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Too Much of a Good Thing? Why Oversleeping Might Be Hurting Your Brain

June 18, 2025

We often hear about the dangers of not getting enough sleep—but what if getting too much sleep could also be harmful? New research suggests that consistently sleeping more than nine hours a night might not just leave you feeling groggy—it could impair your cognitive function and even your brain health in the long run.1

A global study led by Western University’s Brain and Mind Institute in Canada analysed data from over 40,000 participants and confirmed that the optimal sleep duration for cognitive performance was 7 to 8 hours per night.2 Both too little and too much sleep were associated with declines in memory, verbal ability, and problem-solving skills.2

Other recent studies echo these findings. Studies have found that long sleep duration – defined as more than nine hours per night – was linked to poorer cognitive performance.3 Specifically, memory, visuospatial ability, cognitive flexibility, and executive function (our brain’s ability to plan, focus, and make decisions) all took a hit.3

But why does more sleep pose a risk?

Part of the answer may lie in what often comes with excessive sleep. It has been associated with a 30% increased risk in global cognitive decline—and it’s also linked with other health issues. Long sleep duration has been tied to cardiovascular and cerebrovascular disease, as well as diabetes and metabolic syndrome—all of which are known risk factors for cognitive decline.4 These overlapping conditions may compound the impact on brain health.

Another theory is that excessive sleep leads to prolonged “sleep inertia”—that heavy, sluggish feeling after waking—which can blunt high-level thinking and decision-making.5 And while illness or low physical activity levels may contribute to long sleep, studies controlling for these factors still find that too much sleep alone can be detrimental.

The bottom line? Balance is crucial. While sleep is undeniably vital for health, more isn’t always better. The Global Council on Brain Health recommends 7 to 8 hours per night for adults—an amount that supports both physical and mental wellbeing.1

If you're regularly sleeping over nine hours and still waking up feeling tired, it might be time to check in with your doctor. It could be a sign of an underlying issue such as sleep apnea, metabolic dysfunction, or another treatable condition. Don’t ignore the signals—your brain health depends on it.

How Sove CPAP Clinic Can Help

Founded in 2008, Sove CPAP Clinic has grown to become a leading provider of respiratory and sleep services and products in Australia, with over 60 clinics nationwide. Our comprehensive clinical team includes Respiratory & Sleep Specialists, Sleep Technologists, and CPAP Consultants, ensuring that you receive comprehensive and personalised care. All medical procedures, including sleep studies and lung function testing, are bulk billed to all Australians, with minimal wait time.

If you would like to speak to a Respiratory & Sleep Physician, book a bulk-billed sleep study, or seek advice for your sleep apnea, you can reach us at 1300 76 29 39 or info@thecpapclinic.com.au.

ALWAYS FOLLOW THE DIRECTIONS FOR USE. CPAP is used for Obstructive Sleep Apnea treatment. When considering whether a sleep study or CPAP is right for you, speak to your doctor. Medicare criteria and T&Cs apply.

References

  1. Young, Vanessa M, et al. “Long Sleep Duration, Cognitive Performance, and the Moderating Role of Depression: A Cross‐Sectional Analysis in the Framingham Heart Study.” Alzheimer’s & Dementia, vol. 21, no. 4, 1 Apr. 2025, https://doi.org/10.1002/alz.70160.
  2. Newman, Tim. “Is Sleeping Too Much Bad for Your Brain?” Medical News Today, 12 Oct. 2018, www.medicalnewstoday.com/articles/323311#Real-world-implications.
  3. “Long Sleep Duration Is Associated with Lower Cognitive Function among Middle-Age Adults – the Doetinchem Cohort Study.” Sleep Medicine, vol. 41, 1 Jan. 2018, pp. 78–85, https://doi.org/10.1016/j.sleep.2017.07.029.
  4. Jaussent, Isabelle, et al. “Excessive Sleepiness Is Predictive of Cognitive Decline in the Elderly.” Sleep, vol. 35, no. 9, Sept. 2012, pp. 1201–1207, https://doi.org/10.5665/sleep.2070.
  5. “Does Too Much Sleep Have Negative Repercussions?” Psychology Today, 2018, www.psychologytoday.com/au/blog/the-athletes-way/201810/does-too-much-sleep-have-negative-repercussions. Accessed 18 June 2025.