Still staying up late and getting up late? The latest research: Sleeping like this increases the risk of dementia and accelerates aging!

Good sleep quality is the guarantee of good health. In the eyes of most people, sleeping 8 hours a day is the "gold standard" for good sleep. Sufficient sleep time is important, but for modern people, regular sleep is equally important, which is exactly what most people lack. Staying up late to play games, watch TV series, and sleep until noon on weekends is the norm for many people. Studies have found that this irregular sleep pattern is very harmful, even if you sleep 8 hours a day.

1. Irregular sleep may increase the risk of dementia

In December 2023, researchers published a study titled "Association of the Sleep Regularity Index With Incident Dementia and Brain Volume" in Neurology, analyzing the relationship between sleep regularity and dementia events. The researchers analyzed data from the UK Biobank, including 88,094 participants with an average age of 62 years, 56% of whom were women, and a total of 480 incident dementia cases during an average follow-up of 7.2 years.

Through the questionnaire, the researchers collected basic information such as the height, weight, and education level of the participants; life and work information such as smoking status, amount of exercise, working hours (day shift or night shift) and work status (employed or retired); history of chronic diseases such as depression, hypertension and diabetes and treatment history; family history of dementia; and information such as the presence of apolipoprotein Eε4 gene mutations. By having the participants wear monitoring devices for 7 consecutive days (1 week), the researchers collected the participants' sleep data, such as the time they fell asleep and the time they woke up, and used the sleep regularity index (SRI) to calculate their sleep regularity, that is, the consistency of their sleep-wake pattern every day. The total score of the sleep regularity index is 100 points, and the higher the score, the more regular the sleep.

In addition, the researchers also used magnetic resonance imaging to assess the participants' levels of brain health-related markers, including total brain volume, hippocampus volume, total gray matter volume, total white matter volume, and white matter high signal volume.

The results showed that the median sleep regularity index score of all participants was 60 points. During the 7.2-year follow-up period, a total of 480 new cases of dementia occurred. After adjusting for demographic, clinical and genetic confounders, there was a nonlinear association between SRI and dementia risk (p<0.001) (see Figure 1), and the hazard ratio (HR) followed a U-shaped pattern. Compared with participants with a sleep regularity index score of 60, the 5% of participants with the lowest score (average 41 points), that is, the 5% of participants with the most irregular sleep, had a 53% increased risk of dementia.

Figure 1 Relationship between sleep patterns and dementia risk

In addition, the study also found that compared with participants with a sleep regularity index score of 60, the 5% of participants with the lowest score had lower total gray matter volume and hippocampus volume. A reduction in gray matter volume can lead to a decline in cognitive function, an increased risk of mental illness, and problems with motor and sensory control. A reduction or damage to the hippocampus can lead to memory impairment, spatial orientation problems, and learning difficulties.

Conclusion: Sleep regularity is associated with dementia risk in a U-shaped manner. Irregular sleep may be a new risk factor for dementia.

The corresponding author of the study, Dr. Matthew P. Pase of Monash University, said that most people focus on the impact of short or long sleep duration on the risk of dementia, but rarely pay attention to the harm of irregular sleep. "Our results show that the association between sleep regularity and dementia is independent of sleep quality and duration. This suggests that sleep regularity is an important part of healthy sleep that we should pay attention to."

2. Irregular sleep makes the body more prone to premature aging

In August 2023, a study titled "Day-to-day deviations in sleep parameters and biological aging: Findings from the NHANES 2011-2014" published in Sleep Health showed that maintaining stable sleep habits can help slow down the biological aging process of the body. Compared with people with stable sleep habits, people with larger deviations in bedtime and large differences in sleep on weekdays and weekends are 9 months older in biological age.

Most previous studies have focused on the impact of average sleep parameters on lifespan. This study aimed to investigate the relationship between deviations in daily sleep parameters and biological age in 6,052 adults who participated in the 2011-2014 National Health and Nutrition Examination Survey. The study recorded daily deviations in sleep duration, efficiency, midpoint, and sleep parameters, including standard deviation of sleep time (sleep variability), standard deviation of sleep midpoint (sleep irregularity), catch-up sleep, and social jet lag. After adjusting for multiple covariates, it was observed that all parameters of daily sleep deviation were significantly associated with biological aging, and greater sleep variability, greater sleep irregularity, more catch-up sleep, and more social jet lag were associated with more advanced biological aging. Even after adjusting for sleep duration, efficiency, and midpoint, significant correlations between irregular sleep, catch-up sleep, and social jet lag and biological aging indices remained.

Conclusions: Daily deviations in sleep parameters are independently associated with biological aging in the US general population.

In addition to the duration, total time, and quality of sleep, increasing evidence suggests that daily deviations in the sleep-wake cycle are also critical for health. With the advancement of science and the increase in socioeconomic demands, we live in a 24-hour society, and daily variations in sleep patterns are common, and the impact of these variations on health cannot be ignored. Social jet lag and catch-up sleep are two common conditions characterized by significant differences in sleep timing or sleep duration between weekdays and weekends due to the demands of socializing, studying, or working. Both conditions have been associated with impaired cognitive ability, obesity, diabetes, cardiometabolic risk, and inflammation in adults.

Maintaining a regular sleep schedule is an easy-to-adjust lifestyle. With the application of various measuring devices and smartphones, people can find out whether they maintain a regular sleep schedule. For people with irregular sleep, measures should be taken to ensure the regularity of sleep and develop a regular bedtime and wake-up time to reduce the risk of dementia and aging.