Snooze, don’t lose: The true cost of sleep debt

People think they can make up for lost sleep by just sleeping more “later on” but that’s a dangerous and unsustainable approach, doctors say. The window for erasing sleep debt is so small, one must ideally make up for it in the same day, with a nap or two.

Put down the remote. Turn out the lights. You’re already likely deep in debt.

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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 at least 25% 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, risky 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 more than 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 at the 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 and sleep medicine specialist, medical director of the North Dakota Center for Sleep, and a spokesperson for the American Academy of Sleep Medicine. She adds that a frequent six-hour sleeper won’t notice how they get a little more sluggish or crankier as the week progresses. “A good litmus test to check if you have accumulated sleep debt is to wake up spontaneously, without relying on an alarm clock. If you feel refreshed, you are getting enough sleep,” she says. Keeping a sleep diary and recording how one feels every morning can help as well.

It’s a good idea, adds Dr Khosla, to change how one view sleep. “Think of it as the beginning of the next day,” she says, “instead of the end of your current one”.