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A new �첥��Ƶ-led study considers how the ways people move, sit and sleep are related to onset of dementia.

With people living longer than ever before, dementia is becoming a common part of aging worldwide.

Parmis Mirzadeh, a Faculty of Health doctoral candidate in kinesiology and health science, says “Dementia is a growing global public health challenge, with over 50 million people affected worldwide and numbers expected to rise substantially in the coming decades.”

Despite its prevalence, Mirzadeh explains, there is still no cure for the condition and existing treatments have only limited effects. As a result, researchers increasingly see prevention as a critical response; however, preventing a condition that develops slowly, often over decades, requires a better understanding of how routine, potentially changeable habits influence risk over the long term.

While previous research links exercise and sleep to dementia, the evidence has often been fragmented. Few large reviews have examined physical activity, sedentary behaviour and sleep collectively – particularly in middle‑aged adults, when prevention efforts may be most effective.

“Understanding how these everyday behaviours relate to dementia risk earlier in the life course can help inform prevention strategies because they can be targeted through public health and clinical interventions,” says Mirzadeh.

Mirzadeh and Akinkunle Oye-Somefun, a recently graduated PhD student, have addressed this gap with a new study published in which was supervised by Chris Ardern, Faculty of Health associate dean of research and innovation.

The �첥��Ƶ-led team conducted a systematic review and meta‑analysis of dozens of long‑running cohort studies dating back to the 1940s and representing millions of adults aged 35 and older. “It provided an opportunity to better understand how daily habits like physical activity, sedentary time and sleep collectively shape brain health over time,” says Mirzadeh.

The study suggests that how people move and rest across the day may be one important piece of protecting brain health as populations age.

The study pooled results across this research to identify consistent patterns among the nearly three million participants included in the analysis. Clear associations emerged across each of the movement patterns examined.

Researchers found that people who met standard physical activity guidelines – roughly 150 minutes of activity per week – had about a 25 per cent lower probability of onset dementia compared with those who were inactive.

The analysis also found that those who slept substantially less than seven hours per night, as well as those who regularly slept more than eight hours, were more likely to experience onset dementia than those who slept seven to eight hours. Longer sleep duration showed the strongest association, echoing earlier research suggesting it may reflect underlying health or early neurological changes.

Sedentary habits proved to be one of the more difficult areas to analyze. “One of the more surprising findings was how sparse the data remains for sedentary behaviour, despite it being recognized as a distinct health risk for more than a decade,” says Mirzadeh. Even so, the available research points to a consistent pattern: individuals who spent eight hours or more per day sitting are more likely to develop dementia.

Taken together, the findings suggest that staying physically active, limiting long periods of sitting and getting a moderate amount of sleep are each associated with better brain health over the long term.

The authors stress that these findings show associations, not cause and effect. Being active or sleeping well does not make someone immune to dementia and factors such as genetics, education and overall health still play major roles. The researchers also note limitations in the available evidence and call for future studies that track movement and sleep over time using objective tools like wearable devices.

Even so, the patterns were strong and consistent enough to matter.

“We hope this work helps raise awareness that everyday behaviours such as physical activity, sedentary time and sleep are associated with brain health,” says Mirzadeh. “Because these are modifiable, they represent practical targets for interventions aimed at reducing dementia risk at the population level.”

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