Sleep, regularity beats hours: the new paradigm of sleep health

There is no 'magic' number of hours of rest for everyone. Science points to regular rhythms and the reduction of chronic stress as keys to health and prevention

25 September 2025

3' min read

Key points

Regularity beats quantity
Stress, the real enemy of sleep
Flies and robots in the lab
The associations between poor sleep and illness

3' min read

Beware of 'sleep terrorism': sounding the warning is Giorgio Gilestro, sleep neurobiologist, associate professor at the Department of Life Sciences, Imperial College London. 'Sleep terrorism is a widespread tendency to turn poor sleep into a threat: if you don't sleep seven hours a night, you will get cancer, diabetes, dementia and other diseases'.

Regularity beats quantity

Sleeping too little or too long has long been linked to an increased risk of premature mortality, and it is precisely sleep duration that has remained at the centre of health guidelines. But today, research opens up a new front: what really matters, for various clinical outcomes, may be the regularity of the sleep-wake rhythm, even more than the number of hours spent in bed.

Supporting a less rigid view on the 'ideal number of hours slept' is a 2023 study of almost 61 thousand participants from the UK Biobank. The researchers calculated a Sleep Regularity Index by analysing more than 10 million hours of tracking collected with accelerometers (which record movements day and night, allowing them to tell when a person is asleep and when they are awake), with an average follow-up of 6.3 years. The results show that a more regular sleep-wake rhythm is associated with a significantly lower risk of mortality: 20-48% less for all causes, 16-39% less for cancer and 22-57% less for cardiometabolic diseases, compared to the group with the most irregular rhythms. Regularity proved to be a stronger predictor than duration: in other words, going to bed and waking up on a consistent schedule seems to protect more than the 'classic' eight hours of sleep.

Stress e cervello: che rapporto c’è?

Stress, the true enemy of sleep

Leading a laboratory dedicated to the study of the molecular and behavioural mechanisms of sleep, Gilestro also came to the conclusion through his analyses that it is not 'how many hours we sleep', but rather the role of stress and the quality of rest that influences our health.

Gilestro points out that insomnia sufferers mainly benefit from behavioural therapy. In these courses, the psychotherapist does not ask to increase the hours of sleep, but to reduce the anxiety associated with not sleeping. "Don't stress about it", is the basic rule: the less one worries about staying awake, the less the problem affects one's daily life. By reducing stress, sleep tends to become more continuous and performance during the day improves, even if the amount of hours remains reduced.

Flies and robots in the lab

In order to explore the relationship between sleep and health, Gilestro's lab has developed robotic tools that allow the flies' sleep to be interrupted only when they are actually asleep, minimising stress. "Unlike traditional methods (vibrations, treadmills, even electric shocks in rats), these systems make it possible to distinguish the effect of sleep deprivation from that of stress induced by the experiment," the researcher explains. With this technology, he started sleep deprivation in three-day-old flies and continued it throughout their lives. The result was surprising: longevity does not change. Sleep deprivation throughout life did not reduce the life expectancy of the insects.

Another study, published by the Imperial College professor's group, questioned the concept of sleep homeostasis, i.e. the tendency to recover lost sleep. In male flies, for example, entire days of wakefulness without any sleep are observed during courtship. But when the female is removed, the male does not feel the need to 'catch up' with the lost hours. If, on the other hand, sleep is artificially interrupted by robots or other males to fight with, then yes, a strong rebound is observed.

Sognare per capire, creare e (forse) decidere

The associations between poor sleep and illness

'This shows that it is not the quantity of sleep lost that determines recovery, but the quality and context in which it is lost,' says the Italian researcher. 'Many of the associations between poor sleep and disease could be explained precisely by chronic stress, which is itself a cause of inflammation, metabolic imbalances and psychological vulnerability. Disturbed sleep thus becomes a symptom of stress, rather than its cause'.

In terms of public health, recalls Giorgio Gilestro, therapies should aim at reducing stress rather than chasing a fixed number of hours slept; and in communication, it is necessary to avoid alarmist messages that risk fuelling anxiety and worsening insomnia problems, while in health policies, it makes more sense to work on factors that reduce work, social and environmental stress, promoting regular and stable routines that reduce the biological and psychological stress linked to altered rhythms and indirectly also promote better sleep.

"Sleep remains a basic biological need, but it should not be separated from the overall picture of mental health and living conditions. What makes the difference is the quality of sleep and, above all, how we learn to manage stress.