Sleep debt doesn't clear on a Saturday

Quick answer: Most healthy adults need at least seven hours a night. Teenagers need more, usually eight to ten. If you're running on six and calling it fine, you're probably the last person to notice the damage. Pay a debt back in small installments over several nights. One twelve-hour Saturday doesn't do it.

The ledger

Sleep debt is simple arithmetic. Say you need eight hours and get six on a weeknight. That's two hours owed. Do it five nights running and you're ten hours in the hole by Friday, the equivalent of skipping an entire night of sleep, spread thin enough that you never feel the drop.

That's the trap. Short sleep makes you worse at judging how short sleep is making you.

A well-known 2003 study in the journal Sleep kept volunteers on four, six or eight hours a night for two weeks. The six-hour group's reaction and attention scores slid day after day. By the end, they tested like people who'd gone without sleep entirely. Yet they rated themselves only a little sleepy. Their gauge was broken and they didn't know it.

If your spouse says you're short-tempered in the evenings, or the kids have learned to ask you things before nine at night, take that as data.

What you actually need

Public health guidance, including the CDC's, puts adults at seven or more hours. That's a floor, not a target. Plenty of people need seven and a half or eight, and some need nine.

Your number is a fact about you, not a matter of discipline. You can find it.

A two-week test:

• Pick a stretch with no early obligations. A vacation works. A slow stretch at work works too.
• Set a bedtime that gives you eight and a half hours in bed. Phone down, lights out.
• Skip the alarm.
• The first several days you'll sleep long. That's the debt coming due. Don't count those nights.
• After a week or so, your sleep settles into a pattern. Wake time stops drifting. That settled length is close to your real need.

Most men who run this test are surprised. They've been calling themselves "a five-hour guy" for twenty years and turn out to be a seven-and-a-half-hour guy with a bad habit.

What shorting yourself costs

The effects aren't dramatic one night at a time. That's why people ignore them.

• Your head. Focus, memory and patience go first. You reread the same email. You snap at somebody you love.
• Your appetite. Tired people want sugar and carbs, and they usually get them. Short sleep has been linked with blood sugar trouble, which is worth knowing if you've had a number like the one in Your A1C Came Back 5.9. Now What?
• Your heart. Chronic short sleep is associated with higher blood pressure and heart disease risk. If your blood pressure runs high, ask your doctor about your sleep along with your salt.
• Your mood. Poor sleep and anxiety or low mood feed each other. It's hard to tell which started it. Stress Doesn't Stay in Your Head covers how that loop reaches the rest of your body.
• Your driving. This is the one that kills people. A drowsy driver can slip into a microsleep for a few seconds. At highway speed, a few seconds is the length of a football field. If you're yawning, drifting in your lane or can't remember the last few miles, pull over. Don't bargain with it.

How to pay it back

Forget the heroic recovery. A steadier approach works better.

Go to bed earlier, not wake up later. Add thirty to sixty minutes to your sleep each night for a week or more. Moving bedtime keeps your wake time steady, and a steady wake time is the strongest anchor your body clock has.

Allow one longer morning, not two. An extra hour or so on the weekend is fine. Sleeping until noon on both days shoves your clock around and makes Sunday night miserable. Sleeping in can ease the sleepiness. It may not undo everything that a short week did, so don't treat Saturday as a license.

Nap short and early. Twenty to thirty minutes, before mid-afternoon. A long nap at 5 p.m. just steals from tonight.

Cut caffeine earlier than you think. Caffeine hangs around in your body for hours. If you drink coffee at 3 p.m. and lie awake at midnight, you have your answer. Aim to be done by early afternoon.

Be honest about alcohol. A couple of drinks may make you drowsy, but they chop up the second half of the night. You wake at 3 a.m. and can't get back down.

Make the room work. Cool, dark, quiet. Blackout curtains run about thirty dollars. A fan covers a noisy street. The phone charges across the room, not on the nightstand.

When it isn't a habit problem

Sometimes you do everything right and still wake up wrecked. Talk to a doctor if:

• You snore loudly, or your wife has noticed you stop breathing for a moment.
• You wake gasping, or with a dry mouth and a headache.
• You get eight hours and still fall asleep in meetings or in front of the TV.
• You lie awake most nights for a month or more.

Sleep apnea is common, often goes undiagnosed, and is treatable. Insomnia has good treatment too, and a doctor can sort out what's behind it. Women in their forties and fifties sometimes find their sleep falls apart for hormonal reasons. What Actually Changes for Women in Their Forties and Fifties is a good place to start before the appointment. Some medications and conditions wreck sleep too, so bring a list.

The honest exceptions

Some seasons you can't win this. A newborn in the house. Night shifts. A parent in the hospital. Nobody's judging you for those.

But a backbone applies here too. If you've got a baby, split the nights with your wife so neither of you runs a deficit alone. One takes the first half, the other takes the second. Protect each other's stretch of sleep like it's money, because it is. If your job keeps stealing your evenings and your rest, it's fair to say so out loud and ask for a change.

And a debt you've run up on purpose is still a debt. Pay it back before it's asked for. Your family collects first.

Tonight, go to bed thirty minutes earlier than you did last night. Do it again tomorrow.