Sleeping for eight hours doesn't always mean getting the same quality of rest.
Although on paper going to bed at 10pm and waking up at 6am might seem the same as sleeping from 1am to 9am, sleep science shows that when we sleep has a major impact on how well we rest and how effectively our body recovers.
To understand why this happens, we spoke to Dr Celia García Malo, MD, PhD, a neurologist specialising in sleep medicine, who explains that our rest depends on far more than just the hours we spend in bed. While there isn't a single universal hour that works for everyone, finding your personal 'exact' bedtime comes down to understanding your unique chronotype.
The 10pm vs 1am dilemma: How your biological clock dictates sleep quality
The first thing to understand, notes the doctor, is that our sleep is governed by an internal biological clock—the circadian rhythm—which regulates body temperature, melatonin release, and incredibly complex metabolic, hormonal, and brain processes.
© Getty ImagesThat biological clock acts like an internal conductor, keeping the body in sync with natural cycles of light and dark. That’s why, when we stray too far from our natural sleep schedule, the body feels the strain—even if we've slept what feels like "enough".
"When we sleep in sync with our body clock, our rest tends to be far more restorative," Dr García Malo explains. "Our sleep cycles and stages remain stable, allowing normal physiological processes to take place properly."
Going to bed very late, however, can noticeably disrupt our sleep. "We might get the right number of hours, but at a time that's totally out of sync with our biology. On top of that, we become far more vulnerable to extra artificial light, particularly from screens," she notes.
The modern enemies of restorative sleep
This brings us to one of the biggest enemies of modern sleep: late-night overstimulation. Scrolling through your phone before bed, eating dinner late, or spending hours in front of screens can hamper the production of melatonin—the hormone that signals to the body it's time to sleep. The result is fragmented, less restorative sleep.
© Getty ImagesHowever, we don't all function in the same way. Some people feel full of energy first thing in the morning, while others hit their stride at night. "This is where chronotypes come into play," explains Dr García Malo. "Some people are naturally morning-oriented—functioning better when they go to bed and wake up early—while others are evening-oriented, sleeping and performing better later in the day."
Are you suffering from 'social jet lag'? How your chronotype holds the key
While it might seem that eight hours of sleep should yield the same results regardless of the time frame, our individual biology tells a different story.
"Getting a good night's sleep isn't just about counting hours — you have to think about quality, too. And the quality of your sleep depends largely on whether you turn in when your body is actually ready for it"
"The problem arises when our daily routines—work, school, artificial light, screens, and late dinners—force the body to sleep outside its natural biological window," says Dr García Malo. "Identifying someone's chronotype and trying to align their daily routine with their biological clock is the most effective way to ensure better rest. Looking into this can be incredibly helpful when treating insomnia."
In practice, this explains why so many people wake up feeling exhausted during the week despite getting eight hours of sleep, only feeling truly rested at weekends. This mismatch between societal demands and your body's natural clock creates a form of "social jet lag"—leaving you feeling sluggish, irritable and unfocused.
© Getty ImagesTo combat this, sleep specialists increasingly stress the importance of sticking to a consistent routine: aiming for regular bedtimes and wake-up times, cutting down on screen time before bed, and listening to your body's natural cues.
