A new study published in JAMA Network Open reports that people who stay physically active in midlife and late life may cut their risk of dementia by as much as 41% to 45%. The strongest protection came from those in the highest activity group, and similar results were seen for Alzheimer’s disease specifically.
Why Researchers Looked at Timing of Exercise
Dementia remains a major public-health challenge. Current Alzheimer’s treatments offer only limited benefits and may cause side effects, so prevention is a priority. Many studies suggest that lifestyle changes, including regular exercise, could prevent a significant number of dementia cases.
Although past research shows that physical activity in midlife or later life improves brain health, it has been less clear whether activity earlier in adulthood offers the same long-term protection. Early-life studies often rely on memory-based reports, which can be inaccurate, especially in older adults with cognitive decline.
To better understand this timing question, researchers used long-term data from the Framingham Heart Study, which began in the 1970s. They analyzed how exercise during early adulthood, midlife, and late life related to dementia risk decades later.
How the Study Was Conducted
Participants were included if they did not have dementia and had physical-activity data at one of three life stages:
- Early adulthood: ages 26–44
- Midlife: ages 45–64
- Late life: ages 65–88
The study analyzed 1,526 early-adult participants, 1,943 midlife participants, and 885 late-life participants. All gave informed consent.
Researchers measured physical activity using the Physical Activity Index, which scores time spent sleeping, sitting, and doing light, moderate, or heavy activity. Higher scores indicate more total activity. These scores were divided into age-specific quintiles.
Participants were followed until they developed dementia, died, or reached the end of 2023. Dementia diagnoses were made using standard medical criteria.
Statistical models adjusted for age, sex, education, smoking, BMI, hypertension, diabetes, cholesterol, and APOE ε4, a major genetic risk factor for Alzheimer’s.
Who Developed Dementia
During follow-up, 567 people developed dementia:
- 4% of the early-adult group
- 14% of the midlife group
- 26% of the late-life group
Individuals with the lowest physical-activity levels had higher mortality in every age group.
Midlife and Late-Life Exercise Show Strongest Protection
After adjusting for health and demographic factors, only midlife and late-life exercise were linked to a significantly lower dementia risk.
In both stages, people in the highest activity groups (Q4 and Q5) had about 40% lower risk than those in the lowest group.
Early-adult activity showed no clear association, likely because fewer people developed dementia at younger ages.
Midlife benefits were strongest for moderate and heavy activity, while late-life activity was helpful at all intensity levels.
Genetics Influence the Effects of Physical Activity
The APOE ε4 gene changed how physical activity affected risk:
- In midlife, higher activity strongly reduced dementia risk for non-carriers.
- In late life, activity lowered risk for both carriers and non-carriers.
- For ε4 carriers, only the highest late-life activity level clearly lowered risk.
Patterns were similar for Alzheimer’s disease, although the association among ε4 carriers did not reach statistical significance.
Strengths and Limitations
The study benefits from its long follow-up, detailed dementia assessments, and extensive health data. However, several factors may limit its generalizability:
- Participants were mostly of European ancestry.
- Early-adult dementia cases were few.
- Physical-activity levels were self-reported and collected only once per life stage.
- Early-life activity could not be assessed.
- Some misclassification or survival bias is possible.
Conclusion
The findings identify midlife and late life as the most important periods during which physical activity can lower the risk of dementia, including Alzheimer’s disease. The results support long-term public-health efforts to promote regular exercise, especially beginning in midlife, to help preserve cognitive health.
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