Poor sleep hygiene seems to raise the likelihood of dementia over time, especially when problems with sleep are severe or long lasting. Researchers now see unhealthy sleep as one of several lifestyle risks that can be changed to help protect brain health.
What “poor sleep hygiene” really means
Sleep hygiene is the set of daily habits and environment cues that shape how well you sleep. Poor sleep hygiene can include things like going to bed at wildly different times every night, using phones in bed, drinking a lot of caffeine late in the day, or ignoring loud noise and light in the bedroom. Over time, these habits can lead to:
• Trouble falling asleep
• Waking up many times during the night
• Very short sleep or very long, unrefreshing sleep
• Heavy reliance on sleeping pills
• Sleep problems such as insomnia, sleep apnea, or a very irregular sleep–wake schedule
Scientists focus less on the individual habit and more on the end result: years of poor quality sleep or not enough sleep.
How poor sleep is linked to dementia risk
Several large studies suggest that long term sleep problems raise dementia risk by around 10 to 20 percent, especially when people regularly sleep less than about six hours a night.[5] This is not as strong a risk factor as age or genetics, but it is important because sleep patterns can be improved.
A study in the American Journal of Preventive Medicine followed over 6,000 adults aged 65 and older for about 10 years.[1] People who often had trouble falling asleep, a form of insomnia, were a little more than 50 percent more likely to develop dementia than those who fell asleep easily.[1] Regular use of sleeping medication was linked with about a 30 percent higher dementia risk.[1] This does not prove that insomnia or sleeping pills directly cause dementia, but it does show a clear association.
Other research has examined sleep duration and self reported sleep quality in people with mild cognitive impairment, a condition that often comes before dementia.[4][6] These studies found that very long sleep duration and poor sleep quality were associated with higher rates of later dementia in this group.[4][6] The relationship is complex, because changes in the brain before dementia may also disturb sleep, but the link is strong enough that scientists are taking sleep seriously as a risk factor.
Sleep patterns, circadian rhythm, and dementia
It is not only how long you sleep that matters, but also when and how regular your sleep is. Your circadian rhythm is your internal 24 hour clock that helps set daily patterns of sleep and activity.[3] When this rhythm is weak or constantly disrupted by shift work, late nights, or irregular schedules, it may affect brain health.
In one study reported in the journal Neurology, researchers monitored the sleep and daily activity patterns of more than 2,000 older adults.[3] None had dementia at the start. Over time, those with the weakest, most irregular circadian rhythms were almost two and a half times more likely to develop dementia than those with the strongest rhythms, even after adjusting for age and health problems.[3]
The timing of daily activity also mattered. People whose daily activity peaked later in the afternoon, around 2:15 p.m. or later, had a 45 percent higher risk of dementia compared with those whose activity peaked earlier in the day.[3] This suggests that late, irregular schedules may be a warning sign or a contributor to future brain problems.
Why sleep is so important for the brain
During deep sleep, the brain does important maintenance work. One key process is the clearing of waste products that build up during the day. A brain “cleaning system” called the glymphatic system becomes more active in deep sleep and helps flush out proteins such as beta amyloid, which is closely linked to Alzheimer’s disease.[2]
When sleep is too short, fragmented, or poor in quality, this cleaning process does not work as well.[2] Harmful proteins can build up, and the brain experiences more inflammation, oxidative stress, and cell damage, all of which promote neurodegeneration.[2] Over many years, this may make dementia more likely.
Poor sleep also affects memory directly. Sleep is vital for consolidating new memories and supporting thinking skills.[2][5] When sleep is disturbed again and again, people may notice word finding problems, difficulty focusing, or slower thinking. While these issues do not always mean dementia, they may add to other brain stresses and lower the brain’s ability to cope with damage.
Specific sleep disorders and dementia
Some sleep problems are not just bad habits but actual medical disorders, and several of them have been linked with higher dementia risk.
• Insomnia
Chronic insomnia is more than just a few bad nights. It is persistent trouble falling asleep, staying asleep, or waking too early with daytime tiredness. The study in the American Journal of Preventive Medicine found that sleep initiation insomnia increased the risk of dementia by just over 50 percent.[1] Other reviews report that long term poor sleep quantity or quality leads to about a 10 to 20 percent higher risk of dementia.[5] Long standing insomnia may raise stress hormones, disturb circadian rhythms, and hurt neuron health, which together can promote depression and Alzheimer’s disease.[2]
• Sleep apnea
Sleep apnea causes repeated pauses in breathing during sleep, which lower oxygen levels. Over time, this reduced oxygen can injure brain cells, harm blood vessels, and lead to memory problems.[2] Untreated sleep apnea has been associated with higher risks of cognitive impairment and possibly dementia, especially when severe.[2]
• Fragmented or very irregular sleep
Even without insomnia or apnea, people whose sleep is extremely broken or whose sleep–wake times change dramatically from day to day may be at higher risk. The Neurology study of circadian rhythms suggests that weak, irregular rhythms are strongly tied to later dementia.[3]
Is poor sleep a cause or an early symptom?
One of the hardest questions is whether poor sleep hygiene causes dementia or is simply an early warning sign of brain changes that are already underway. The truth is likely both.
On one hand, processes that lead to Alzheimer’s disease, such as accumulation of beta amyloid and tau, can disturb the brain regions that regulate sleep and circadian rhythms. That means new sleep problems in an older adult can sometimes be an early sign of silent brain changes.
On the other hand, studies where people are followed for many years show that long lasting poor sleep comes before dementia in many cases.[1][5] Experimental research also shows that disrupting deep sleep raises beta amyloid levels in the brain, and improving sleep can reduce them, at least in the short term.[2] Taken together, most experts believe that poor sleep increases risk and that early dementia changes also worsen sleep, creating a harmful cycle.
How much sleep seems protective
Most adults need about 7 to 9 hours of sleep each night for good health.[2] Regularly getting less than 6 hours has been linked to higher dementia risk in several studies.[2][5] Too much sleep may also be a concern. In some research with older adults who already had mild cognitive problems, very long sleep duration was associated with a greater chance of progressing to dementia.[4][6] Very long sleep can sometimes signal underlying illness or more advanced brain changes.
The goal is not to sleep as
