Introduction

COPD is one of the most prevalent chronic diseases worldwide affecting an estimated 12.4% of those aged 40?years and above [1]. Comorbidity is common in patients with COPD and is associated with a poorer overall prognosis [2]. The comorbidities commonly described in association with COPD are multisystem and include coexistent respiratory pathology, cardiovascular disease, endocrinopathies, musculoskeletal pathology, and neuropsychiatric conditions (figure 1). While many of these comorbidities have shared risk factors (e.g. cigarette smoking in cardiovascular disease), it is increasingly recognised that systemic inflammation is present in COPD, and is an independent mechanism via which multimorbidity develops. Abnormally high levels of circulating acute phase inflammatory biomarkers, such as interleukin (IL)-6, C-reactive protein (CRP) and fibrinogen [3], have been detected in patients with COPD, even in those with only moderate disease. Systemic inflammation is associated with an increased risk of cardiovascular disease, infection, diabetes, impaired cognition, anxiety and lung cancer [4]. In addition, low physical activity is associated with higher mortality and hospitalisations in those with COPD and is increasingly recognised as a risk factor for comorbidity [5]. Multimorbidity in COPD leads to reduced quality of life, increased healthcare use and increased mortality. Despite this, many comorbidities remain undiagnosed [2]. Understanding and addressing the presence of comorbidities in COPD is essential to improve the quality of life and survival of individuals. In this review, we outline the comorbidities most commonly associated with COPD, their incidence and prevalence, their impact on clinical course and management, and discuss strategies to effectively prevent and manage them. A summary can be found in table 1.