Chronic sleep debt, according to a report from the University of Chicago, published in the Lancet for October 23, is becoming increasingly common, affecting millions of people in the more developed countries. It results from the habit of voluntarily restricting the hours spent in sleep every day because of other fancied claims upon time.
The idea current in 1910 that it was desirable to enjoy nine hours of sleep out of the 24 has now been cut to one of seven-and-a-half hours, in order to accommodate more time for work and leisure activities. Many shift workers, it is estimated, sleep on average less than five hours per working day.
The idea has gained currency that a "normal" sleep lasting eight hours nightly includes four to five hours of core sleep, mostly rapid eye movement (REM) sleep plus a residue of optional sleep, and that this component may be progressively decreased without incurring daytime drowsiness, mood changes or a decline in cognitive function. Nevertheless, evidence exists that a person's health may be adversely affected if this assumption is acted upon.
Investigations were made of the metabolic and hormonal variables in individuals whose daily period of sleep had been restricted or extended. Sleep curtailment over one week produced in healthy young people striking alterations both in metabolic and endocrine functions. Decreased carbohydrate tolerance and increased sympathetic tone were pinpointed as risk factors for insulin resistance, obesity and hypertension. Cortisol concentrations were raised in the evenings, reflecting impaired negative-feedback control of the hypothalamus-pituitary-adrenal system. The logical implication was the risk of insulin resistance and memory impairment increasing with the advance of ageing.
Thus, the metabolic and endocrine changes observed during periods of sleep debt reflect some of the adverse effects of the normal ageing process. Chronic sleep loss might increase the severity of the pathologies associated with ageing, such as diabetes and hypertension. The pursuit of more time for working and playing at the expense of sound sleep must be regarded as a threat to health.