Occupational physical and cognitive demands across adulthood and later-life risk of dementia

Abstract Background High levels of occupational physical activity (OPA) have been associated with higher dementia risk, whereas cognitively demanding work may delay the onset of dementia and mild cognitive impairment (MCI). We examined associations between trajectories of OPA and occupational cognitive demands at ages 30-65 with risk of dementia and MCI at age 70+. Methods We included 7005 participants (49.8% women, aged 69-104) from the Norwegian Trøndelag Health Study (HUNT4 70+). Group-based trajectory modelling identified trajectories of OPA and occupational cognitive demands using national registry data (1960-2014) including data from 305 unique occupations. Dementia and MCI were clinically assessed in 2017-2019. We applied multi-adjusted multinomial regression to estimate relative risk ratios (RRR) with 95% confidence intervals (CI) for dementia and MCI, using inverse probability weighting and multiple imputation to address non-participation and missing data. Results A stable high OPA trajectory (35%) was associated with higher risk of dementia (RRR 1.34, 1.04-1.73) and MCI (1.80, 1.54-2.11), whereas a stable intermediate OPA trajectory (25%) was linked to higher MCI risk (1.36, 1.15-1.61) compared to the stable low OPA trajectory (31%). Participants with a stable low occupational cognitive demands trajectory (20%) had higher risks of dementia (1.37, 1.01-1.86) and MCI (1.74, 1.41-2.14) compared to those with a stable high occupational cognitive demands trajectory (20%). Conclusions Long-term engagement in physically demanding or cognitively undemanding occupations was linked to elevated dementia and MCI risk. These findings highlight the need for preventive strategies targeting individuals in physically intensive jobs and jobs with limited cognitive stimuli. Further research is needed to identify which specific types of OPA are most detrimental, and which aspects of occupational cognitive demands are most beneficial, for preserving cognitive function in later life.