Birth size modifies longitudinal associations between midlife educational level and physical function at late-life...

Physical function is an important domain of healthy ageing and previous studies have suggested socioeconomic status, including education to be influential. Also, lifestyle factors such as physical activity can play a crucial role in maintaining physical function. Furthermore, birth size as an indicator of nutritional status during gestation can add insight into the interplay between factors that influence physical functioning. Thus, examining healthy ageing from a life course perspective can broaden our scope for possible preventive measures for maintaining independence and quality of life at late-life. Our objective was to investigate the longitudinal association between midlife education and late-life physical function, over the mean time-period of 25 years, and to investigate whether birth size modifies the association.

Participants were 1604 men and women from the Age Gene/Environment Susceptibility (AGES) - Reykjavik Study who had measures from birth, midlife and late-life. Multivariate linear regression included gait speed (GS) and timed up and go test (TUG) at late-life as outcomes and midlife educational level as exposure. To examine effect modification, data was stratified by birth size as ponderal index (PI) in three groups.

Participants with primary education had slower GS of 0.05 m/s (p < 0.001) and longer TUG time of 0.66 s (p = 0.006) compared to college/university (reference). Birth size modified the association, with the low PI group having a slower GS of 0.1 m/s (p < 0.001) and taking 1.35s longer to complete TUG between educational groups (primary education vs. reference). There was no association between GS nor TUG with education in the high PI group.

Our results imply that for those born small, having lower educational level is associated with having worse physical function at late-life, partly through less physical activity throughout the life-course.