The socio-economic inequality in the accelerated biological ageing metrics and their associations with multimorbidity

Multimorbidity—the co-occurrence of two or more chronic conditions— is usually linked to poorer quality of life, disability, and even higher mortality. However, chronological age only reflects the number of years since birth and provides no information about the body. Epigenetic age is calculated age based on the expression of DNA, which can be influenced by many factors in one’s life, such as environment, stress, diet etc. Individuals with the same chronological age might have different epigenetic ages. Aim: This PhD will focus on Accelerated Ageing(AA), defined as the difference between the chronological age and epigenetic age, to investigate the association between AA and multimorbidity, and how SEP or health behaviours affect association. Method: In the UK Household Longitudinal Study (Understanding Society), there are seven epigenetic clocks: first-generation clocks: Hovarth, Hannum, Lin, Hovarth Skin&Blood and second-generation clocks:PhenoAge and third-generation: DunedinPoam and DunedinPace. Multimorbidity was constructed using the doctor-diagnosed diseases across 15 waves of follow-up. Logistic regression was used for the association between AA and prevalent multimorbidity. Cox models were used to assess the association between AA and the risk of incident multimorbidity. Findings: Overall, AA measured by second-generation epigenetic ageing clocks was associated with higher odds than the first-generation clocks,and effect sizes attenuated after adjustment for socioeconomic factors and health behaviours. A stronger association was observed among men and people in their midlife. In the longitudinal analysis, several epigenetic ageing measures showed positive associations with incident multimorbidity, with the largest estimates for DunedinPACE. Men showed a stronger association than women, and significant results were observed only in the younger population. These associations were attenuated after adjustment, and there was limited evidence of independent associations after further adjusting for the health behavioural factors.