You may not consider losing an hour or two of sleep a week a biggie. Score one for you—but only if you address your sleep debt with the same kind of focused effort you extend in paying your other bills.
That’s because regularly missing the recommended seven to nine hours of quality shut-eye will saddle you with what is known as sleep debt or sleep deficit. Simply put, it’s the cumulative impact of sleep loss on your body and mind.
As with credit card debt, the more you add to the balance, the deeper in the hole you go. Only with sleep debt, no collection agency will blow up your phone hounding you to pay up.
But the fuzzy-headedness, irritability, and fatigue that come along with sleep deprivation are mild compared to the more serious potential medical consequences of chronic sleep debt.
How sleep debt affects you
In the United States alone, insufficient sleep costs an estimated $411 billion a year in health care expenses and lost productivity, according to the RAND Corporation report “Why Sleep Matters: Quantifying the Economic Costs of Insufficient Sleep.”
Here are some specific examples of the consequences of sleep debt:
Sleep debt increases your risk of car accidents. The National Highway Traffic Safety Administration estimates that drowsy driving was responsible for 90,000 crashes, 33,000 injuries, and 736 deaths in 2015. The Centers for Disease Control and Prevention (CDC) says these numbers are underestimated, and up to 6,000 fatal crashes each year may be caused by drowsy drivers. Driving after staying up for 24 hours straight is like driving with a blood-alcohol level that would render you legally drunk in all 50 states.
Sleep debt raises your blood pressure. Student volunteers in a seminal University of Chicago study who slept only four hours a night for six consecutive days developed higher blood pressure, higher levels of cortisol (the stress hormone), and only half the usual number of antibodies in response to a flu vaccine. Not only that, but the volunteers also showed signs of insulin resistance, a precursor of metabolic syndrome and type 2 diabetes.
Sleep debt worsens your memory. Sleep debt doesn’t only affect your body, as demonstrated in a University of Pennsylvania and Harvard Medical School study of 48 healthy men and women, ages 21 to 38.
Before the study, the volunteers averaged seven to eight hours of sleep a night. Three-quarters of them were randomly assigned to three different groups that slept eight, six, or four hours per night. A fourth group agreed to go without sleep for three days. All of the participants completed sleepiness evaluation questionnaires every two hours during their waking period and took tests of reaction time, memory, and cognitive ability.
Over the two-week study period, the eight-hour group’s reaction times stayed about the same. In fact, their memory and cognitive scores rose. Meanwhile, the four-hour sleepers were more like the sleepless group, whose scores nosedived during their three days without sleep. After two weeks, the four-hour group’s memory scores and reaction times were about the same as the sleepless group after its first sleepless night.
The six-hour sleepers did OK on the cognitive test but slipped on reaction time and memory, with scores like those of the sleepless group after their first night awake.
Related: A simple way to protect yourself against Alzheimer’s disease
How to catch up on sleep and pay back your sleep debt
As with eliminating other types of debts, the best strategy is to make a plan to pay it back a bit at a time—and commit to sticking with it. Start low and go slow. Simply turning in 15 minutes earlier than usual can help you catch up, as will sticking to a regular sleep-wake routine.
Here are a few other suggestions for getting out of sleep debt:
- For short-term sleep debt—if you missed, say, 10 hours of sleep during the week: Add three to four extra hours on the weekend and an extra hour or two the next week until your sleep debt is paid in full. A 2018 study published in the Journal of Sleep Research found that sleeping more on the weekend could compensate for less sleep during the week.
- For long-term sleep debt—if you’ve shortchanged yourself in the sleep department for decades: It could take weeks to reset your body and settle your sleep debt. The ideal situation: Plan a vacation with few demands on your time. Don’t set the alarm and sleep until you naturally wake up. You may feel like a hibernating bear at first, sleeping for 12 hours or longer. But gradually your body will adjust and you will naturally wake up feeling refreshed once your body has been reset to this new normal.
How to stay out of sleep debt for good
Once you determine how much sleep you need to feel your best, block it out in your daily schedule. Prioritize it. You don’t want to backslide into a deficit all over again. Harvard Medical School’s Women’s Health Watch newsletter offers these practical steps to keep your sleep ledger balanced. (And yes, it applies to you too, guys.)
Stay out of sleep debt by:
- Trying to go to bed and get up at the same time every day.
- Reserving your sleep space for sleep, sex, and restful activities such as pleasure reading or meditation.
- Napping in the afternoon but only if necessary, as it can interfere with your sleep schedule.
- Avoiding caffeine in the afternoon and evening and going easy on the hooch.
- Exercising regularly—but not within three hours of bedtime.
Make sure you speak with your doctor if you believe you’re getting enough sleep yet don’t feel refreshed in the morning. It could be due to any number of common conditions, from depression to sleep apnea.
For help winding down at night and preventing yourself from going into sleep debt, here are 10 nighttime activities that’ll relax you before bed.
