Sleep Week: Why Do I Need Sleep? And How Little Sleep Can I Get Away With?

It’s Be Well Philly Sleep Week! All week long, we’re celebrating sleep and all the wonderful things good quality shuteye does for your body. We reached out to Philly’s top sleep experts to answer all your sleep questions in one fell swoop. Check back this week for more installments of our ultimate sleep FAQ. And to see them all in one place, pick up a copy of Philadelphia magazine’s May issue, on newsstands now. 

Why do we sleep?

Surprisingly, nobody knows. “If I did, I’d be rich and famous,” laughs David Dinges, chief of Penn Med’s division of sleep and chronobiology. He adds that whatever sleep’s functions might be, it evolved because our planet has light and dark cycles every day: “Evolutionarily, it was adaptive to be out and about in one phase or the other. All animals function according to circadian rhythms, and sleep is a manifestation of that.”

That doesn’t mean there aren’t theories, of course; this is science! Richard Friedenheim, medical director of Abington-Jefferson Health’s sleep disorders centers, ticks off four: the restorative theory (“Sleep restores and revitalizes the body, so you wake up refreshed”); the energy-conservation theory (“At night, when there are fewer threats, you consume less energy so you can hold it over to when there are greater threats during the day”); the inactivity theory (animals evolved to be most active in whichever half of the cycle maximizes their survival); and the memory-consolidation theory (the sensory input from dreams stimulates neurons and synapses to help you learn). Whatever its purpose, says Dinges, scientists have established that nearly all complex life-forms sleep. How they sleep can differ. Dolphins, for example, can go for weeks with half the brain asleep and the other half awake, regularly switching the two sides off and on and seemingly maintaining constant vigilance.

What happens if I don’t sleep?

On the most basic level, says Friedenheim, “The drive to sleep is as strong as the drive to breathe.” Scientists have shown that if you keep rats from sleeping, they die in a matter of weeks: “You can feed them and feed them, but their temperature regulation goes down, their fur gets crunched up” — and they expire. People suffer as well. Studies have shown lack of sleep affects human metabolism, inflammation, heart health, cognitive effects, mood, even appetite (by increasing — ack! — the longing for sugar and carbs). “The immune system is perturbed,” says Sigrid Veasey, of Penn Med’s Center for Sleep and Circadian Neurobiology. And her research shows that chronic sleep deprivation destroys neurons in the brain — permanently. That’s not to mention the thousands of car accidents caused by nodding off at the wheel.

Okay, so how little sleep can I get away with?

That depends on your personal biochemistry. Human sleep needs, says Friedenheim, fall along a U-shaped curve. On one end are people who need very little sleep—say, four to six hours a night. On the other end are those who need 10 or more for optimal mood and performance. Interestingly, “Mortality increases on both ends of the curve,” notes Friedenheim. Getting too much sleep can be hazardous to your health, too. The Centers for Disease Control and Prevention have decreed that at least seven hours is optimal—and that a third of the country regularly gets less than seven hours’ sleep. In case you’re wondering, Penn researchers say work is the number one reason people cut back on sleep.

I only get six hours of sleep on weekdays, but I get eight hours on weekends. Won’t that make up for it?

Um. No. There’s a ton of research to prove it. “If you go two or three days on short sleep,” says Eric Sztejman, a pulmonologist with Virtua Health System, “you can be restored after one night of extra sleep and feel rested. But the literature doesn’t support going an entire week and catching up on the weekend.” You should establish bedtime rituals, according to our experts: “The brain is more inclined to sleep when given cues,” says David Greenspan, a psychiatrist at Einstein Medical Center. “Going to sleep and getting up at the same time seven days a week helps dramatically.” If that sounds too draconian, Thanuja Hamilton, a sleep doctor in South Jersey, says you can cheat occasionally—“but only by one hour.” So much for those Netflix marathons.

Older people sleep more than young people, right?

You probably know about REM and non-REM sleep, but sleep scientists further refine those stages. Non-REM 1, says Friedenheim, is a light, transitional sleep that’s skimpy in babies and much more frequent when you’re older. Non-REM 3 is the deep, highly restorative sleep that toddlers luxuriate in but that tapers off as we age. That’s because of deterioration in our sleep-wake neurons as we grow older, Veasey says, causing “a loss of the ability of the whole brain to be connected and to get deep sleep.” Nalaka Gooneratne, a Penn Med associate professor who studies sleep in the elderly, says science doesn’t yet know what drives the change. He does note that older adults have more opportunities for daytime sleep: “The consequences aren’t the same for them as if you fall asleep in a business meeting. The boundary between daytime sleep and nighttime sleep gets more blurred.” Studies also show that people who complain of difficulty sleeping frequently report they get less sleep than they actually do. When it comes to older friends and family, says Gooneratne, “The main thing to be worried about is a change in patterns.” If Mom always got seven hours of sleep but suddenly needs nine or is nodding off at lunchtime frequently, she should see a doctor: “There’s something else going on that needs to be addressed.”

Like what you’re reading? Stay in touch with Be Well Philly — here’s how: