Multimorbidity: disease of society?
Authors: Alessandra Marengoni, Davide Liborio Vetrano
Journal: The Lancet Healthy Longevity (2021)

Socioeconomic inequalities are major health determinants, but could be leveraged more efficiently to promote health and wellbeing on a large scale. 30 years ago, in the Whitehall study of British civil servants, Marmot and colleagues1Marmot MG Smith GD Stansfeld S et al.Health inequalities among British civil servants: the Whitehall II study.Lancet. 1991; 337: 1387-1393Summary PubMed Scopus (2458) Google Scholar showed a clear gradient in various conditions, such as angina and chronic bronchitis, as well as several health risk behaviours, across different employment grades. An alternative way to look at the detrimental effect of socioeconomic deprivation on health, rather than looking at single diseases, is to measure multimorbidity—the co-occurrence of multiple chronic diseases in the same individual. Such a focus is particularly relevant considering the current demographic transition, in which the number and proportion of older adults is growing. The prevalence of multimorbidity increases with increasing age but is not exclusive to older people. On the contrary, when considering absolute numbers, younger adults contribute most to the global burden of multimorbidity, and the socioeconomic gradient might have the largest effect on multimorbidity occurrence in this age group.2Barnett K Mercer SW Norbury M Watt G Wyke S Guthrie B Epidemiology of multimorbidity and implications for health care, research, and medical education: a cross-sectional study.Lancet. 2012; 380: 37-43Summary Full Text Full Text PDF PubMed Scopus (3368) Google Scholar, 3Vetrano DL Calderón-Larrañaga A Marengoni A et al.An international perspective on chronic multimorbidity: approaching the elephant in the room.J Gerontol A Biol Sci Med Sci. 2018; 73: 1350-1356Crossref PubMed Scopus (85) Google Scholar In The Lancet Healthy Longevity, Anna Head and colleagues4Head A Fleming K Kypridemos C Schofield P Pearson-Stuttard J O'Flaherty M Inequalities in incident and prevalent multimorbidity in England, 2004–19: a population-based, descriptive study.Lancet Healthy Longev. 2021; (published online July 21.)https://doi.org/10.1016/S2666-7568(21)00146-XSummary Full Text Full Text PDF Scopus (10) Google Scholar characterise multimorbidity in adults in England from 2004–19 and explore how this varies by socioeconomic status using general practice records. Findings from this study can be summarised into two main points. First, a steady increase in multimorbidity prevalence was observed between 2004 and 2019, coupled with a substantial decrease in the median age of multimorbidity onset. Second, the association between socioeconomic inequalities and multimorbidity prevalence was amplified over the study period, particularly in middle-aged people (<65 years). A criticism of any study on multimorbidity is the method chosen to operationalise it. In the present study, Head and colleagues4Head A Fleming K Kypridemos C Schofield P Pearson-Stuttard J O'Flaherty M Inequalities in incident and prevalent multimorbidity in England, 2004–19: a population-based, descriptive study.Lancet Healthy Longev. 2021; (published online July 21.)https://doi.org/10.1016/S2666-7568(21)00146-XSummary Full Text Full Text PDF Scopus (10) Google Scholar define multimorbidity as two or more diseases, from a list of 211. This quantitative evaluation of multimorbidity has the advantage of conceptual simplicity, especially when a high number of diseases is evaluated. Furthermore, the contribution of any disease, including rarer diseases, is considered. However, this approach fails to differentiate people displaying different levels of morbidity, and scores equally those with two conditions and those with a much higher number of co-occurring diseases, with the consequence of an early saturation of the construct. Aware of this limitation, the authors also defined so-called complex multimorbidity, the presence of at least three diseases in three or more body systems. Still, this methodology fails to consider the potentially important relationships between diseases. Diseases tend to cluster together according to shared risk factors, treatments, and socioeconomic status.5Marengoni A Roso-Llorach A Vetrano DL et al.Patterns of multimorbidity in a population-based cohort of older people: sociodemographic, lifestyle, clinical, and functional differences.J Gerontol A Biol Sci Med Sci. 2020; 75: 798-805PubMed Google Scholar Tracing the secular trends of multimorbidity—defined as disease clusters—might be reasonable in studies evaluating inequalities, which could prompt the aggregation of specific diseases due to unhealthy lifestyles or poor environment. This approach might also overcome the problem of contribution of single conditions that might have been tested for or screened differently over time, or that underwent changes in reimbursement systems in primary care, to the overall multimorbidity prevalence. Despite these methodological issues, Head and colleagues'4Head A Fleming K Kypridemos C Schofield P Pearson-Stuttard J O'Flaherty M Inequalities in incident and prevalent multimorbidity in England, 2004–19: a population-based, descriptive study.Lancet Healthy Longev. 2021; (published online July 21.)https://doi.org/10.1016/S2666-7568(21)00146-XSummary Full Text Full Text PDF Scopus (10) Google Scholar findings are important as they show that the multimorbidity burden for the health-care system increased during the analysed time window. The reason for this could include a reduction in case fatality, driven by advancements in treatment and better secondary and tertiary prevention. A question arises about primary prevention, given that the median age of onset of multimorbidity is reducing over time, but the effect being driven by an increase in specific diagnoses cannot be ruled out. More striking is the widening of absolute socioeconomic inequalities in both basic and complex multimorbidity prevalence over the study period, which is in line with reports on widening of inequalities in health expectancy by social deprivation in England.6Bennett HQ Kingston A Spiers G et al.Healthy ageing for all? Comparisons of socioeconomic inequalities in health expectancies over two decades in the Cognitive Function and Ageing Studies I and II.Int J Epidemiol. 2021; (published online Jan 9.)https://doi.org/10.1093/ije/dyaa271Crossref Scopus (7) Google Scholar An important question is whether increasing inequalities account for widening of multimorbidity or if the association between socioeconomic status and multimorbidity changes over time. Another query concerns the model that best explains inequalities in health: social causation, which considers that socioeconomic position determines health during the life course, or health selection, which considers that social mobility depends on health status.7Hoffmann R Kröger H Geyer S Social causation versus health selection in the life course: does their relative importance differ by dimension of SES?.Soc Indic Res. 2019; 141: 1341-1367Crossref Scopus (23) Google Scholar Previous findings appear to endorse the social causation model. In the ATHLOS consortium, in which eight longitudinal cohorts from Australia, USA, Japan, South Korea, Mexico, and Europe were harmonised, the disadvantage due to low education and wealth caused deterioration in health in early life stages, leading to persistent differences throughout older age,8Wu YT Daskalopoulou C Muniz Terrera G et al.Education and wealth inequalities in healthy ageing in eight harmonised cohorts in the ATHLOS consortium: a population-based study.Lancet Public Health. 2020; 5: e386-e394Summary Full Text Full Text PDF PubMed Scopus (31) Google Scholar suggesting that adopting a life-course approach to investigate mechanisms leading to health inequalities might be appropriate.9Marengoni A Calderon-Larrañaga A Health inequalities in ageing: towards a multidimensional lifecourse approach.Lancet Public Health. 2020; 5: e364-e365Summary Full Text Full Text PDF PubMed Scopus (4) Google Scholar To date, public policies addressing socioeconomic disparities have been insufficient. A clear demonstration of this is the differing effects of the COVID-19 pandemic across social strata of the population. It has been hypothesised that, in England, the growing inequality during recent years, along with an increasing prevalence of chronic conditions and multimorbidity increasing the case fatality ratio of COVID-19, could partly explain one of the worst infection and mortality rates in Europe.10Marmot M Allen J Goldblatt P Herd E Morrison J Build back fairer: the COVID-19 Marmot review. The pandemic, socioeconomic, and health inequalities in England. Institute of Health Equity, London2020Google Scholar Furthermore, inequalities in health will probably increase in the near future as a consequence of the pandemic (eg, students from poorer households have been less able to access online learning and unemployment will probably increase). Thus, substantial support in low-income regions and strata of society is needed to break the chain of inequality, and adopting a long-life multidimensional approach to population health is key. We declare no competing interests. Inequalities in incident and prevalent multimorbidity in England, 2004–19: a population-based, descriptive studyThe burden of multimorbidity in England has increased substantially over the past 16 years with persistent inequalities, which are worse in working-age adults and for complex multimorbidity. Prevention efforts to reduce the onset and slow the progression of multimorbidity are essential to reduce the increasing impact on patients and health systems alike. Full-Text PDF Open Access