by climate change.