Are you sitting right now? If you want to protect your brain, you should take a walk and be sure to go to bed early.

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Regular exercise and about seven hours of sleep a night could protect brain health in the long term, a study published Wednesday in the journal PLOS One found. Long bouts of sedentary behavior may increase dementia risk.

It’s the latest data to show that people don’t need elaborate and expensive longevity hacks to stay mentally sharp as they age. Simple lifestyle changes could reduce a person’s risk of late-onset dementia by as much as 25%, according to the study.

About 1 in 9 people in the United States will develop Alzheimer’s disease, according to the Alzheimer’s Association, meaning a person’s overall risk is about 11%. With the suggested changes in lifestyle, the average person’s risk decreases to about 8%.

The reduction is “fairly comparable to the effect sizes sometimes seen with medications for chronic diseases,” said Akinkunle Oye-Somefun, a researcher at York University in Toronto, who led the study.

Breaking up longer periods of sitting had the greatest effect, the study found.

“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,” said Phillip Hwang, an assistant professor of epidemiology at the Boston University School of Public Health, who was not involved in the study.

Researchers used data from 69 studies that included nearly 3 million people over eight decades. The average age of the people in the studies was 67 years old and they all resided in high-income countries, including the United States.

The studies — which followed people for at least a year, and sometimes as long as 11 years — measured how sleeping, sitting and activity habits starting at age 35 affected dementia risk later in life. Seventeen of the studies focused on sleep: The sweet spot for brain health was getting between seven and eight hours of sleep each night.

Sleeping less than seven hours increased dementia risk by 18%. Getting too much sleep –– more than eight hours per night –– increased dementia risk by 28%.

The rest of the studies in the analysis investigated dementia risk and either physical activity or sedentary behavior –– such as sitting at work for hours on end. Together, the studies showed that sitting for more than eight hours a day increased dementia risk by almost 30%, while regularly being active, even just going for a walk every day, decreased dementia risk by an average of 25%.

Moderate physical activity “offsets dementia risks even when other risk factors are present,” said Oye-Somefun.

Also, long periods of sitting can increase a person’s propensity to cardiovascular disease, diabetes and obesity, all of which raise dementia risk.

However, “many people assume that being physically active cancels out the harm of sitting for long periods. It doesn’t,” Oye-Somefun said. “We shouldn’t do one of these things alone, we should do them all.”

Indeed, exercising before work and then sitting for eight hours or more can erase some of the brain benefits of exercise, said Amal Wanigatunga, an assistant professor of epidemiology at

Johns Hopkins Bloomberg School of Public Health, who was not involved in the research.

Exercise boosts blood flow and oxygen to the brain

Breaking up long periods of sitting by standing or walking can improve brain blood flow, Wanigatunga said.

“The brain has these very small capillaries, so if there is reduced blood flow, especially to these very small pathways, that can be the bedrock for brain atrophy,” he said.

Muscle contractions — which occur when the body is moving — release a protein called brain-derived neurotrophic factor, or BDNF. That molecule boosts cognitive function, generates new neurons and improves connections between neurons, especially in the hippocampus, the part of the brain that converts short-term memory to long-term memory, Wanigatunga said.

Similarly, physical activity has been shown to reduce a peptide called beta-amyloid, which causes plaque to build up in the brain and may play a role in Alzheimer’s disease and dementia, Hwang said.

Exercise also reduces chronic inflammation in the brain, which hinders its ability to repair itself, Oye-Somefun said.

“Whatever the underlying cause for dementia might be, it does seem that physical activity can have a beneficial impact on the brain,” Hwang said.

A recent study suggested that staying mentally active while sitting, such as solving a puzzle or knitting, could help keep brains engaged even when someone is sedentary.

While activities that engage the brain could make sitting for long periods of time less detrimental than, say, watching TV, mental stimulation provides different protection for the brain than physical activity, making both things important, said Oye-Somefun.

Engaging in mentally stimulating activities works neural pathways in the brain, while exercise improves blood flow to the brain and prompts muscles to contract, Hwang said.

Both activities “are helping brain health in their own way,” he said.

Too much or too little sleep linked to dementia

There are some science-backed hypotheses about sleep and dementia.

First, sleep allows the brain’s glymphatic system to clean out waste, such as beta-amyloid, that accumulates during waking hours, similar to how the lymphatic system clears waste from the rest of the body, Hwang said. Spending the right amount of time in different stages of the sleep cycle, such as REM, may also help the brain consolidate memories.

It’s also possible that the answer is much simpler: A good night’s sleep makes it easier to manage stress, eat well and get enough exercise, he said.

“If you get a good night’s sleep, you have the means and the clarity and willpower to think about everything else, your activity, your diet,” said Johns Hopkins’ Wanigatunga. “You have to sleep no matter what, so try to improve that and then work on the rest of those behaviors.”

Finally, consistent physical activity is more important than intense exercise.

“Once you have it as a habit, you can refine it,” Wanigatunga said.