HIGH-INCOME COUNTRIES — Simple lifestyle changes — regular exercise, breaking up prolonged sitting, and getting about seven hours of sleep a night — could reduce a person's risk of late-onset dementia by as much as 25%, according to a meta-analysis published in the journal PLOS One. Researchers used data from 69 studies that included nearly 3 million people over eight decades to reach their findings.

The average age of participants across the studies was 67 years old, and all resided in high-income countries, including the United States. The studies followed people for at least a year and up to 11 years. The reduction in dementia risk associated with the lifestyle changes was comparable to the effect sizes sometimes seen with medications for chronic diseases, according to the study.

Among the behaviors examined, breaking up longer periods of sitting had the greatest effect on reducing dementia risk. Sitting for more than eight hours a day was associated with a nearly 30% increase in dementia risk. Long periods of sitting can also increase a person's risk of cardiovascular disease, diabetes and obesity, which all raise dementia risk, the study found.

"Many people assume that being physically active cancels out the harm of sitting for long periods. It doesn't," York University researcher Akinkunle Oye-Somefun said. "We shouldn't do one of these things alone, we should do them all."

Regular physical activity, even just going for a walk every day, was associated with an average 25% decrease in dementia risk. "You don't need to be perfect, but if you have a lot of sedentary time in your day, getting a bit of exercise, even if that's just going for a walk, will have a long-term benefit for the brain," Phillip Hwang, assistant professor of epidemiology at the Boston University School of Public Health, said.

Seventeen of the studies focused on sleep. Getting between seven and eight hours of sleep each night was associated with the lowest dementia risk. Sleeping less than seven hours per night was associated with an 18% increase in dementia risk, while sleeping more than eight hours per night was associated with a 28% increase.

About 1 in 9 people in the U.S. will develop Alzheimer's disease, according to the Alzheimer's Association. With the suggested lifestyle changes, the average person's risk of developing Alzheimer's would decrease to about 8%, according to the study. The findings were based on observational data, meaning a direct causal link between the lifestyle changes and reduced dementia risk cannot be definitively established.