According to the World Health Organization, depressive disorder, otherwise known as depression, affects approximately 280 million people globally. Though depression is a mood disorder, it has a strong relationship with physical health. Harmful behaviours that can be attributed to depression, e.g. alcohol dependence, can be risk factors for physical health conditions such as cancer and cardiovascular disease. Additionally, difficulties in managing physical health can result in depression, or worsen existing depressive symptoms. Multiple studies have assessed the relationship between depression and the coexistence of other health conditions; however, these studies have had a short follow-up period. Additionally, many of the studies measured a small number of health conditions (between three and 15 conditions), when it has been recommended that over 50 conditions should be used. In research published in February 2025 in PLOS Medicine, Kelly J Fleetwood and colleagues measured the presence of multiple health conditions using 69 long-term health conditions to assess the relationship between the history of depression and the development of additional health conditions. The study found that individuals with a previous depression diagnosis had developed additional health conditions at a 30% faster rate compared to those not diagnosed, after adjusting for all sociodemographic characteristics.
To observe the effects of the history of depression and rates of health condition development, this study collected baseline data of participants from the UK Biobank with linked primary care data. UK Biobank, a large prospective population-based cohort study, recruited over 500,000 participants aged 40–69 years from 2006–2010 in England, Scotland, and Wales. UK Biobank participant data was then linked to hospitals, cancer registries, and death records from England, Scotland, and Wales. Diagnosis of depression was identified from linked primary care or hospital records, or self-reported diagnosis in the baseline assessment. The 69 long-term health conditions were identified using information from the baseline assessment and the primary care, hospital registry, and death records. In total, 172,556 participants were included in the study, 30,770 of which had a history of depression at baseline. Participants with a history of depression were more vulnerable to the development of additional health conditions, developing an average of 0.2 additional physical health conditions per year compared to 0.16 conditions for those without a history. Additionally, those with a history of depression developed new long-term physical health conditions 30% and 10% faster, respectively, than those without a history, after adjusting for sociodemographic factors and fully adjusting for potential mediators.
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This study by Fleetwood and colleagues provides evidence of depression being a key risk factor in long-term physical health conditions and illustrates the importance of treating physical and mental health conditions in tandem. However, this study only focused on middle-aged and older individuals, meaning the relationship depression has with disease development may be different in younger individuals. GlobalData epidemiologists forecast that in the eight major markets (8MM: US, France, Germany, Italy, Spain, UK, Japan, Canada), diagnosed prevalent cases of major depressive disorder, the severe form of depression, in men and women ages 18 years and older will increase from 18.9 million cases in 2025 to 19.1 million cases in 2029.
