Frailty increases with age and is associated with negative health outcomes as falls, hospitalization, and mortality. Socio-economic situation (SES) in childhood and adulthood are associated with frailty. It is unclear how the interaction of childhood hardship and adulthood SES effects frailty.

A register-based study using data from national registers and from the Lolland-Falster Health Study, involving individuals aged 50 and above. Frailty status was assessed using a modified version of Fried’s phenotype. Logistic regression models with multiple adjustments were used to analyze the odds of frailty. Causal interactions between economic hardship in adulthood, perception of childhood, self-reported stressful events in childhood, and self-reported educational level were assessed by estimating the relative excess risk due to interaction (RERI).

The study included 10,163 individuals. The percentage of individuals fulfilling 2–5 frailty criteria varied between 17 % in the 50–65 age group and 44.9 % in the 85+ age group. Women had a higher proportion of fulfilling 2–5 frailty criteria (21.5 %) compared to men (17.2 %). Socio-economic factors associated with frailty status included perception of childhood, stressful childhood events, educational attainment, and economic hardship in adulthood. A significant causal additive effect on the percentage of individuals fulfilling 2–5 frailty criteria was demonstrated for two composite outcomes: perception of childhood + educational attainment and stressful events in childhood + economic hardship in adulthood.

The study showed that joint exposure to adverse socio-economic factors in childhood and adulthood, potentiated the odds of frailty in older adults. Our findings corroborate the theory of cumulative dis/advantage.