With the holiday season in full swing and to-do lists piling up, many people are struggling to get enough rest — but experts say the number of hours you sleep may not be the whole story.
While adults are often advised to sleep seven to nine hours a night, studies show that getting less than seven hours can raise the risk of obesity, hypertension, heart disease, and other health problems. CNN also previously reported that five hours or less of sleep can significantly increase the chances of chronic illness.
But according to clinical psychologist Dr. Tony Cunningham, director of the Center for Sleep and Cognition in Boston, focusing strictly on sleep duration misses a major part of the equation.
Why Sleep Quality Matters as Much as Sleep Time
Cunningham told CNN that two key biological forces control how well we sleep:
- Sleep pressure, which builds the longer we’re awake
- Circadian rhythm, our internal body clock
Sleep pressure works like hunger — the longer you go without sleep, the more your body craves it. Ideally, you should only get into bed once this sleep drive has built up.
Circadian rhythm, meanwhile, signals when the body should feel awake or sleepy. It can override tiredness temporarily, such as during an all-nighter when people experience a “second wind.”
For optimal rest, both systems must be aligned — which is why irregular schedules or abrupt changes can disrupt sleep quality even if you hit the recommended number of hours.
Cunningham suggests waking up at the same time every day, which helps stabilize the circadian rhythm more effectively than forcing yourself to sleep at a fixed hour.
Do You Really Need 8 Hours? Not Everyone Does
While seven to nine hours is the standard recommendation, Cunningham says sleep needs vary widely.
Some people function best with just five or six hours, while others naturally require nine to eleven hours to feel rested.
To determine your ideal amount, Cunningham advises:
- Choose a bedtime when you’re actually sleepy, not just tired. If you can’t fall asleep within 20–30 minutes, get up and do a calming activity with dim lighting.
- Find a few days when you can wake naturally without an alarm. Block external light, hide clocks, and remove time cues. Sleep until your body wakes on its own.
The first few nights may include long stretches of sleep as your body catches up on lost rest. But once you wake naturally at the same time for several days, that’s a strong sign you’ve found your true sleep need.
While not everyone has the flexibility to try this, Cunningham says students on break or adults taking time off may find it useful — especially if they’re worried about chronic tiredness.
