Effects of self-rated mental and physical work demands on cognition are dependent in a cross-sectional sample of the Health and Retirement Study

Objective: This study assessed whether self-rated physical and mental work demands were associated with cognition among older working adults and whether their effects were dependent.

Methods: Our cross-sectional sample consisted of 6,377 working older adults uisng the Health and Retirement Study in 2004. Self-rated work demands were summarized from four questions about frequency of mental or physical demands in the respondent's current job. Cognition was assessed using a subset of the Telephone Interview for Cognitive Status. We used multivariable linear regression to test for associations and additive interaction between physical and mental work demands and cognition, adjusted for age, sex, race, education, and practice effect.

Results: Independently, higher physical work demands were associated (P<0.001) with poorer cognition and higher mental work demands were associated (P<0.001) with better cognition. The effect of one work demand measure became more negative as level of the other increased (B for interaction = -0.23, 95% CI: -0.43, -0.03). A one-point increase in mental work demands was associated with 0.79 (95% CI: 0.51, 1.08) points higher cognition score when physical work demands were lowest, but was not associated with cognition when physical work demands were highest (0.11, 95% CI: -0.26, 0.48). The highest predicted cognition score was for the highest mental and lowest physical work demands. Results were robust to additional adjustment for health and behavior covariates.

Conclusions: The associations of self-rated mental and physical work demands on cognition are dependent. Future studies should strongly consider examining interactions to capture the range of work demand effects.