Why is everyone tired?

Luke Barnard · September 15, 2026 · Presentation 2

Photo: ooneiroslyl / Unsplash

Show of hands

How many hours did you sleep last night?

Less than 6
6 to 7
7 to 8
8 or more

Teens need 8 to 10 hours. About 3 in 4 U.S. high schoolers get less than 8 on school nights.

CDC Youth Risk Behavior Survey; American Academy of Sleep Medicine

Sleep touches all six components

PhysicalGrowth hormone, immune repair, injury risk

MentalThe brain stores the day's memories during sleep. Cut the sleep and less of the day is kept.

EmotionalThe amygdala overreacts by ~60% when sleep deprived

SocialIrritability, misreading faces and tone

SpiritualChronic tiredness lowers motivation and the sense that anything matters

EnvironmentalDrowsy driving causes ~100,000 crashes a year

Yoo et al. 2007 (amygdala); NHTSA (drowsy driving estimate)

It's biology, not laziness

During puberty, the body's melatonin release shifts about 2 hours later.

School still starts at the same time.

Carskadon, adolescent circadian phase delay research

What sleep debt is

You need about 9 hours. Get 7, and you are 2 hours short. That shortfall does not disappear when you wake up. It carries over to the next night.

The body keeps count. A chemical called adenosine builds up every hour you are awake, and sleep clears it. Short sleep leaves some behind, and the leftover stacks up over the week.

In one study, two weeks of 6 hours a night produced the same test scores as two full nights with no sleep at all. The subjects rated themselves as only slightly tired.

You cannot bank sleep in advance, and one long night on the weekend repays only part of a week's debt.

Van Dongen et al. 2003, Sleep; Basheer et al. 2004 (adenosine and sleep pressure)

Do the math

Bed at Alarm at Hours slept - Short of 9 by - Debt by Friday -

Hours of debt by each school night, if every night looks like this.

What a week of debt does

Attention. In the 6-hour group, lapses kept climbing through day 14 and never leveled off.
Memory. The brain files new learning during sleep. A short night after studying keeps less of it.
Mood. Each hour of sleep a teen loses raises the odds of feeling hopeless by about a third.
Driving. Drowsy-driving crashes are most common among drivers under 25.

Paying it off with an all-nighter makes it worse. After 17 to 19 hours awake, reaction time matches a blood alcohol level of 0.05%.

Van Dongen et al. 2003, Sleep; Winsler et al. 2015, J. Youth and Adolescence; NHTSA; Williamson & Feyer 2000

What steals sleep

Caffeine. Half-life around 5 hours. Half of a 3 p.m. energy drink is still in you at 8 p.m.
The phone. The screen's light matters less than what's on it. Feeds are built to keep you scrolling past your bedtime.
Weekends. Sleeping in 3+ hours later than on school days is "social jet lag." Your body clock shifts by the same amount as a flight across two time zones, twice a week.

What actually helps

A fixed wake time, even on weekends. Matters more than bedtime.
Bright light in the first hour awake. Go outside.
Caffeine cutoff after lunch.
Phone charges outside the bedroom.
A 20-minute nap before 3 p.m. helps. A two-hour nap at 6 p.m. pushes bedtime later.

The bigger fix is public health

The American Academy of Pediatrics recommends middle and high schools start no earlier than 8:30 a.m.

California made it law in 2022. Early results: more sleep, better attendance, fewer car crashes involving teens in districts that shifted.

Our school at least clears the California minimum, so there is that.

The other fix is to show up late. I have tested this one personally.

AAP policy statement 2014; California SB 328; Wahlstrom et al. 2014 (school start time study)

Caffeine is not a substitute for sleep.

Questions?

Play the quiz

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