The habit of going to bed after 11:00 p.m. damages the brain and leads to obesity

We live in an era of chronic sleep deprivation. According to the World Health Organization, more than a third of people in developed countries regularly sleep less than the recommended 7–9 hours a day. And one of the main reasons is going to bed late. Many people believe that the total number of hours of sleep is what matters most. But scientists are increasingly emphasizing that:

The time it takes to fall asleep is just as important as the duration of sleep

Why? Because our bodies operate on an internal biological clock—circadian rhythms. And around 11:00 p.m., this clock begins to trigger key recovery processes. If you’re still awake at that time, the chain of biochemical reactions is disrupted—and the consequences accumulate week after week.

What Happens Immediately: A Hormonal Imbalance

As darkness falls, the pineal gland in the brain begins to produce melatonin—the “night hormone.” Melatonin levels peak between approximately 11:00 p.m. and 2:00 a.m. Melatonin is not just a signal to go to sleep. It regulates the antioxidant defense of cells, the immune response, and even counteracts the growth of certain tumors.

If you’re awake during its peak—especially with bright lights or screens on—melatonin production is suppressed. At the same time, cortisol, the “stress hormone,” begins to rise. Normally, cortisol levels should be at their lowest at night and rise sharply as you wake up in the morning. Sleeping late disrupts this rhythm, leaving the body in a state of chronic, low-level stress.

Weeks 1–2: Muscle soreness and recovery

Growth hormone (somatotropin) is secreted almost exclusively during deep sleep—especially during the first sleep cycles of the night. It is responsible not only for growth in children, but also for:

• recovery of muscle fibers after physical activity;

• renewal of skin cells and internal organs;

• regulation of fat metabolism;

• maintaining bone density.

A study published in the *Journal of Sleep Research* found that people who regularly go to bed after midnight have 20–30% lower levels of nighttime growth hormone compared to those who fall asleep before 11:00 p.m. This is particularly critical for athletes and teenagers.

Week 3: The brain stops cleansing itself

One of the most remarkable scientific discoveries of the past decade is the existence of the brain’s glymphatic system. It is a kind of “sewer system” for the central nervous system that is most active during sleep.

During sleep, cerebrospinal fluid flushes the intercellular spaces of the brain, washing away toxic metabolites—primarily beta-amyloid and tau protein. It is the accumulation of these substances that is linked to the development of Alzheimer’s disease and other neurodegenerative disorders.

A 2019 study published in *Science* showed that the glymphatic system is most active during slow-wave (deep) sleep—and it is precisely this phase that people who go to bed late miss out on. A disruption in the brain’s “nighttime cleanup” is not a metaphor. Neurotoxins literally accumulate in neurons, accelerating their death.

Week 4 and beyond: hunger hormones spiral out of control

Leptin and ghrelin are two key hormones that regulate appetite. Leptin signals to the brain that you are full, while ghrelin signals that you are hungry. The balance between them is largely determined by the quality of your sleep.

Chronic sleep disturbance leads to:

• a decrease in leptin levels (the brain does not receive the "I'm full" signal);
• an increase in ghrelin levels (a constant feeling of hunger);
• an increased craving for high-calorie foods—fatty, sweet, and salty foods.

A large-scale study involving more than 68,000 women (the Nurses’ Health Study) found that those who slept less than 5 hours a day weighed, on average, 2.5 kg more than those who slept 7–8 hours. And it’s not just about the amount: going to bed later is in itself linked to weight gain—regardless of how long you sleep.

What to Do: Practical Recommendations

The good news is that circadian rhythms can be adjusted. Here are a few scientifically proven steps:

• Go to bed at the same time every night—even on weekends. An irregular sleep schedule is just as harmful as going to bed late.
• Dim the lights 1–2 hours before bedtime. The blue light emitted by screens significantly suppresses melatonin production.
• Don't eat 2–3 hours before bedtime. Eating late shifts your circadian rhythm toward wakefulness.
• Bright light in the morning “resets” your body clock and makes it easier to fall asleep at the right time the following night.
• Limit your caffeine intake after 2:00 p.m. The half-life of caffeine is about 6 hours.

Sleep is not a passive state of inactivity. It is the period of the body’s most active recovery, which cannot be “made up for” or replaced by anything else. Every night you stay up late doesn’t just leave you tired the next day. It creates a biochemical debt that your body will take years to pay off.

Sources: WHO Global Sleep Report, Journal of Sleep Research, Science (2019), Nurses’ Health Study (Harvard T.H. Chan School of Public Health)