Abstract
This thesis, as part of the larger Ageing Trajectories of Health: Longitudinal Opportunities and Synergies (ATHLOS) project, examined the patterns and risk factors of multimorbidity (the coexistence or two or more chronic illnesses in the same individual), as well as its relationship with mortality and healthy ageing (the process of developing and maintaining the functional ability that enables wellbeing in older age) in older adults. A key line of enquiry that this thesis pursues was exploring the heterogeneity of multimorbidity and healthy ageing, and the multifaceted association between these two concepts. This was carried out in several stages.The first line of investigation was the heterogeneity of multimorbidity in its operationalisation. This was described and summarised in a systematic review and meta-analysis. Wide variations in the prevalence of multimorbidity was found in 70 observational studies in community settings, ranging from 3.5% to 70% in high income countries (HICs), and from 1% to 90% in lower-and-middle-income countries (LMICs). Results from the meta-analysis showed that one third of the world’s population had multimorbidity. Multimorbidity prevalence was higher in HICs compared to LMICs (37% vs 29% respectively).
The second line of investigation was the heterogeneity of multimorbidity patterns (i.e. clusters of diseases). Using latent class analysis (LCA) based on data from 26 chronic conditions in the English Longitudinal Study of Ageing (ELSA), three patterns of multimorbidity were identified: 1) the cardiorespiratory/arthritis/cataracts group, 2) the metabolic group and 3) the relatively healthy group. The complexity level of multimorbidity was also revealed through this analysis, where the most complex multimorbidity pattern was found to be the cardiorespiratory/arthritis/cataracts group. The associations between these multimorbidity patterns and sociodemographic and lifestyle risk factors were also examined. Age, sex, wealth, smoking and physical activity were found to be associated with the most complex multimorbidity group. This supports the hypothesis that discordant multimorbidity where diseases with different aetiology and treatments cluster together could be attributable to upstream health risk factors.
The third line of investigation was the heterogeneity of the associations between multimorbidity patterns and health outcomes such as mortality and healthy ageing. Multimorbidity is often associated with poorer health outcomes. However, in this thesis it was found that those with multimorbidity could still achieve a relatively high level of healthy ageing, despite a negative association between the two. Only people belonging to the cardiorespiratory/arthritis/cataract group had higher risks of mortality during a 10-year follow up period. The association between multimorbidity and mortality did not differ when considering levels of healthy ageing. Nonetheless, healthy ageing seemed to have a mediating effect on the multimorbidity-mortality relationship. This supports the hypothesis that healthy ageing lies on the causal pathway between multimorbidity and mortality.
The fourth line of investigation was the heterogeneity of healthy ageing trajectories over the life course. In this line of enquiry, the relationship between multimorbidity and healthy ageing was explored further, in which the patterns of healthy ageing trajectories among 130880 participants from eight ATHLOS cohorts were identified and the impact of multimorbidity on the projection of healthy ageing trajectories was examined. Three patterns of healthy ageing trajectories were identified using the growth mixture modelling approach: 1) the ‘high stable’ group, which displayed a high level of healthy ageing at baseline and a slow decline over time, 2) a ‘low stable’ group, which showed a low level of healthy ageing at baseline and a slow decline over the follow-up period, and 3) a ‘rapid decline’ group, which presented a high level of healthy ageing at baseline but a steep downward slope over 11 waves. The presence of multimorbidity significantly increased the likelihood of an individual being in the ‘rapid decline’ or the ‘low stable’ groups.
In conclusion, this thesis illustrated the heterogeneity of multimorbidity and healthy ageing. It reiterated that multimorbidity is not synonymous with ill health. A person-centred integrated care model thus should be implemented to cater for the heterogeneous needs of people with multimorbidity.
| Date of Award | 1 Dec 0202 |
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| Original language | English |
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| Supervisor | Matthew Prina (Supervisor) & Silia Vitoratou (Supervisor) |