School education, physical performance in late midlife and allostatic load: a retrospective cohort study

BACKGROUND: The mechanisms underlying the social gradient in physical functioning are not fully understood. Cumulative physiological stress may be a pathway. The present study aimed to investigate the association between highest attained school education and physical performance in late midlife, and to determine to what extent cumulative physiological stress mediated these associations.

METHODS: The study is based on data from the Copenhagen Aging and Midlife Biobank (CAMB; n=5467 participants, aged 48-62 years, 31.5% women). School education was measured as highest examination passed in primary or secondary school (3 categories). Cumulative stress was operationalised as allostatic load (AL), and measured as the number of biological parameters (out of 14) in which participants scored in the poorest quartile. Physical performance included dynamic muscle performance (chair rise ability, postural balance, sagittal flexibility) and muscle strength (jump height, trunk extension and flexion, and handgrip strength).

RESULTS: Among women, higher school education was associated with better performance in all physical performance tests. Among men, higher school education was associated with better performance only in chair rise and jump height. AL partially mediated the association between school education and physical performance, and accounted only for 2-30% of the total effect among women. Similar results were observed among men for chair rise and jump height.

CONCLUSIONS: These results might indicate that AL plays a minor role in the association between school education and late midlife dynamic muscle performance in both men and women, and in muscle strength among women.