Biological ageing and 12-year trajectories of subjective functional decline across the entire adult age span: evidence from the UK Household Longitudinal Study

Ageing begins early in life, but most ageing-related research, interventions and public health policy focus on later life. Identifying early biological ageing processes linked to functional decline could inform preventive strategies across the life course. We examined whether molecular and physiological biomarkers of ageing predict longitudinal changes in subjective functioning. We used data from the nationally representative study, the UK Household Longitudinal Study. Biological ageing was measured in 2010-2012 for people aged 16 or older (up to 13,231 participants), using Biological Health Score (BHS), a physiological composite biological ageing measure, and also using DNA methylation algorithms. Subjective functioning was assessed by physical component score (PCS) and mental component score of Short Form 12-item Survey and self-rated health. Growth curve models estimated 12-year trajectories of functioning in relation to baseline biological ageing, controlling for sociodemographic factors. Additional analyses stratified models by sex and age group. Accelerated biological ageing is associated with worse functioning, and accelerated biological ageing (BHS, PhenoAge and DunedinPACE DNA methylation algorithms) at baseline predicts faster (or steeper) subsequent functional decline. For example, higher BHS was associated with steeper declines in PCS (year * BHS interaction term, coefficient = -0.014, 95% confidence interval = -0.024 to -0.005). Associations varied by sex and age group, with midlife adults showing largest effects, suggesting a potential key window for preventive action. Subjective measures captured ageing dynamics across the full adult age span, and blood-based biomarkers provided early risk signals. Integrating subjective functioning measures into routine health surveys, clinical screening, or workplace health checks could help identify at-risk adults earlier. Molecular and physiological ageing measures identify populations at risk of early decline before disability or disease onset. Implementing multidimensional ageing assessments in young and mid-adulthood could inform timely interventions, reduce disability and disease burden across the life course, and promote healthy ageing.