Getting the Wrong Amount of Sleep and Sitting Too Much Could Raise Your Dementia Risk

The great news is that each of these factors is modifiable and within your control, says lead study author Akinkunle Oye-Somefun, PhD, a researcher at York University in Canada.

“What makes these findings compelling is the consistency of these associations,” says Dr. Oye-Somefun. “At a population level, that consistency has real implications for how we think about dementia prevention.”

How Movement and Rest Shape Dementia Risk

To examine how key health habits might impact brain health down the road, researchers reviewed data from 69 long-term studies involving millions of adults ages 35 and older, tracking physical activity, how much time people spent sitting, and sleep habits, before assessing who later developed dementia.

The results showed:

• People who were physically active on a regular basis had about a 25 percent lower risk of developing dementia, compared with sedentary adults.
• Sleeping less than seven hours a night was linked to about an 18 percent higher dementia risk, while sleeping more than eight hours was linked to about a 28 percent higher risk.
• Sitting for more than eight hours a day was tied to a 27 percent higher dementia risk.

“There’s a growing body of evidence linking everyday behaviors like physical activity, sleep, and sedentary time to cognitive health,” says Amal A. Wanigatunga, PhD, MPH, an assistant professor of epidemiology at the Johns Hopkins Bloomberg School of Public Health in Baltimore.

“What’s compelling about this study is that it brings together data from millions of people and shows a consistent pattern — these lifestyle factors are linked to dementia risk,” says Dr. Wanigatunga, who wasn’t involved in the research.

Physical activity is particularly important, according to the study authors. “A 25 percent lower risk of dementia associated with regular physical activity, applied across millions of people, represents a substantial number of diagnoses that may be preventable or delayed. That’s not a small effect,” says Oye-Somefun.

Wanigatunga agrees that physical activity is important, but he says that even people who get the recommended amount of exercise could still be at risk if they spend too much of the day sitting. “That’s the more novel piece of this analysis — that how long people spend sitting is independently linked to risk,” he says.

Because the studies followed people over time, they provide a stronger picture of how these habits may be linked to dementia risk, but because the findings are observational, they cannot prove cause and effect.

Sleep Plays a Complex and Important Role in Brain Health

During sleep, the brain clears out waste products and excess proteins that build up during the day — almost like a dishwasher for the brain, says Wanigatunga.

That process becomes most active during deep sleep, when the brain is working to flush out potentially harmful substances — including amyloid, a protein linked to Alzheimer’s disease, says Arman Fesharaki-Zadeh, MD, PhD, an assistant professor of psychiatry and neurology at Yale Medicine in New Haven, Connecticut.

“When sleep is consistently too short, that clearance system doesn’t function as well,” says Dr. Fesharaki-Zadeh, who wasn’t involved in the study.

Over time, that may allow these proteins to accumulate, which is one of the leading theories linking chronic sleep deprivation to dementia, he says.

“Very long sleep may be a signal that something else is going on in the body or brain, rather than a direct cause of dementia,” Fesharaki-Zadeh says.

Importantly, the findings should not be interpreted as strict sleep guidelines, says Oye-Somefun. While the study used seven to eight hours as the sleep benchmark, there’s still room for healthy variation.

If you’re worried you may be sleeping too much, he says, “Speak with your physician, rather than making abrupt changes based on population-level research.”

Why Movement and Sitting Less Are Good for Your Brain

Regular movement appears to support the brain in several ways, says Wanigatunga. “When you’re moving more, even just standing instead of sitting, you’re increasing blood flow and delivering oxygen and nutrients to important areas of the brain,” he says.

Muscle activity may also play a role. When muscles contract, they release substances that may help support brain function over time, he explains.

Expert Advice on Reducing Your Risk of Alzheimer’s Disease

The findings point to several habits that may support brain health over time — and Wanigatunga emphasizes that consistency matters most. “The hardest part is building the behavior. Life happens, but trying to build consistency first, and then optimizing later, 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 daily.
• Follow a Mediterranean-style diet.
• Get at least seven hours of sleep each night, and keep a consistent sleep schedule.
• Engage your brain through reading and intellectually challenging tasks.
• Stay socially engaged.