The true cost of sleep debt

Put down the remote. Turn out the lights. You’re already likely deep in debt. As the war on sleep intensifies — driven by factors such as rising stress levels, poor diets, pollution (particularly air and light), screens, streaming and the commodification of attention — the world is seeing a rising incidence of sleep debt.

Typically, a shortfall of 25% or more is considered sleep debt. For a person who needs seven hours of sleep a day, five hours of sleep would be the start of such a cycle.

A key misunderstanding driving levels of sleep debt up is the idea that if one sleeps significantly less on some nights and more on others, the scales will eventually even out. Doctors say this is an unhealthy and ultimately unsustainable way of viewing sleep, primarily because the window within which one must erase sleep debt is so small.

One should ideally make up for lost sleep the same day, with a nap or two. A six-week study by researchers from the University of Pennsylvania, Virginia Polytechnic Institute and State University, and the NASA Johnson Space Center, published in the journal Sleep in August 2021, found that recovery sleep over the weekend, for instance, did not help restore vital functions such as vigilant attention that were impaired after five days of sleep deprivation (with sleep for these subjects restricted to five hours a night).

“Studies show that over 30% of the American population has a sleep debt problem; in India while sleep debt is prevalent, we do not have adequate research pointing towards how widespread the issue is,” says Bindu Kutty, professor of neurophysiology and head of the Centre for Consciousness Studies, National Institute of Mental Health and Neurosciences (NIMHANS), Bengaluru.

Over time, sleep debt can cause fatigue, irritability, reduced attention spans and drowsiness affecting cognitive and other functions. But what it also does is contribute to the ageing of the body. This means that, in a sense, one is literally losing time.

“We are horrible at recognising sleep debt unless it is acute,” says Dr Seema Khosla, a pulmonologist, sleep medicine specialist and medical director of the North Dakota Center for Sleep. She adds that a frequent six-hour sleeper won’t notice how they get a little more sluggish as the week progresses. “A good litmus test is to wake up spontaneously, without relying on an alarm clock. If you feel refreshed, you are getting enough sleep,” she says.

It helps, adds Dr Khosla, to change how one views sleep. “As a colleague put it, think of it as the start of the next day,” she says, “instead of the end of your current one”.