An urban nightmare

you have to lose something to gain something. This phrase is well-suited especially for the sleepless nights exchanged for parties, shopping, family visits and extra hours of work to make up for off-days. In fact, sleep deprivation has become almost normal among residents in urban areas, with people getting used to being tired and thinking, optimistically, that they will catch up with their lost sleep tomorrow. And that tomorrow never comes.

But few know that lost sleep can spell trouble. New research suggests that the consequences of chronic sleep deprivation may be far worse than simply diminished mental sharpness, shortened tempers and a tendency to doze off at every quiet moment. Sleep scientists have found that those who suffer from an "accumulated sleep debt' may develop serious problems, including obesity, diabetes and high blood pressure.

Sleep experts consider "normal' night sleep about eight hours comprising four-five hours of core sleep, that includes most of the non-rapid movement (non- rem ) sleep, and the rest optional (slow wave) sleep. There have been some suggestions that the optimal sleep can be done away with partially without significant daytime sleepiness, mood changes and detectable decline in cognitive function.

Despite 50 years of research, we still do not seem to know enough about sleep. Top on the list of questions is: "Why do we sleep?' Most studies on sleep also appear to have focussed on the brain and related functions. Interestingly, even the multitude of sleep researchers, who have looked at metabolic and endocrine functions and cardiovascular events, appear to have thought that sleep is for the brain alone and not for the rest of the body and that sleep debt has little no effect on the overall functions of the body.

However, Eve Van Cauter and her team from the University of Chicago, Illinois, have come up with findings that prove that sleep debt does have harmful impacts on the carbohydrate and endocrine functions ( The Lancet , Vol 354, No 9188).

Cauter and her team assessed the metabolic functions in 11 young men for 16 consecutive days. In the first three days, they slept for eight hours. Their sleep was restricted to four hours per night for the next six days. The following seven days, they were allowed the luxury of staying in bed for 12 hours.

The researchers found that glucose and insulin responses were severely affected in sleep-deprived young men. In fact, the researchers found insulin response in them to be similar to non-insulin-dependent diabetes patients. This decreased carbohydrate tolerance and the heart rate variability too