While the link between poor sleep and dementia has long been known, it is not clear whether poor sleeping habits can cause dementia or whether poor sleep is an early symptom of dementia. However, new research reveals it sleep Quality can have a direct impact on rate where the brain is old.

“Our findings provide evidence that poor sleep may contribute to accelerated brain aging,” Explains 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 the quality of their sleep in five dimensions in 27,500 middle-aged and elderly people (average age 54.7 years) enrolled in the UK Biobank (a research institute that conducts long-term follow-up studies on the effects of genetic predisposition and lifestyle on the disease). Approximately nine years later, they scanned the participants’ brains using MRI and used machine learning models to estimate their biological brain age.

The researchers estimated sleep quality based on chronotype (morning or night), sleep duration, presence or absence of insomnia, presence or absence of snoring, and daytime sleepiness. Using these data, they classified the 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 reduction in the healthy sleep score, the difference between brain age and chronological age increased by approximately six months. The group with the poorest sleep quality showed that their brains were approximately one year older than their chronological age. This suggests that differences in sleep duration and sleep habits may affect the amount of brain age.

Researchers have found that a night-owl lifestyle, poor sleep duration (more than 7-8 hours), and snoring habits are particularly strongly associated with brain aging. They also found that the five factors that determine the quality of sleep 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 count, and the ratio of granulocytes to lymphocytes (a type of white blood cell), to analyze the role of inflammation in the relationship between sleep patterns and brain aging.

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

In addition to inflammation, there are many other ways that poor sleep can negatively affect the brain. One is its negative effect on the glymphatic system, which primarily removes waste from the brain during sleep. If the toxic substances in the brain are not effectively removed during sleep, it can damage the functioning of the nerve cells for a long time. Researchers also point out that poor sleep worsens cardiovascular health, which indirectly damages blood flow and brain tissue.

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