Poor sleep quality accelerates brain aging

While the link between poor sleep and dementia has long been known, it was unclear whether poor sleep habits could cause dementia or whether poor sleep was an early symptom of dementia. However, new search revealed that sleep quality can have a direct impact on the speed at which the brain ages.

“Our results prove that poor sleep can contribute to accelerated brain aging,” explain Abigail Dove, a neuroepidemiologist at the Karolinska Institute in Sweden, “and points to inflammation as one of the underlying mechanisms.”

High correlation with night owl lifestyle and snoring

Researchers assessed their sleep quality along five dimensions in 27,500 middle-aged and elderly people (average age 54.7 years) enrolled in the UK Biobank (a research institute conducting long-term follow-up studies into the effects of genetic predisposition and lifestyle on the disease). About nine years later, they scanned the participants’ brains with an MRI and used machine learning models to estimate their brain biological age.

The researchers quantified sleep quality based on chronotype (morning or evening), sleep duration, presence or absence of insomnia, presence or absence of snoring and daytime sleepiness. Using this data, they categorized participants into three sleep patterns, finding that 41.2 percent had healthy sleep, 3.3 percent had clearly poor sleep, and 55.6 percent fell into the middle group.

The analysis showed that for every point of decrease in healthy sleep score, the difference between brain age and chronological age increased by approximately six months. The group with the worst sleep quality showed that their brains were about a year older than their chronological age. This suggests that differences in sleep duration and sleep patterns can significantly affect the rate at which the brain ages.

Researchers have found that a nocturnal lifestyle, unhealthy sleep duration (beyond 7 to 8 hours), and snoring habits are particularly strongly associated with brain aging. They also found that the five factors that determine sleep quality interact with each other. For example, insomnia can lead to excessive daytime sleepiness, and a nocturnal lifestyle can lead to shorter sleep times.

Poor sleep leads to chronic inflammation in the body

To understand the mechanism by which poor sleep affects the brain, the research team also measured the level of low-grade inflammation in the body. Specifically, they used a combination of biomarkers, such as C-reactive protein levels, white blood cell and platelet counts, and the granulocyte-to-lymphocyte ratio (a type of white blood cell), to analyze the role of inflammation in the relationship between sleep patterns and brain aging.

The results confirmed that higher levels of inflammation in the body tend to increase brain age. Mediation analysis (a method of analyzing the influence of intervening variables in the causal relationship between two variables) found that inflammation explained about 7 percent of the association between intervening sleep patterns and brain aging, and more than 10 percent of the association with poor sleep habits. In other words, it is very likely that poor sleep quality facilitates the appearance of chronic inflammation in the body, which accelerates brain aging.

In addition to inflammation, poor sleep can negatively affect the brain in several other ways. The first is its negative impact on the glymphatic system, which primarily removes waste from the brain during sleep. If toxic substances present in the brain are not eliminated effectively during sleep, this could in the long term impair the functioning of nerve cells. Researchers also pointed out that poor sleep can worsen cardiovascular health, which indirectly damages blood circulation and brain tissue.

This story originally appeared in WIRED Japan and was translated from Japanese.