METHODS: We harmonized longitudinal data of 11,988 participants from 10 cohorts in eight countries to examine the dose-response relationship between late-life physical activity and incident dementia among older adults.

RESULTS: Using no physical activity as a reference, dementia risk decreased with duration of physical activity up to 3.1 to 6.0 hours/week (hazard ratio [HR] 0.88, 95% confidence interval [CI] 0.67 to 1.15 for 0.1 to 3.0 hours/week; HR 0.68, 95% CI 0.52 to 0.89 for 3.1 to 6.0 hours/week), but plateaued with higher duration. For the amount of physical activity, a similar pattern of dose-response curve was observed, with an inflection point of 9.1 to 18.0 metabolic equivalent value (MET)-hours/week (HR 0.92, 95% CI 0.70 to 1.22 for 0.1 to 9.0 MET-hours/week; HR 0.70, 95% CI 0.53 to 0.93 for 9.1 to 18.0 MET-hours/week).

METHODS: Data were from population-based studies of aging and their Harmonized Cognitive Assessment Protocols (HCAPs) in the US, South Africa, India, and Mexico (N = 10,037; Age range: 50 to 105 years; 2016 to 2020). Main lifetime occupational skill was classified according to the International Standard Classification of Occupations. Weighted, adjusted regression models estimated pooled and country-specific associations between main lifetime occupational skill and later-life general cognitive function in men and women.

RESULTS: We observed positive gradients between occupational skill and later-life cognitive function for men and women in the US and Mexico, a positive gradient for women but not men in India, and no association for men or women in South Africa.

DISCUSSION: Main lifetime occupations may be a source of later-life cognitive reserve, with cross-national heterogeneity in this association.

METHODS: A total of 29,850 participants (58% women) from 21 cohorts across six continents were included in an individual participant data meta-analysis. Sex-specific hazard ratios (HRs), and women-to-men ratio of hazard ratios (RHRs) for associations between RFs and all-cause dementia were derived from mixed-effect Cox models.

RESULTS: Incident dementia occurred in 2089 (66% women) participants over 4.6 years (median). Women had higher dementia risk (HR, 1.12 [1.02, 1.23]) than men, particularly in low- and lower-middle-income economies. Associations between longer education and former alcohol use with dementia risk (RHR, 1.01 [1.00, 1.03] per year, and 0.55 [0.38, 0.79], respectively) were stronger for men than women; otherwise, there were no discernible sex differences in other RFs.

METHODS: We used individual participant data (N = 39271, Mage  = 70.67 (40-102), 58.86% female, Meducation  = 8.43 years, Mfollow-up  = 3.22 years) from 13 longitudinal ageing studies. A two-stage meta-analysis of Cox regression models examined the association between social connection markers with our primary outcomes.

RESULTS: We found associations between good social connections structure and quality and lower risk of incident mild cognitive impairment (MCI); between social structure and function and lower risk of incident dementia and mortality. Only in Asian cohorts, being married/in a relationship was associated with reduced risk of dementia, and having a confidante was associated with reduced risk of dementia and mortality.

DISCUSSION: Different aspects of social connections - structure, function, and quality - are associated with benefits for healthy aging internationally.