Minimum physical activities protective against Alzheimer's disease in late life: a systematic review.

Context: Previous studies indicate an inverse relationship between physical activity (PA) and the risk of Alzheimer's disease (AD). Although they highlighted the health benefits of PA, the specific effects of PA in late life remain unclear, and intense PA may be challenging for older adults. Moreover, there is significant variation in how PA is assessed, including the timing and types of activities considered.

Objectives: This review aimed to evaluate existing literature to determine the effects of PA with an emphasis on late-life PA and the minimum levels of PA for older adults.

Methods: We conducted a systematic review via the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) protocol utilizing the MEDLINE and Cumulative Index to Nursing and Allied Health Literature (CINAHL) databases, last assessed in July 2023. Studies that met the inclusion criteria were prospective cohort or interventional studies, that are written in English, and that measured PA in a cohort who did not have dementia, AD, or cognitive decline at baseline. Retrospective cohort, cross-sectional, case reports, and studies not meeting the inclusion criteria were excluded. Each study was evaluated in seven domains of bias utilizing the Risk Of Bias In Non-randomized Studies of Exposures (ROBINS-E) tool.

Results: Out of 2,322 studies screened, 17 met the inclusion criteria, including six new studies not included in the previous systematic review. This resulted in 206,463 participants from North America (United States and Canada) and Europe (Denmark, Finland, Italy, Sweden, and the United Kingdom). Our method effectively reduced the number of duplicated studies during screenings, resulting in 92 duplications compared to 3,580 in the previous review. The risk of bias assessment in the quality of evidence was "low risk" in 13 studies and "some concerns" in four studies. Four studies assessed PA at midlife (average age, 49 years; average follow-up time, 29.2 years), 11 studies assessed PA in late life (average age, 75.9 years; average follow-up time, 5.9 years), and two assessed PA in adulthood without specification. For studies that assessed PA at midlife, 2 out of 4 (50 %) had statistically significant findings (p<0.05) for studies that assessed PA during late life, 8 out of 11 (75 %) had significant findings (p<0.05), and 2 out of 2 (100 %) of unspecified timing had significant findings (p<0.05). Our review indicated that engaging in PA at least three times per week, for at least 15 min per session, was judged to be the minimum requirement tested for protective effects against AD in late life. Potential biological mechanisms were also discussed.

Conclusions: Our current review supports existing evidence that PA provides significant protection against the development of AD and found that the requirement of PA may be less than the current guidelines for sufficient and meaningful protection in late life. Excitingly, any form of PA tested can be protective against the development of AD, including household activities, suggesting that a wider variety of PA can be more appropriate for late life. More standardized and detailed studies are needed to update the benefits of PA, particularly in the areas of occupational, household/transportation, and age-group activities. Further research is needed to determine the optimal PA thresholds in these groups.