A lack of good quality sleep has long been linked to an increased risk of developing dementia, but new research goes further – giving us an optimal amount of overnight slumber to minimize dementia risk later in life.
Using data gathered and pooled from 69 previous studies, a team from York University in Canada ran a statistical analysis to look for associations with dementia for three different factors: physical activity, time spent sitting, and sleep duration.
These are all variables we can control ourselves, up to a point, and the number crunching showed that between 7 and 8 hours of slumber each night was the sweet spot when it came to minimizing dementia risk.
In addition, the researchers found that prolonged sitting (more than 8 hours a day) and a lack of physical activity (less than 150 minutes a week) were also linked to a significant increase in the chances of getting dementia.
"Regular physical activity, less sedentary time and appropriate nightly sleep (7 to 8 hours) may be associated with reduced risk of dementia and are potentially modifiable factors in the prevention or delay of dementia," write the researchers in their published paper.
Getting less than 7 hours of shut-eye a night was linked to an 18 percent increase in dementia risk, while getting more than 8 hours a night correlated to a 28 percent increase.
Those findings align with previous studies: Getting too much sleep can be as harmful to our health as getting too little. If you want a target to aim for, then somewhere between 7 and 8 hours seems best.
The researchers emphasize that their review doesn't prove cause and effect, though – these are associations, not direct connections.
What's more, clarifying between triggers and consequences can be tricky: There's research to suggest that sleeping too much is a sign that Alzheimer's has already started, for example, and not just a driver for the disease.
Add in the physical activity connection and recommendations around sitting too much – both previously linked to issues with brain health – and it seems we have a collection of behaviors that are good for the brain.
Although the researchers didn't conduct any testing themselves, they point to the benefits of exercise, regular movement, and sleep in maintaining active blood flow in the brain, clearing waste from neurons, and protecting other parts of the body linked to the brain (such as the heart).
With no cure yet available, and the number of dementia cases expected to keep on rising in the coming years, experts are keen to look at ways that people can limit their chances of developing diseases such as Alzheimer's in the first place.
It's estimated that around half of all cases could be avoided by addressing lifestyle risk factors.
"Taken together, a healthy movement behavior profile may promote vascular, neurotrophic, and anti-inflammatory effects that collectively support brain health and may delay the onset or progression of dementia," write the researchers.
One of the benefits of the research is the sheer number of people included: almost 4.5 million, all told. It's also notable that the data here cover people down to age 35, a much younger starting point than in many other studies on dementia.
All of the reviewed studies followed participants from a dementia-free starting point and then assessed the incidence of dementia over time.
However, there are limitations too. The reviewed studies varied significantly in terms of data collection and collation, and there were more figures on some behaviors than others – only 3 of the 69 studies looked specifically at sedentary habits, for example.
Gathering more data on the link between dementia risk and spending too much of the day sitting could be one avenue for future studies, the researchers suggest.
Related: Simple Blood Test Can Predict Dementia Risk in Women Decades Before Symptoms
"Future studies with middle-aged adults and longer-term follow-up, including changes in movement behaviors over time, are needed to better understand the relationship between physical activity, sedentary behavior, and sleep for dementia risk," write the researchers.
The research has been published in PLOS One.