Data from millions of people reveal that everyday habits, like how much you move, sit, and sleep, could play a crucial role in shaping long-term brain health and dementia risk.
Study: The Relationships between physical activity, sedentary behaviour, sleep, and dementia: A systematic review and meta-analysis of cohort studies. Image credit: TB studio/Shutterstock.com
A large new study in PLOS One suggests that physical activity, adequate sleep, and less sedentary time may be associated with a lower risk of dementia.
Dementia is a leading cause of death among older people, and affects about 55 million people the world over. By 2050, the number of cases may triple, most cases occurring in low-resource settings. The high societal, personal, and economic costs of managing dementia make it urgent to identify preventable conditions that increase the risk.
Modifiable risk factors
Physical activity has long been linked to better cognitive function, although its direct relationship with dementia risk remains less clearly defined. Several biological pathways may help explain this association. For example, regular physical activity is associated with reduced chronic inflammation and improved cardiovascular health, both of which are important for maintaining cognitive function.
In contrast, sedentary behavior, defined as waking time spent in low-energy activities such as sitting or reclining, is associated with increased cardiovascular risk. Prolonged sitting has been linked to metabolic and inflammatory changes that may contribute to neurodegenerative disease. The 2024 Lancet Commission estimated that around 2 % of new dementia cases could be attributed to low levels of physical activity in midlife.
Sleep also appears to play a key role. Both insufficient and excessive sleep have been associated with higher risks of mortality and dementia. While advancing age remains the strongest risk factor for dementia, evidence suggests that lifestyle modifications, including improvements in physical activity, sleep, and sedentary behavior, could delay or potentially prevent up to 45 % of cases among at-risk populations. However, despite growing evidence linking these behaviors to dementia risk, high-quality data to inform clear, evidence-based lifestyle guidelines remain limited.
To address this gap, the current study synthesized data from multiple long-term prospective cohort studies through a systematic review and meta-analysis. Notably, many of the included studies were assessed as having a risk of bias, particularly due to confounding factors, which should be considered when interpreting the findings.
Physical activity
There were 49 articles dealing with physical activity. About half of the studies reported statistically significant reductions in dementia risk, and pooled results showed a 25 % lower risk among physically active adults aged 50 and older.
Increased physical activity improves cerebral blood flow and antioxidant capacity. It also stimulates the production of neuroprotective molecules, such as brain-derived neurotrophic factor (BDNF), and improves neurotransmitter function. These biological mechanisms might contribute to the lower dementia risk, but were not directly demonstrated in these studies.
Sleep
About half of the 17 included studies found that both short and long sleep (<7 and >8 hours per night, respectively) were linked to a higher risk of dementia, by 18 % and 28 %, respectively.
The glymphatic system clears waste products from brain cells and increases the flow of cerebrospinal fluid (CSF) through the brain. Too little sleep, especially coupled with more sedentary time or low physical activity, may reduce the activation of this system. This may be linked to processes associated with brain atrophy and accelerated brain aging.
Long sleep may predispose to or worsen underlying chronic conditions, trigger systemic inflammation, or be a marker of early neurodegenerative disease.
Sedentary behavior
The evidence for sedentary behavior was more limited. Only three studies were included, which showed that dementia risk was 27 % higher among those with 8 or more hours of sitting time per day. Conversely, it was lower among those who sat less than 8 hours a day.
Strengths and limitations
Clinical diagnoses of dementia were based on valid and reliable criteria. Large sample sizes were obtained from community-based cohorts with long follow-up. This increased the power to detect the outcomes. Diverse populations allowed for greater generalizability of the findings.
Study limitations include heterogeneity across studies, the potential for reverse causation in findings based on short-term studies, self-reported activity, sedentary behaviors, and sleep durations, and the assessment that moderate to serious risk of bias existed across studies. Notably, heterogeneity was substantial in several analyses, particularly for physical activity, which may affect the certainty of the findings.
Implications and future directions
Participants who engage in regular physical activity, spend less time sedentary, and maintain 7–8 hours of sleep each night may be less likely to develop dementia, although these findings reflect associations rather than direct cause-and-effect relationships and are consistent with earlier research. This meta-analysis builds on previous evidence by drawing on larger, more diverse populations from recent studies, with longer follow-up periods, and a focus on adults primarily aged 50 and older.
Lifestyle behaviors such as physical activity, sleep, and sedentary time are widely targeted in public health interventions and may collectively influence dementia risk. Importantly, these factors do not operate in isolation; they are closely interconnected and can interact with coexisting health conditions, making their combined effects more complex to interpret.
At the same time, the long preclinical phase of dementia, where changes may begin up to a decade before diagnosis, makes it difficult to establish clear links between modifiable risk factors and disease progression. This highlights the need for further research, particularly in middle-aged populations, using long-term follow-up to better understand how these behaviors and their changes over time interact to influence dementia risk.
Stronger evidence from such studies will be essential for developing robust, evidence-based guidelines to support healthier daily routines from midlife onwards. These could include community-based initiatives, such as walking or exercise groups, alongside broader public health strategies, such as improving access to safe green spaces and implementing workplace policies that encourage regular movement rather than prolonged sitting.
Together, these findings suggest that healthy daily habits, physical activity, less time sitting, and proper sleep could be associated with a reduced risk of dementia over the long term, although further research is needed to establish causal relationships.
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