Trajectories of Occupational Cognitive Demands and Risk of Mild Cognitive Impairment and Dementia in Later Life: The HUNT4 70+ Study.
Level 3 - non-randomized controlled study
Longitudinal cohort study with registry linkage
PubMed 38630959 · doi:10.1212/WNL.0000000000209353
What was done
The authors evaluated the association between midlife occupational cognitive demands (ages 30–65 years) and later-life clinical mild cognitive impairment (MCI) and dementia among 7,003 participants (aged 69–104 years, 49.8% women) in the Norwegian HUNT4 70+ Study (2017–2019). Occupational demand was assessed via the routine task intensity (RTI) index (lower RTI reflects greater cognitive demand) across 305 occupations. Group-based trajectory modeling classified participants into 4 RTI trajectories. Multinomial regression estimated relative risk ratios (RRRs), adjusting for demographics, income, and health/lifestyle factors measured during HUNT1–2 (1984–1997).
What was found
Participants fell into four RTI trajectory groups: low RTI (20.4%), intermediate-low (22.5%), intermediate-high (37.1%), and high RTI (19.9%). Compared with the low RTI group, participants in the high RTI group (least cognitively demanding) had elevated risks of MCI (RRR 1.74, 95% CI 1.41–2.14) and dementia (RRR 1.37, 95% CI 1.01–1.86) after adjusting for age, sex, and education. With further adjustment for income and baseline health/lifestyle factors, the association remained significant for MCI (RRR 1.66, 95% CI 1.35–2.06) but attenuated for dementia (RRR 1.31, 95% CI 0.96–1.78).
Why it matters
This study provides population-level longitudinal evidence that working in cognitively demanding jobs throughout midlife is associated with a lower risk of MCI and dementia in older age, consistent with the cognitive reserve hypothesis.
Limits
Occupational demands were inferred from job-title registries via standard indices rather than individual-level task measurements. Baseline early-life cognitive ability (prior to age 30) was not adjusted for, leaving open the possibility of confounding by baseline intelligence or education quality. The association with dementia did not retain statistical significance after full multivariable adjustment for income and health covariates.
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