If you’re sitting right now, the latest research has a simple message: get up, move a bit and get about seven hours of sleep.
A study published Wednesday in PLOS One found that regular exercise and about seven hours of sleep a night could protect brain health in the long term, while long bouts of sedentary behaviour may increase dementia risk.
The study said simple lifestyle changes could reduce a person’s risk of late-onset dementia by as much as 25 percent. About 1 in 9 people in the United States will develop Alzheimer’s disease, according to the Alzheimer’s Association, putting overall risk at about 11 percent. With the suggested lifestyle changes, the average person’s risk drops to about 8 percent.
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 biggest 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 involving nearly 3 million people over eight decades. The average age of participants was 67, and all lived in high-income countries, including the United States.
The studies followed people for at least a year, and in some cases as long as 11 years. They looked at how sleep, sitting and activity habits from age 35 affected dementia risk later in life.
Seventeen of the studies focused on sleep. The study found the best range for brain health was between seven and eight hours of sleep each night.
Sleeping less than seven hours increased dementia risk by 18 percent. Sleeping more than eight hours a night increased dementia risk by 28 percent.
The rest of the studies looked at dementia risk in relation to physical activity or sedentary behaviour, such as sitting at work for hours at a time.
Together, they found that sitting for more than eight hours a day increased dementia risk by almost 30 percent, while regular activity, even going for a walk every day, lowered dementia risk by an average of 25 percent.
Moderate physical activity “offsets dementia risks even when other risk factors are present,” Oye-Somefun said.
The study also noted that 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.”
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.
Wanigatunga said exercise boosts blood flow and oxygen to the brain. He said breaking up long periods of sitting by standing or walking can improve brain blood flow.
“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.
Wanigatunga said muscle contractions during movement release a protein called brain-derived neurotrophic factor, or BDNF. He said it 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.
Physical activity has also 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.
But Oye-Somefun said mentally stimulating activities and physical activity protect the brain in different ways. Hwang said mentally stimulating activities work neural pathways in the brain, while exercise improves blood flow to the brain and prompts muscles to contract.
Both activities “are helping brain health in their own way,” he said.
On sleep, researchers pointed to several possible explanations. Hwang said sleep allows the brain’s glymphatic system to clear out waste such as beta-amyloid that builds up during waking hours. Time spent in different sleep stages, including REM, may also help the brain consolidate memories.
He also said a simpler explanation may apply. A good night’s sleep can make it easier to manage stress, eat well and get enough exercise.
“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.”
Wanigatunga said consistency matters more than intensity when it comes to exercise.
“Once you have it as a habit, you can refine it,” Wanigatunga said.
Read more from NBC News.