Sleep and mental health

I often tell myself that I will “recover on the weekend” or that “sleeping less saves time”. However, the science is clear: sleep is not a negotiable luxury. It is an active and fundamental biological process, during which my brain consolidates learning, regulates emotions, eliminates neuronal metabolic waste and restores hormonal balances. According to a study published in Sleep Medicine Reviews (2019), people with chronic insomnia have a 2.5-fold increased risk of depression and a 3.5-fold increased risk of anxiety disorder. Understanding this bidirectional link between sleep and mental health, and acting on it, is one of the most profitable health investments I can make.

1. What happens in my brain while I sleep

Sleep is organized in cycles of approximately 90 minutes, repeated 4 to 6 times per night. Each cycle alternates several stages with distinct and complementary functions:

Light slow-wave sleep: transition between wakefulness and deep sleep. Phase of gradual slowing down of brain and muscular activity.

Deep slow-wave sleep: major physical recovery phase. Tissue growth and repair occur here. The brain's glymphatic system eliminates metabolic waste accumulated during the day, including beta-amyloid proteins, implicated in Alzheimer's disease.

Paradoxical sleep (REM): intense dream phase. Crucial for the consolidation of learning, emotional regulation and the treatment of traumatic experiences. This is where the brain “cleans” the emotional load of the day.

Lack of sleep, even partial and chronic, disrupts all of these processes, with measurable consequences on mood, cognition, the immune system and metabolism.

2. The bidirectional link between sleep and mental health

The link between sleep and mental health is bidirectional: sleep disorders aggravate psychological disorders, and psychological disorders worsen sleep. This vicious circle is one of the central challenges of preventive mental health.

3. Identify the enemies of my sleep

Before acting on my sleep, it is useful to identify the factors that disrupt it. The most documented among active people are:

• ●Screens in the evening: blue light from smartphones and computers inhibits the secretion of melatonin (the sleep hormone) for 2 to 3 hours. Exposed to a screen at 10 p.m., I delay my natural falling asleep until midnight.

• ●Stress and ruminations: a high cortisol level in the evening prevents you from falling asleep. Intrusive work-related thoughts keep the brain on alert despite physical fatigue.

• ●Irregular schedules: shifting your bedtime or waking up time on the weekend disrupts the biological clock (circadian rhythm) and generates “social jet lag” with effects comparable to real jet lag.

• ●Alcohol: frequently taken as an aid to falling asleep, alcohol actually fragments sleep in the second half of the night and suppresses paradoxical sleep, reducing emotional recovery.

• ●Caffeine: its half-life is 5 to 7 hours. A coffee at 4 p.m. still represents the equivalent of half a coffee of caffeine at 10 p.m. in my body.

4. Validated strategies to improve my sleep

Regularity above all. Going to bed and getting up at the same time 7 days a week (including weekends) is the most effective measure for stabilizing my circadian rhythm. Consistency of schedule is more important than sleep duration.A logout routine. The 60 minutes before bed are decisive. I turn off the screens, dim the lights, read, listen to soft music, or practice a few minutes of mindful breathing. This routine signals to my brain that sleep time is approaching.

An optimized environment. The room should be cool (18-19° is the ideal temperature), dark and quiet. Body temperature must drop slightly to trigger sleep; a room that is too hot keeps it high and delays sleep.

CBT-I for chronic insomnia. Cognitive and behavioral therapy for insomnia (CBT-I) is the standard treatment recommended by the HAS for chronic insomnia, more effective in the long term than sleeping pills, without the side effects.

Physical activity. Regular exercise improves the quality and depth of sleep. Warning: intense physical activity less than 3 hours before bedtime can have the opposite effect by raising body temperature and cortisol.

5. When to consult for sleep disorders?

I consult my general practitioner if I have one of the following criteria:

• ●Difficulty falling asleep or frequent nocturnal awakenings for more than 3 months, at least 3 nights per week.

• ●Significant daytime fatigue despite sufficient sleep duration (possible sleep apnea or other disorder).

• ●Sleep problems accompanied by depressed mood, marked anxiety or a notable alteration in my quality of life.

A health check-up including an assessment of sleep, perceived duration, quality, daytime sleepiness, allows problems to be identified early before they become chronic and have a lasting impact on mental health.