New research reveals how chronic illnesses tend to cluster together – and why it matters
A new systematic review led by the School of Medicine has shed light on how chronic diseases tend to cluster together in adults, revealing important differences based on age and sex. The findings offer vital insights for healthcare systems seeking to improve care for patients with multiple long-term conditions (MLTCs), also known as ‘multimorbidity.’
Today, one in every three adults globally lives with MLTCs, with this prevalence expected to double in the next two decades. People with MLTCs often require complex care and multiple medications, leading to frequent hospital visits and increased use of healthcare services, all of which has a significant economic impact.
This new article, published in PLOS One, is the only systematic review to examine multimorbidity by age, sex and socioeconomic strata and the largest investigating multimorbid clusters to date. It developed from dissertation research conducted by 2022 BSc (Hons) Medicine graduate Dr Nataysia Mikula-Noble, who co-authored the article with Population and Behavioural Science Research Division Head Prof. Colin McCowan, St Andrews medical librarian Vicki Cormie, and Dr Rebecca Eilidh McCowan (University of Glasgow School of Medicine). The team analysed data from 125 international studies, identifying nearly 950 disease clusters and categorising them into 59 broad groups.
These results revealed that certain disease clusters are particularly common, with the most frequently observed combination including heart disease, high blood pressure, diabetes, and related conditions. This group of illnesses, known as the cardiometabolic cluster, was identified in people of all ages. Other common clusters included diabetes and high blood pressure and a mix of muscle, nerve, and mental health conditions.
The researchers also discovered that different age groups tend to experience different clusters. They found that while young adults (18-44 years) often exhibit clusters involving mental health and musculoskeletal issues, middle-aged adults (45-64 years) most commonly experience diabetes and high blood pressure together. Meanwhile, older adults (65 years or above) tend to exhibit clusters involving frailty, mental decline, and respiratory or heart problems.
While the review revealed that most clusters appear in both men and women, mental health-related clusters were slightly more common in younger women.
Unlike for age and sex, clustering patterns based on socioeconomic status were difficult to identify due to a lack of data. Only four of the 125 studies examined how this factor affects disease clustering – highlighting a significant gap in current research.
“This review highlights the importance of understanding how diseases co-occur in different population groups,” said Prof. McCowan, noting that St Andrews School of Medicine plans to embed multimorbidity concepts into its curriculum. “With multimorbidity on the rise across all age groups, healthcare systems must adapt to treat not just individual conditions but the combinations that commonly arise together.”
Dr Mikula-Noble agreed, highlighting the potential benefits of a multimorbidity-informed approach to care: “Our findings suggest that tailoring healthcare services to the most prevalent disease clusters in specific age and sex groups could lead to more efficient, holistic care and better outcomes for patients.”
Although further research is needed to better identify disease clusters and the factors that influence them, this study marks a crucial step forward in recognising the complexity of multimorbidity and its implications for medical education, public health policy, and clinical care.