Is multimorbidity a useful concept for public health?
Authors: Martin C Gulliford, Judith M Green
Journal: The Lancet Public Health (2024)

The UK and its peers face enormous population health challenges and widening health inequalities, with growing impacts on the workforce and older populations. The concept of multimorbidity has come to the fore as a focus for addressing these challenges.1Lynch R Hanckel B Green J The (failed) promise of multimorbidity: chronicity, biomedical categories, and public health.Crit Public Health. 2021; 32: 450-461Crossref Scopus (2) Google Scholar, 2Langenberg C Hingorani AD Whitty CJM Biological and functional multimorbidity-from mechanisms to management.Nat Med. 2023; 29: 1649-1657Crossref Scopus (2) Google Scholar In this issue of The Lancet Public Health, Anna Head and colleagues3Head A Birkett M Fleming K Kypridemos C O'Flaherty M Socioeconomic inequalities in accumulation of multimorbidity in England from 2019 to 2049: a microsimulation projection study.Lancet Public Health. 2024; 9: e231-e239Summary Full Text Full Text PDF Google Scholar estimate trends in the prevalence of multimorbidity in England over the next three decades; they find that by 2049, 72% of adults aged 30–90 years could have multimorbidity, with disproportionate increases in multimorbidity in deprived populations. The study finds that a person aged 30 years is expected to live 12·2 years without multimorbidity in the most deprived quintile and 15·2 years in the least deprived. Despite this burden, the multimorbidity concept has important limitations as a metric for public health research and policy. We reflect on these limitations and discuss the usefulness of the concept in public health. Multimorbidity does not have a standard definition.4Ho IS Azcoaga-Lorenzo A Akbari A et al.Examining variation in the measurement of multimorbidity in research: a systematic review of 566 studies.Lancet Public Health. 2021; 6: e587-e597Summary Full Text Full Text PDF PubMed Scopus (81) Google Scholar Multimorbidity is typically said to exist when a person has two or more from a selected list of long-term conditions; however, some researchers call for all conditions, whatever their chronicity, to be included.2Langenberg C Hingorani AD Whitty CJM Biological and functional multimorbidity-from mechanisms to management.Nat Med. 2023; 29: 1649-1657Crossref Scopus (2) Google Scholar No standard list of conditions exists, and attempts to develop one have been guided by professional opinion rather than internationally recognised disease classifications.5Ho ISS Azcoaga-Lorenzo A Akbari A et al.Measuring multimorbidity in research: Delphi consensus study.BMJ Med. 2022; 1e000247 Crossref PubMed Google Scholar The term condition includes diverse categories, including diseases, risk factors (eg, obesity and hypertension), symptoms (eg, chronic pain), and impairments (eg, vision and hearing loss).5Ho ISS Azcoaga-Lorenzo A Akbari A et al.Measuring multimorbidity in research: Delphi consensus study.BMJ Med. 2022; 1e000247 Crossref PubMed Google Scholar The multiplicity of conditions cannot be equated with severity of illness; a single condition can sometimes cause more severe illness than multiple diagnoses. Furthermore, long-term conditions can relapse or remit. Assessment of resolution can make a substantial difference to multimorbidity prevalence estimates,6Ledwaba-Chapman L Bisquera A Gulliford M et al.Applying resolved and remission codes reduced prevalence of multimorbidity in an urban multi-ethnic population.J Clin Epidemiol. 2021; 140: 135-148Summary Full Text Full Text PDF PubMed Scopus (4) Google Scholar but resolution is not often evaluated. Multimorbidity research has been driven by the increasing availability of electronic health records for population health research. Health records are rich in medical diagnoses, and it is not surprising that most patients' longitudinal records can be associated with multiple diagnoses by the time older ages are reached. Health records do not currently include linked information concerning exposures to health determinants or risk factors over the life course, nor data for patient health outcomes, which are required for research into the causes and effects of multimorbidity. Single causes can have multiple effects, and individual risk factors such as smoking or obesity, or single-gene disorders such as sickle cell disease, could initiate pathophysiological processes that cause disease in multiple organs. A single syndrome might be rebranded as multimorbidity, but the value of so doing is not clear. Multimorbidity research increasingly uses data-driven approaches to identify clusters of diseases,7Ng SK Tawiah R Sawyer M Scuffham P Patterns of multimorbid health conditions: a systematic review of analytical methods and comparison analysis.Int J Epidemiol. 2018; 47: 1687-1704Crossref PubMed Scopus (71) Google Scholar but these approaches might not permit causal inferences.8Ramspek CL Steyerberg EW Riley RD et al.Prediction or causality? A scoping review of their conflation within current observational research.Eur J Epidemiol. 2021; 36: 889-898Crossref PubMed Scopus (29) Google Scholar Meanwhile, existing knowledge concerning well evidenced causal pathways linking, for example, poor diet and sedentary lifestyles with obesity and obesity-related morbidity, has not been sufficiently leveraged in health policy. Attention on multimorbidity could intensify a downstream focus on clinical risk factors and diseases. Counting clinically diagnosed diseases orients towards long-term conditions management, often framed in terms of secondary prevention. The multimorbidity concept has value in showing that management must be organised across specialties, requiring generalists in primary and older adult care.1Lynch R Hanckel B Green J The (failed) promise of multimorbidity: chronicity, biomedical categories, and public health.Crit Public Health. 2021; 32: 450-461Crossref Scopus (2) Google Scholar However, health-care settings do not generally provide the context for effective population-wide primary prevention strategies,9Alageel S Gulliford MC McDermott L Wright AJ Multiple health behaviour change interventions for primary prevention of cardiovascular disease in primary care: systematic review and meta-analysis.BMJ Open. 2017; 7e015375 Crossref Scopus (39) Google Scholar nor action on health inequalities. Individual-level risks, including blood pressure and smoking status, represent complex relational processes driven by social and environmental determinants of health and the eroding effect of social inequality.10Brunner EJ Marmot MG Nanchahal K et al.Social inequality in coronary risk: central obesity and the metabolic syndrome. Evidence from the Whitehall II study.Diabetologia. 1997; 40: 1341-1349Crossref PubMed Scopus (376) Google Scholar Societal actions are needed to address these risks. Multimorbidity research is at a descriptive stage, focusing on the prevalence and burden of disease. Questions of how affected individuals and populations can be supported remain to be addressed. Need is usually defined as the capacity to benefit, and this requires evidence for effective intervention, in addition to evidence of disease burden. To date, only a small number of intervention studies have been carried out with a focus on multimorbidity, and results have not been encouraging,11Smith SM Wallace E O'Dowd T Fortin M Interventions for improving outcomes in patients with multimorbidity in primary care and community settings.Cochrane Database Syst Rev. 2021; 1CD006560 Google Scholar possibly raising an early indication that multimorbidity might not offer a tractable focus for intervention. Even if multimorbidity research can address the weaknesses of definitional imprecision and inadequate accounting for complex disease trajectories, the concept itself might impede the development of appropriate ways to represent the population burden of ill health in ways that generate relevant public health interventions. The estimates and trends presented by Head and colleagues1Lynch R Hanckel B Green J The (failed) promise of multimorbidity: chronicity, biomedical categories, and public health.Crit Public Health. 2021; 32: 450-461Crossref Scopus (2) Google Scholar are important and concerning, and their call for upstream measures—such as clean air policies and taxes on unhealthy food—to reduce risks for long-term illness is welcome. Healthy ageing, addressing inequalities in healthy life expectancy, and intervening on the smaller number of causes of early-onset morbidity might offer a more fruitful approach than focusing on an overly wide-ranging multiplicity of disease diagnoses. We declare no competing interests. Socioeconomic inequalities in accumulation of multimorbidity in England from 2019 to 2049: a microsimulation projection studyThe number of people living with multimorbidity will probably increase substantially in the next 30 years, a continuation of past observed increases partly driven by changing population size and age structure. Inequalities in the multimorbidity burden increase at each stage of disease accumulation, and are projected to widen, particularly among the working-age population. Substantial action is needed now to address population health and to prepare health-care and social-care systems for coming decades. Full-Text PDF Open Access