Trouble sleeping may raise your risk of dementia later in life, according to a new 19-year study of over 22,000 middle-aged and older adults in Sweden.
Both insomnia symptoms and shorter sleep were linked to higher chances of developing dementia down the road.
Key facts:
- Adults reporting insomnia symptoms had an 18% higher risk of being diagnosed with dementia during the study compared to those without insomnia.
- Shorter sleep duration was also associated with increased dementia risk. Getting 6 hours of sleep or less raised the risk by about 25-30% compared to getting a “normal” 8 hours.
- But the study found insomnia only raised dementia risk in people who slept at least 7 hours per night. Short sleepers with insomnia did not have any additional risk versus short sleepers without insomnia.
- Difficulty falling asleep, but not other insomnia issues like trouble staying asleep, was tied to higher dementia odds.
Source: Age and Ageing (2023 Sep; 52(9).
The Brain-Sleep Connection
Sleep is crucial for brain health. As we sleep, our brains clear out waste and toxic proteins. Poor sleep deprives the brain of this important “cleaning” time.
Studies suggest short or disrupted sleep allows these waste products to build up.
Over time, this may stress and damage brain cells, contributing to cognitive decline and dementia.
Research also indicates poor sleep negatively impacts parts of the brain involved in memory formation and learning.
Lack of quality sleep may prevent the brain from properly storing new information.
So scientists have been trying to pin down whether common sleep troubles like insomnia and short sleep duration may increase dementia risk later in life.
The Study and Who Was Involved
The research followed over 22,000 Swedish adults for around 19 years on average. All participants were aged 46 or older when the study began.
In 1997, the participants filled out questionnaires about:
- Insomnia symptoms like trouble falling asleep, staying asleep, or waking too early
- How many hours they slept per night
- Other factors like depression, activity levels, smoking, etc.
Over the next 19 years, the researchers tracked who developed dementia using national health records.
This allowed them to relate sleep issues reported at the study start to eventual dementia diagnoses.
Overall Findings on Insomnia, Short Sleep and Dementia
About 16% of participants had insomnia symptoms at the outset.
During follow-up, people reporting insomnia were 18% more likely to develop dementia than those without insomnia.
Shorter sleep was also linked to higher dementia odds.
Getting 6 hours of sleep or less nightly raised dementia risk by 25-30% compared to “normal” 8 hour sleepers.
But when the researchers looked closer, they found insomnia only increased risk in folks getting at least 7 hours of sleep.
For short sleepers (<7 hours), having insomnia did not further raise their already-elevated dementia likelihood.
Insomnia Type Matters
Not all insomnia symptoms posed the same dementia risk.
Only trouble falling asleep was linked to higher chances of eventually developing dementia.
Other issues like trouble staying asleep were not tied to dementia risk in this study.
Why this difference? We don’t know for sure.
But earlier research found trouble falling asleep specifically is linked to poorer function in brain areas involved in memory and learning.
This could be one reason it raises dementia risk more than other insomnia issues.
The Interplay Between Insomnia & Short Sleep
This study highlights that both insomnia and short sleep on their own can negatively impact brain health.
But together, these sleep issues appear to interact in complex ways that modify dementia risk over the long-term.
For people sleeping less than 7 hours, insomnia did not further increase their already-high dementia likelihood.
But insomnia did raise risk in folks getting at least 7 hours of sleep.
This suggests short and long sleepers may face different risks related to insomnia. There are a few potential reasons why:
- People tend to overestimate how much they actually sleep. Short sleepers especially may sleep even less than they report. So “7 hours” of sleep with insomnia may end up much shorter in reality.
- Even for accurate 7+ hour sleepers, insomnia reduces time spent in crucial deep, restorative sleep stages. This appears detrimental even if total sleep duration seems otherwise normal.
- Long sleepers with insomnia (9+ hours) may get poor quality sleep. Research links extended, restless sleep to higher dementia odds.
Overall, both insomnia and short sleep duration contribute to poorer sleep quality.
This seems to damage cognitive health regardless of how long someone is actually sleeping.
Why Do These Sleep Issues Increase Dementia Risk?
Researchers don’t fully understand the mechanisms linking insomnia and short sleep to cognitive decline and dementia.
But several factors likely contribute:
Reduced Brain “Cleaning”
As we sleep, our brains clear out waste and toxins. Insomnia and short sleep limit this crucial cleaning time.
Built-up proteins and waste may stress and damage brain cells over time. This is a suspected early contributor to Alzheimer’s and dementia.
Disrupted Memory Consolidation
Deep, quality sleep is when memories get cemented and stored in the brain. Insomnia and short sleep disrupt this memory consolidation process.
Over time, the inability to properly store new information may facilitate cognitive decline.
Increased Inflammation
Poor and insufficient sleep raise inflammation levels in the body and brain.
Chronic inflammation damages neurons and may drive plaque buildup in Alzheimer’s disease.
Vascular Damage
Insomnia and sleep loss are linked to hypertension, diabetes, stroke risk – issues that damage the brain’s blood vessels.
Vascular damage can starve the brain of oxygen, leading to cognitive impairment and dementia.
Hormone Imbalances
Deep sleep regulates hormones like cortisol and growth hormone that support neuron health.
Disrupting deep sleep alters these hormone levels, which may ultimately harm cognition.
Who Might Be at Risk?
This study involved middle-aged and older Swedish adults.
The findings suggest that adults in this age range face higher chances of cognitive decline and dementia if they regularly get poor quality and/or insufficient sleep.
Certain groups may be more vulnerable to dementia risk from sleep issues:
- People with sleep disorders like insomnia, sleep apnea
- Those with mental health issues that disrupt sleep like anxiety, depression
- Individuals working non-standard shifts that lead to poor sleep
- Anyone experiencing major sleep disruption on a chronic basis
Implications and Future Studies
This study highlights that both insomnia and short sleep are modifiable risk factors for cognitive decline and dementia.
Treating sleep problems could be an important strategy for supporting long-term brain health.
But many open questions remain around how normal age-related changes in sleep interact with dementia risk over time. Areas for future research include:
- How do other aspects of sleep quality besides duration influence dementia risk – like time in restorative deep sleep stages?
- Does the relationship between sleep issues and dementia risk change across different age groups – like young-old versus oldest-old adults?
- Can treating sleep disorders and insomnia lower dementia likelihood, or just slow cognitive decline?
- What sleep habits optimized for cognitive health look like at different ages.
Relationship between sleep & dementia
This long-term Swedish study provides compelling evidence that common sleep troubles raise the odds of eventually developing dementia.
Both insomnia symptoms and short sleep duration were linked to higher dementia risk over nearly two decades of follow-up.
However, the relationship between sleep and dementia likelihood is complex.
The impact of insomnia seems to depend on sleep duration.
More research is needed to clarify these interactions and optimize sleep habits for long-term brain health.
But the takeaway is clear: prioritizing healthy, restorative sleep is crucial for supporting cognitive function as we age.
Talk to your doctor if you regularly have insomnia or other sleep issues that may jeopardize your brain health down the road.
Treating sleep problems could be key for dementia prevention.
References
- Study: Interactive association between insomnia symptoms and sleep duration for the risk of dementia
- Authors: Xiao Tan et al. (2023)
