Background The detrimental impact of social isolation has been reported for several individual outcomes, but less evidence has explored the association between isolation and multi-dimensional measures of healthy ageing. As part of the World Health Organisation’s framework for healthy ageing, intrinsic capacity (IC) is defined as an individual’s total physical and mental capacities. The use of IC as a measure of healthy ageing is increasing, but longitudinal evidence is still sparse. This study tested the association between social isolation and a novel measure of IC over four waves of the English Longitudinal Study of Ageing in 2,654 adults aged ≥60 years.

Methods An IC score was generated in wave 2 (baseline) and three follow-ups (waves 4, 6 and 8/9). Nine indicators were summed into a score (0–9) with higher scores indicating better IC. Indicators and their ‘pass’ cut-offs were: word recall (top two tertiles), orientation-in-time (all correct), self-report eyesight and hearing (good—excellent), walking speed (≥0.8m/s), grip strength (≥30kg men; ≥20kg women), BMI (≥18.5 and <30), CES-D (score <4), Satisfaction With Life Scale (score ≥20). An index of social isolation (0–7), with higher scores meaning greater isolation, was generated at baseline and each follow-up from seven indicators, each worth 1 point: living alone, less than monthly face-to-face or telephone contact with children/family/friends, not being a member of any organisations, not working, not volunteering. The complete-case sample was restricted to those with IC and isolation scores at baseline and no missing data on covariates. Sequential growth curve models included the predictors age and sex, isolation, and then covariate blocks of socioeconomic factors, health behaviours, health; a fully-adjusted model included all predictors and covariates.

Results In the unconditional model, average IC score at baseline was 7.06, decreasing 0.23 units over each follow-up to 6.38 at the final wave. In a model including isolation, age, and sex, higher isolation was associated with lower baseline IC (beta=-0.23, 95% CI=-0.28 — -0.18) but not associated with the rate of change of IC. This effect remained after adjusting for socioeconomic factors, health behaviours and self-rated health.

Conclusion These results suggest social isolation has a detrimental effect on IC level, but not on the rate of decline over time. However, this initial complete-case analysis should be expanded with imputation of missing data and more complex modelling of IC trajectories. Nevertheless, the study highlights the potential of this novel IC model to monitor IC over time and explore factors detrimental to healthy ageing.