Scientists have pointed to the link between sleep quality and health risks

Sleep affects the well-being and functioning of the body, but its importance for health can be much broader than is commonly believed. Researchers have found a link between the characteristics of night rest and the risk of developing a variety of diseases, from cardiovascular to neurological. At the same time, not only the total duration of sleep is important, but also its phases, regularity and continuity. The information about which sleep characteristics were associated with the state of health and why the results do not yet allow us to talk about a direct cause-and—effect relationship is in the Izvestia article.

Sleep under supervision

The researchers analyzed data from 95,559 participants, whose average age was 56.2 years. The results of the study are published in the journal PLOS Medicine. To assess sleep, the researchers used readings from wrist accelerometers, devices that record human movements. Based on these data, using a machine learning algorithm, the scientists determined the duration of different sleep phases, the total duration of a night's rest, its regularity, and the waking time after falling asleep.

The participants wore the devices for seven days. The researchers then compared the results with data on new diagnoses registered during hospitalization and entered into the participants' electronic medical records. The median follow-up period was 8.9 years. In total, the researchers studied the relationship of sleep characteristics with 1,049 health indicators and found statistically significant associations with 156 diseases.

What phases of sleep are related to health?

One of the most noticeable patterns was the association of the duration of REM sleep with the risk of diseases. People who spent more time in this phase were less likely to have 83 diseases from different categories. These include heart failure, atrial fibrillation, coronary heart disease, dementia, Alzheimer's disease and Parkinsonism.

Longer deep sleep was also associated with a lower risk of certain diseases. This association was found for seven conditions, including type 2 diabetes, major depressive disorder, sleep apnea, and Parkinson's disease.

At the same time, the researchers took into account not only the absolute duration of the phases, but also other features of sleep. The results show that its structure can be related to the state of several body systems at once. However, they do not prove that increasing the duration of REM or deep sleep by itself protects against diseases.

Irregular sleep and nighttime awakenings

Separately, the scientists assessed the regularity of sleep and the waking time after falling asleep. Greater variability in sleep duration from day to day was associated with an increased risk of three conditions: anxiety disorders, major depressive disorder, and abdominal pain.

Prolonged wakefulness after falling asleep, in turn, was associated with an increased risk of six diseases. This indicator reflects the time that a person spends awake after initially falling asleep, including due to nighttime awakenings. Thus, it may not only be the number of hours spent in bed that matters. The continuity of night rest and the stability of the regime were also associated with the subsequent state of health of the participants.

How many hours of sleep is associated with lower risk

The duration of night rest was associated with the risk of 86 diseases according to a nonlinear model. For 69 of them, the values corresponding to the minimum risk were mainly in the range of six to eight hours of sleep. This group included, in particular, type 2 diabetes, dementia, chronic kidney disease and major depressive disorder.

The widest range of adverse associations was found in people who slept less than five hours. In this group, 37 out of 41 statistically significant associations with an increased risk of disease were recorded compared with participants who slept from six to eight hours.

However, the results do not mean that a sleep duration of six to eight hours guarantees the absence of diseases or is a universal norm for every person. The researchers assessed statistical patterns in a specific group of participants, rather than testing the effectiveness of a particular sleep regime.

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What the study does not allow to assert

The authors emphasize that the work was observational in nature. Therefore, based on its results, it is impossible to determine whether sleep disorders affect the development of diseases or, on the contrary, changes in night rest appear in the early stages of already developing pathologies.

In addition, sleep phases were determined using an algorithm that analyzes wrist movements. This method allows us to study sleep in a large number of people, but its estimates do not fully coincide with the results of polysomnography, a standard laboratory method for studying sleep. Therefore, the data obtained should be considered taking into account the limitations of the measurement method.

To test the likelihood of a reverse causal relationship, the researchers separately excluded cases of diseases detected within two years after the sleep assessment. After that, 95 of the original 156 associations remained statistically significant. This means that some of the patterns found could be explained by the fact that the disease was already developing and affecting sleep before diagnosis.

In addition, scientists do not exclude the influence of factors that are difficult to fully account for in an observational study. Therefore, the results expand the understanding of the relationship between sleep and health, but do not allow us to assert that changing its duration or structure alone will prevent the development of specific diseases.