A large UK Biobank study suggests that how adults accumulate daily movement, not only how much they do, may be relevant to future brain and mental health.
Study: Associations of physical activity bout duration and fragmentation with future dementia, depression, and anxiety: a multi-modal UK Biobank study. Image Credit: ahmetmapush / Shutterstock
Longer bouts of moderate-to-vigorous physical activity and less fragmented activity were each associated with a significantly lower risk of future inpatient diagnoses of dementia, depression, and anxiety, reported by a multimodal UK Biobank study published in the journal Translational Psychiatry.
Background
Physical activity is a healthy lifestyle behavior that helps improve both physical and mental well-being. Studies have linked greater physical activity to a lower risk of dementia, depression, and anxiety. The World Health Organization’s (WHO) physical activity guidelines recommend 150 to 300 minutes of moderate-intensity activity, 75 to 150 minutes of vigorous-intensity activity, or an equivalent combination per week.
These guidelines, however, focus primarily on total physical activity volume and provide limited insight into physical activity patterns. Identifying physical activity patterns that can provide the greatest physical and mental health benefits is therefore important for informing current guidelines.
A physical activity bout refers to a single event of specific-intensity physical activity performed for a specific duration, such as a 20-minute brisk walk. In 2020, the WHO withdrew its previous recommendation that moderate-to-vigorous activity should be performed in bouts lasting more than 10 minutes. Instead, the organization emphasized that all activity counts and that some activity is better than none. However, recent evidence has raised debate over whether prolonged physical activity provides greater health benefits than short bouts.
To provide meaningful insight into the ongoing debate, researchers at the City University of Hong Kong, China, assessed and compared the usefulness of physical activity bout duration and fragmentation in associations with the future risk of dementia, depression, and anxiety.
The researchers analyzed accelerometer-measured data on the longest daily active-intensity bout duration, moderate-to-vigorous physical activity bout duration, and activity fragmentation collected from 66,483 UK Biobank participants. Activity fragmentation measured how frequently an active minute was followed by sedentary time, with higher fragmentation indicating shorter, more intermittent activity patterns. The associations of these parameters with future inpatient diagnoses of dementia, depression, and anxiety were assessed after adjustment for potential confounding factors, including total physical activity.
Key Findings
The study analysis revealed that longer active-intensity bouts were associated with a lower risk of subsequent dementia and anxiety, whereas longer moderate-to-vigorous physical activity bouts and less fragmented activity patterns were associated with a lower risk of all three outcomes, irrespective of the total daily physical activity duration.
Compared with the shortest observed active bouts, which lasted two minutes, bouts lasting 47 minutes were associated with the lowest observed risk of dementia.
Compared with participants who recorded no moderate-to-vigorous physical activity, bouts lasting 13 minutes were associated with the lowest observed risk of dementia, while bouts lasting 36 minutes were associated with the lowest observed risk of depression and anxiety.
Compared with the highest observed activity fragmentation, the lowest observed fragmentation was associated with an 82%, 57%, and 52% lower risk of dementia, depression, and anxiety, respectively.
The analysis of neuroimaging data from a subgroup of 13,108 participants revealed that prolonged moderate-to-vigorous physical activity bouts and lower fragmentation were associated with greater left hippocampal volume and lower white matter hyperintensity volume. Longer moderate-to-vigorous physical activity (MVPA) bouts were also associated with greater right hippocampal volume, while lower fragmentation was associated with greater total brain volume. These cross-sectional analyses cannot determine whether activity patterns caused these structural differences.
Among participants carrying the apolipoprotein E ε4 (APOE4) allele, which is associated with increased dementia risk, dementia risk progressively decreased as activity fragmentation decreased. This suggests that fragmented activity patterns may serve as a novel target for reducing dementia risk among individuals who are genetically predisposed. However, this association does not establish that reducing fragmentation will reduce dementia risk.
Study Significance
The study reveals that prolonged moderate-to-vigorous physical activity with less activity fragmentation is associated with a significantly lower subsequent risk of dementia, depression, and anxiety.
Given the findings, the researchers hypothesized that prolonged physical activity may be more effective than fragmented activity in improving cardiorespiratory fitness and reducing neuroinflammation, which in turn may reduce dementia risk. For depression and anxiety, they highlighted the need for more evidence to gain insight into possible biological mechanisms.
Notably, the study found that prolonged and less fragmented physical activity was associated with more favorable brain structural measures than highly fragmented activity. Future research using longitudinal study designs is needed to determine the causal nature of the associations observed between physical activity patterns and brain structural changes.
Existing evidence on non-biological mechanisms indicates that prolonged high-intensity physical activity may support mental health through improved self-efficacy, resilience, and self-esteem. Moreover, prolonged aerobic activity has been found to improve mental health through socialization.
Another notable finding is the influence of APOE4 genotype on the associations between activity fragmentation and dementia risk. Given the findings, the researchers suggest that APOE4 carriers may reduce their activity fragmentation as much as possible to significantly reduce the risk of dementia. However, the authors note that further research is needed to assess whether activity fragmentation can be feasibly targeted as an intervention.
Given the overall study findings, the researchers suggest that middle-aged and older adults should be encouraged to undertake daily bouts of moderate-to-vigorous physical activity lasting 36 minutes. This corresponds to more than 250 minutes of moderate-to-vigorous physical activity per week, satisfying the WHO’s physical activity guidelines. This is an author-proposed public-health implication rather than a recommendation established by causal evidence.
Active-intensity bouts may serve as an alternative strategy for individuals who are unable to perform moderate-to-vigorous physical activity. However, they may require a greater time commitment to achieve beneficial dementia outcomes and were not significantly associated with a lower risk of depression.
The study also has limitations. Although the researchers excluded diagnoses occurring within the first two years and adjusted for baseline cognition and mental health measures, preclinical disease and reverse causation cannot be ruled out. In addition, the largely White UK Biobank cohort may limit the generalizability of the findings, and accelerometer thresholds may not capture all forms of activity, including strength training. As an observational study, it cannot establish cause and effect.
