By Sara Bright
Sleep has become a cultural obsession. We track our REM cycles on smartwatches, invest in weighted blankets, and ritualise bedtime routines as though they were sacred ceremonies. Yet beneath this collective pursuit of rest lies a paradox that few wish to confront: too much sleep may be quietly destroying our health. A growing body of international research now suggests that chronic oversleeping is not merely a harmless indulgence but a genuine medical risk – one that mirrors, and in some measures exceeds, the dangers of sleep deprivation itself.
The Scale of the Problem
The World Health Organization estimates that roughly one-third of adults globally experience insomnia at some point in their lives, and approximately ten per cent suffer from chronic sleep disorders. But while public health campaigns have long hammered home the message that we are not sleeping enough, the opposite end of the spectrum has received scant attention. Hypersomnia – a condition characterised by excessive daytime sleepiness despite sleeping for twelve or more hours in a twenty-four-hour period – remains significantly underdiagnosed and poorly understood.
“A society that worships the eight-hour night may be producing a generation of over-sleepers who mistake quantity for quality,” says Dr Moira Junge, Chief Executive of the Sleep Health Foundation. “Oversleeping is not simply laziness. For many people, it is a symptom of something deeper – and for others, it is actively making things worse.”
The numbers are striking. According to a landmark meta-analysis published in the journal GeroScience in June 2025, regularly sleeping more than nine hours per night is associated with a thirty-four per cent increase in the risk of death from all causes. The study, conducted by researchers at Semmelweis University in Budapest, drew on seventy-nine international publications encompassing more than two million participants. The findings were unambiguous: sleeping nine hours or more nightly carried a higher mortality risk than sleeping fewer than seven hours, where the increase stood at fourteen per cent.
The Cardiovascular Price of Extra Sleep
The relationship between prolonged sleep and heart disease has long troubled researchers. A comprehensive systematic review published in Sleep Medicine Reviews, which analysed data from over five million participants across one hundred and thirty-seven prospective cohort studies, found that long sleep duration was associated with a forty-six per cent increased risk of stroke, a twenty-five per cent greater likelihood of cardiovascular disease, and a twenty-four per cent elevated risk of coronary heart disease.
The mechanisms are still being untangled, but chronic inflammation appears to be a central culprit. Extended periods spent in bed can promote systemic inflammatory responses – a known driver of arterial stiffness, hypertension, and atherosclerosis. In April 2025, the American Heart Association formally expanded its “Life’s Simple Seven” cardiovascular health framework to include sleep as an eighth core component, a landmark acknowledgement that rest is not peripheral to heart health but integral.
“What we are seeing is that sleep operates on a J-shaped curve,” explains Dr Kelsie Full, a behavioural epidemiologist at Vanderbilt University Medical Center. “Both too little and too much push us away from the optimum. The sweet spot for most adults remains seven to eight hours, and deviations in either direction carry measurable consequences.”
Full’s own research, published in JAMA Network Open in February 2025, tracked nearly forty-seven thousand adults over more than twelve years. The study found that people whose sleep durations fluctuated outside the healthy range – consistently sleeping well beyond seven to nine hours – faced a twenty-nine per cent higher risk of death from all causes. The effect was observed across racial groups and income levels, though it proved strongest among white participants and those with household incomes above fifteen thousand dollars.
When the Brain Pays the Price
The cognitive toll of chronic oversleeping may be the most alarming dimension of the emerging evidence. A study published in Alzheimer’s and Dementia in April 2025 examined sleep duration and cognition in nearly two thousand adults aged twenty-seven to eighty-five. Researchers found that those sleeping nine hours or more nightly performed worse on tests measuring memory, visual-spatial skills, and executive function. The association was particularly pronounced among participants with symptoms of depression, regardless of whether they were taking antidepressant medication.
Separate research presented at the 2025 Alzheimer’s Association International Conference by Dr Alberto Ramos, Director of the Sleep Disorders Programme at the University of Miami, reinforced these findings. Ramos and his team analysed data from the Hispanic Community Health Study and found that long sleep duration over a fourteen-year period was linked to progressive neurocognitive decline – even after adjusting for sleep apnoea, which can independently drive both short and long sleep durations.
“The relationship between sleep and the brain is not linear,” Ramos noted. “What may begin as a behavioural pattern can, over time, become a marker of neurodegeneration. We need to take prolonged sleep seriously as a potential early indicator.”
A large-scale study published in eBioMedicine in October 2025, which leveraged neuroimaging data from more than twenty-seven thousand UK Biobank participants, added a further dimension. Poor sleep health was associated with accelerated brain ageing, and systemic inflammation was identified as a key mediating mechanism. Participants with the least regular sleep patterns showed the most pronounced age-related changes in brain structure – including cortical thinning, hippocampal volume reduction, and compromised white matter integrity.
The Mental Health Feedback Loop
Oversleeping is both a symptom and a catalyst of psychological distress, creating a feedback loop that can be exceptionally difficult to break. Depression and anxiety are strongly associated with prolonged sleep, yet excessive rest can deepen the very conditions that trigger it. Disrupted circadian rhythms alter the production of cortisol and melatonin, hormones essential for mood regulation, while extended periods of inactivity compound feelings of lethargy and disengagement.
The Sleep Foundation reports that insomnia increases the risk of depression by up to fivefold, while between eighty and ninety per cent of people with clinical depression also experience sleep disturbances. In the UK, where sleep deprivation costs the economy an estimated thirty-seven billion pounds annually in lost productivity according to RAND Europe, the psychological burden of dysfunctional sleep is immense.
What makes oversleeping particularly insidious is its cultural acceptance. While chronic insomnia carries visible social stigma – the fatigued colleague, the bleary-eyed parent – long sleep is often envied. Weekend lie-ins, “catching up” on rest, and the romanticisation of the duvet day are woven into the fabric of British leisure culture. Yet the evidence suggests that these very habits may be destabilising the circadian rhythms on which mental health depends.
Gender, Age, and Vulnerability
Not all long sleepers face equal risk. The Semmelweis meta-analysis revealed notable sex-based disparities: men sleeping eight hours or more nightly experienced a thirty-six per cent increase in mortality risk, while women in the same category faced a forty-four per cent rise. The reasons remain under investigation but may relate to hormonal differences, variations in inflammatory response, and divergent cardiovascular profiles.
Age compounds the equation. A study published in Sleep Health in 2023, tracking three-year sleep trajectories in patients with type 2 diabetes, found that those whose sleep consistently exceeded the optimal range had significantly elevated risks of both all-cause and cardiovascular mortality. The combination of long sleep with advanced age, insulin use, and elevated blood pressure produced compounding effects – individuals over sixty-five who slept outside the recommended window faced mortality risks up to four times higher than their better-rested peers.
For postmenopausal women, the picture is equally concerning. A systematic review published in the International Journal of Women’s Health in January 2026 found that both short and excessively long sleep was associated with attention difficulties and slower information processing, with women sleeping more than eight hours experiencing the most pronounced cognitive impairments.
Reclaiming the Balance
The emerging consensus among sleep researchers is clear: consistency trumps duration. The NHS recommends that adults aim for seven to nine hours of sleep per night, maintained at roughly the same times on weeknights and weekends. A UK Biobank study published in eLife in 2023, which tracked nearly eighty-nine thousand participants using accelerometry, found that irregular sleep patterns were associated with a fifty-three per cent increase in all-cause mortality compared with those who maintained consistent sleep-wake cycles.
Practical interventions are straightforward. Keeping the bedroom dark, cool, and quiet; limiting screen exposure in the hour before bed; and engaging in regular daytime physical activity all support healthy circadian function. Avoiding alcohol and late-day caffeine remains essential. Crucially, experts advise against the temptation to “make up” for lost sleep at weekends – a practice that, paradoxically, can deepen the cycle of dysfunction.
If persistent oversleeping continues despite improved habits, a visit to a GP is warranted. Hypersomnia can signal underlying conditions ranging from thyroid disorders and chronic fatigue syndrome to obstructive sleep apnoea and depression. The NHS advises that anyone regularly falling asleep during the day, despite sleeping long hours at night, should seek medical evaluation.
Sleep, it turns out, is less a destination than a discipline. In a culture that increasingly frames rest as self-care, the evidence demands a more nuanced conversation – one that recognises the fine line between restoration and risk. The goal is not to sleep more, but to sleep better. And that distinction may matter more than we ever imagined.
Related: Why Women Need More Sleep Than Men | 8-Hour Sleep: Is It Really Beneficial for Everyone?
