Deep sleep – how long should it last?

Sleep proceeds in several repeating phases, which together form a cycle lasting approximately ninety minutes. First comes light sleep, during which the body gradually calms down and brain activity decreases. This is followed by deep sleep, which is the stage of most intense regeneration. After that comes the REM (rapid eye movement) phase, in which the brain is more active, vivid dreams are more likely to occur, and the body remains almost completely relaxed. These three stages repeat several times during the night.

1. Characteristics of deep sleep
2. Complete isolation from external stimuli
3. Factors disturbing deep sleep
4. The effects of lack of deep sleep
5. What supplements?

Characteristics of deep sleep

Deep sleep is the stage of sleep in which brain activity slows down most noticeably and brain waves take on a slow, regular rhythm called delta waves. The body then enters a state of intense regeneration, as muscle tension decreases, heart rate and breathing slow down, and the entire nervous system operates in economy mode. During this time, the body benefits from exceptionally stable physiological conditions, allowing tissues to rebuild and the immune system to function more effectively.

Complete isolation from external stimuli

It is also characteristic that during the deep sleep phase, it is easier to become completely isolated from external stimuli, which is why waking up from this stage can be more difficult, and sudden interruption of sleep can cause feelings of disorientation. This phase is considered crucial for memory and learning, as the brain organises information, strengthens neural connections and consolidates the most important experiences of the day. Deep sleep in a healthy adult should normally last between fifteen and twenty-five per cent of total sleep time.

Characteristics of different sleep phases

Factors disturbing deep sleep

Caffeine consumed too late

Sleep studies point to several major factors that disrupt the deep sleep phase. One of them is caffeine consumption. Even if coffee or tea is consumed several hours before bedtime, the caffeine they contain can prolong the time it takes to fall asleep, shorten the total amount of sleep, reduce the amount of deep sleep, and increase the number of awakenings.

Alcohol

Alcohol has a similar effect. Although it is initially associated with easier falling asleep, in practice it leads to fragmentation of night-time sleep, reduces sleep efficiency and disrupts the natural rhythm of passing through the phases, limiting the proportion of deep sleep.

Circadian rhythm disruption

Another important factor is the disruption of the circadian rhythm by irregular bedtimes and wake-up times, including shift work. People who work at night are less likely to achieve full stages of sleep, including deep sleep, which is associated with the biological clock not synchronising properly with sleep time. In addition to these factors, there is also exposure to artificial light and screens in the evening.

Artificial light

Light, especially blue light (emitted by computer and television screens), inhibits the body's natural preparations for sleep and can make it difficult to enter deep, restorative sleep. Sometimes, late and heavy meals or intense physical activity just before bedtime can affect deep sleep.

The effects of lack of deep sleep

When deep sleep is regularly disturbed, the body feels tired more quickly and it is more difficult to feel fully rested despite seemingly long periods of sleep. During the day, it is easier to experience poor concentration, slower thinking and greater irritability, because the nervous system does not have time to fully calm down. Immunity weakens, so infections occur more often. In some people, appetite regulation also changes, which encourages snacking and makes it difficult to maintain a stable body weight.

Analysis of human studies shows that deep sleep is most easily improved by methods that regulate the circadian rhythm and calm the body before night-time. Regular exercise, consistent sleep hours, dimmed lights in the evening and simple relaxation techniques create conditions conducive to regulating sleep phases. Cognitive behavioural therapy for insomnia often restores the natural architecture of sleep, making the deep phase longer and more continuous.

What supplements?

Melatonin supplementation mainly helps to regulate the time of falling asleep, thus indirectly promoting deeper sleep, while herbs with a calming effect improve calmness before bedtime, which in some people facilitates the natural deepening of slow-wave sleep. The nutritional status of magnesium, which regulates the excitability of the nervous system, may also be important.

Sources:

• Baglioni, C., Regen, W., Teghen, A., Spiegelhalder, K., Feige, B., Nissen, C., & Riemann, D. (2014). Sleep changes in the disorder of insomnia: a meta-analysis of polysomnographic studies. Sleep medicine reviews, 18(3), 195–213. https://doi.org/10.1016/j.smrv.2013.04.001
• Ohayon, M. M., Carskadon, M. A., Guilleminault, C., & Vitiello, M. V. (2004). Meta-analysis of quantitative sleep parameters from childhood to old age in healthy individuals: developing normative sleep values across the human lifespan. Sleep, 27(7), 1255–1273. https://doi.org/10.1093/sleep/27.7.1255
• Wickwire, E. M., Geiger-Brown, J., Scharf, S. M., & Drake, C. L. (2017). Shift Work and Shift Work Sleep Disorder: Clinical and Organizational Perspectives. Chest, 151(5), 1156–1172. https://doi.org/10.1016/j.chest.2016.12.007
• Poongkunran, C., John, S. G., Kannan, A. S., Shetty, S., Bime, C., & Parthasarathy, S. (2015). A meta-analysis of sleep-promoting interventions during critical illness. The American journal of medicine, 128(10), 1126–1137.e1. https://doi.org/10.1016/j.amjmed.2015.05.026