The great news is that each of these factors is changeable and under your control, says the study’s lead author, Dr. Akinkunle Oye Samphan, a researcher at York University in Canada.
“What makes these findings so compelling is the consistency of these associations,” says Dr. Oye-Samphan. “At a population level, that consistency has a big impact on how we think about dementia prevention.”
How exercise and rest shape dementia risk
To find out how important health habits influence future brain health, researchers reviewed data from 69 longitudinal studies of millions of adults over the age of 35, tracking their physical activity, time spent sitting, and sleep habits, and assessing who subsequently developed dementia.
The results showed the following:
- People who engaged in regular physical activity had about a 25 percent lower risk of developing dementia compared to sedentary adults.
- They found that sleeping less than 7 hours increased the risk of dementia by about 18%, and sleeping more than 8 hours increased the risk by about 28%.
- It was found that sitting for more than eight hours a day increased the risk of dementia by 27 percent.
“There is growing evidence linking daily behaviors such as physical activity, sleep, and sedentary time to cognitive health,” says Amal A. Wanigatunga, Ph.D., MPH, assistant professor of epidemiology at the Johns Hopkins Bloomberg School of Public Health in Baltimore.
“What’s fascinating about this study is that it brings together data from millions of people and shows a consistent pattern: These lifestyle factors are associated with dementia risk,” says Wanigatunga, who was not involved in the study.
Physical activity is particularly important, according to the study authors. “The 25% reduction in dementia risk associated with regular physical activity, applied to millions of people, represents a significant number of diagnoses that could be prevented or delayed. This is no small effect,” Oye-Somefan says.
Wanigatunga agrees that physical activity is important, but says even people who get the recommended amount of exercise can still be at risk if they spend much of the day sitting. “This is the more novel part of this analysis: The amount of time people spend sitting is independently associated with risk,” he says.
Because the study followed people over a long period of time, it provides a more detailed picture of how these habits are related to dementia risk, but the findings are observational and cannot prove causation.
Sleep plays a complex and important role in brain health
Wanigatunga says that during sleep, the brain gets rid of waste products and excess protein that have accumulated during the day. It’s like a dishwasher for your brain.
This process is most active during deep sleep, when the brain is working to eliminate potentially harmful substances, including amyloid, a protein associated with Alzheimer’s disease, says Arman Fesharaki-Zadeh, MD, assistant professor of psychiatry and neurology at Yale Medicine in New Haven, Connecticut.
“If you consistently sleep too little, your clearance system won’t work as well,” says Dr. Fesharaki Zadeh, who was not involved in the study.
Over time, these proteins can accumulate, he says, and this is one of the leading theories linking chronic sleep deprivation to dementia.
“Extremely long sleep may not be a direct cause of dementia, but may indicate that something else is going on in the body or brain,” Fesharaki-Zadeh says.
Importantly, the study results should not be interpreted as strict sleep guidelines, Oye-Somefan says. Although this study used 7 to 8 hours as a sleep benchmark, there is still room for healthy variation.
If you’re worried you’re sleeping too much, “talk to your doctor instead of suddenly making changes based on population-level studies,” he says.
Why moving your body and reducing your sitting time is good for your brain
Wanigatunga says regular exercise appears to support the brain in a number of ways. “Moving your body more, even by just standing instead of sitting, increases blood flow, which delivers oxygen and nutrients to important areas of the brain,” he says.
Muscle activity may also play a role. He explains that when muscles contract, they release substances that may support brain function over time.
Expert advice to reduce your risk of Alzheimer’s disease
The findings point to some habits that may support brain health over the long term, and Wanigatunga stresses that consistency is paramount. “The hardest thing is building behavior. A lot of things happen in life, but building consistency first and then optimizing is really the goal,” he says.
Fesharaki Zadeh recommends the following habits to reduce the risk of dementia later in life:
- Aim for at least 20 minutes of aerobic exercise each day.
- Stick to a Mediterranean-style diet.
- Get at least 7 hours of sleep each night and maintain a consistent sleep schedule.
- Activate your brain through reading and intellectually challenging tasks.
- Stay connected to society.
