Why your Sleep Schedule is Accelerating Cognitive Decline

Here’s how to fix it.

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My Longevity Experiment
October 08, 2024

The Optimal Amount of Sleep for Mental Health and Cognitive Performance

Sleep is essential for life, much like eating, but there are plenty of ways to get it wrong. Recent research has shed light on the optimal amount of sleep needed for mental health, cognitive performance, and overall well-being. A new study, analyzing a cohort of nearly 500,000 adults, has delved into how sleep duration affects individuals, particularly those aged 38 to 73 years.

Findings from the Latest Study

Researchers from Fudan University in China, led by neuroscientist Yuzhu Li, and from Cambridge University, led by psychiatry researcher Barbara Sahakian, published a study examining data from 498,277 participants as part of the UK Biobank study. Of these participants, approximately 48,500 underwent neuroimaging, while nearly 157,000 completed an online mental health follow-up questionnaire. This extensive data pool allowed the researchers to assess how the amount of sleep individuals get correlates with various aspects of their mental and brain health.

In their findings, the researchers state, "We identified a nonlinear association between sleep, with approximately seven hours as the optimal sleep duration, and genetic and cognitive factors, brain structure, and mental health as key measures." Their longitudinal analysis revealed that both insufficient and excessive sleep were significantly associated with cognitive decline over time.

The U-Shaped Curve: Too Much or Too Little Sleep

The research discovered a U-shaped curve when it comes to sleep duration and its effects. Those who slept too little experienced diminished cognitive function and mental health, but the same was true for individuals who slept excessively, sometimes up to 12-13 hours a day.

Thanks to the inclusion of neuroimaging data, the researchers could explore whether genetic and brain structural mechanisms played a role in these findings. Their modeling suggests that genetics and brain structure do contribute to the effects of sleep, but further research is needed to confirm these mechanisms.

Professor Jianfeng Feng, Dean of the Institute of Science and Technology for Brain-Inspired Intelligence at Fudan University, highlighted the implications of the study, stating, "While we can't say conclusively that too little or too much sleep causes cognitive problems, our analysis looking at individuals over a longer period of time appears to support this idea. But the reasons why older people have poorer sleep appear to be complex, influenced by a combination of our genetic makeup and the structure of our brains."

Key Takeaways and Caveats

While the study offers significant insights, it comes with a few caveats. As an observational study, it demonstrates associations rather than proving causality. It remains unclear whether sleeping more or less than seven hours directly causes issues with mental health or cognitive function, or whether these issues lead to abnormal sleep patterns. Furthermore, the research does not suggest that sleeping six or eight hours will drastically impact well-being; the primary focus is on extremes in sleep duration, such as one hour or 13 hours a night.

The data show that sleep duration, cognitive function, and mental health have a significant nonlinear association. Seven hours of sleep appears to be the sweet spot in the middle of this curve.

However, Professor Sahakian cautioned against making drastic changes based on the study's findings: "If you don't feel refreshed unless you get eight hours of sleep a night, don't try to wake up an hour earlier and expect to get the health benefits."

The study emphasizes the importance of aiming for seven hours of sleep as individuals age, with Sahakian adding, "Getting a good night's sleep is important at all stages of life, but particularly as we age. Finding ways to improve sleep for older people could be crucial to helping them maintain good mental health and wellbeing, and avoiding cognitive decline, particularly for patients with psychiatric disorders and dementias."

Limitations of the Study

The study does have certain limitations. For example, it only assessed total sleep duration and did not account for other measures of sleep quality, such as waking during the night, deep sleep, or REM sleep. Additionally, participants self-reported their sleep duration, which was not objectively measured using sleep tracking devices. Nevertheless, the large sample size lends robustness to the study’s conclusions.

Previous Research on Sleep Duration

This study builds on previous research that has consistently highlighted the importance of sleep duration for health. Past studies have linked poor sleep quality and shorter sleep duration in older adults to a higher risk of developing dementia or early death. Other research has also connected sleeping fewer than six hours a night with an increased risk of cardiovascular disease.

It has become a standard recommendation to aim for around seven hours of sleep per night. Prior studies have suggested that individuals should not sleep before 10 PM, should aim to fall asleep no later than 11 PM, and definitely avoid going to bed after midnight. This recent study further supports the idea that seven hours of sleep is optimal, particularly as people enter middle and older age.

In conclusion, while sleep requirements may vary among individuals, targeting seven hours per night appears to be a beneficial goal for maintaining mental health and cognitive performance, especially as we age.

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