Most of us have pulled a short night to finish a project, study for an exam, or scroll through our phones in bed. It feels like a harmless sacrifice, something you can fix with strong coffee the next morning. Sleep specialists are warning that this casual attitude may be far more dangerous than it seems.
Spanish psychologist Nuria Roure, a specialist in sleep disorders, uses a blunt comparison to get people’s attention. She explains that staying awake for more than 20 hours and sleeping only four leaves your attention and concentration at a level similar to having drunk about six beers.
In her book ‘Por fin duermo’, and in the parenting podcast ‘Mami, ¿qué dices?’, she insists that sleep should matter as much as exercise, nutrition, and emotional balance.
What four hours of sleep does to your brain
Sleep experts use the term sleep deprivation for nights when we cut back far below our usual needs. Roure’s six beer comparison backs up what laboratory studies have seen for years.
Experiments in Australia and guidance from US public health agencies show that after 17 to 24 hours awake, people perform on attention tests as poorly as someone at or above the legal limit for alcohol behind the wheel.
That kind of impairment is not just an abstract number. It means slower reaction times, more errors at work, and worse judgment when you need it most, like during a late night drive or a sleepy early shift on the factory floor. In everyday terms, your brain is trying to get through the day with the lights half off.
Sleep also has a direct link with memory. During deep sleep, the brain strengthens new memories and clears out waste products that build up while we are awake.
Large studies suggest that regularly sleeping less than about six hours in midlife is associated with a higher risk of later cognitive decline and dementia, although scientists caution that sleep may be both a risk factor and an early warning sign.
A sleep debt that starts in the teen years
Adults are not the only ones running on empty. In many countries, including Spain, surveys find that people sleep around six and a half hours a night on average, below the seven to eight hours experts recommend. Teenagers often do even worse, going to bed late, waking up early for school, and building up a chronic sleep debt long before they step into the workforce.
Roure highlights that adolescents should be sleeping roughly nine hours each night for healthy brain and emotional development. Early school start times and homework that stretches into the evening make that target hard to hit.
The result shows up in classrooms as lower attention, mood swings, and grades that do not match a student’s real potential.
Screens add an extra layer of trouble. Bright white and blue light from phones and tablets in the late evening keeps the brain alert and suppresses melatonin, the hormone that signals it is time to sleep. Anyone who has meant to check one message and then fallen into an endless scroll until after midnight knows how easily one more video turns into a lost hour.
Health risks that add up over time
A short night here and there will not destroy your health, but regularly sleeping four to six hours carries clear long-term risks. Research links chronic poor sleep with higher chances of high blood pressure, type 2 diabetes, obesity, and heart disease, because the body has less time to repair blood vessels and regulate hormones that control appetite and metabolism.
For most people, that is the same cluster of problems they already worry about when they visit the doctor.
The immune system also pays a price. Studies show that people who sleep less are more likely to catch infections and take longer to recover, in part because key immune processes happen during the deepest stages of sleep. That can mean more sick days and more trips to the doctor for problems that might have been milder with better rest.
On top of that, repeated short nights appear to be linked with a higher risk of dementia later in life. Reviews of long-term studies report that people who consistently sleep around six hours or less in midlife are more likely to develop major neurocognitive disorders compared with those who sleep seven to eight hours, although not every study finds the same strength of effect.
Experts say the message is not to panic after a few bad nights, but to treat regular lack of sleep as a warning sign worth fixing.
Four simple habits to protect your sleep
Specialists recommend treating bedtime a bit like mealtimes. Going to bed and waking up at roughly the same hours every day helps your internal clock find a stable rhythm, so you feel sleepy at night and more alert in the morning. Over time, this routine can make it easier to fall asleep without tossing and turning.
Caffeine and heavy dinners quietly sabotage many people’s nights. Cutting off coffee, energy drinks, and strong tea by late afternoon, and choosing a lighter evening meal, gives your body a better chance to wind down.
Handling worries before getting into bed, for example by writing a to-do list or talking things through earlier in the evening, can keep racing thoughts from taking over the moment you turn off the light.
The glowing smartphone on the nightstand may be the hardest habit to change. Roure and other experts advise keeping screens out of the bedroom or at least switching them off well before sleep, since their light keeps the brain from sending the right signals to the rest of the body.
A cool, dark, quiet room then does the rest, letting sleep become what it really is, a basic form of daily maintenance that supports health, mood, and productivity far more reliably than another late night at the office.
The main work has been published in the official reports on sleep in Spain from the Spanish Sleep Society.
