suggesting that it may be precipitated by inhaled corticosteroid therapy. COPD patients are current or previous smokers and are at increased risk of lung cancer. Metabolic conditions are also important comorbidities, and this issue of the ERM includes chapters that address obesity in malnutrition in COPD, obstructive sleep apnoea, and osteoporosis, which is one of the most common comorbidities in COPD and is potentiated by the effect of inactivity and corticosteroids. Diabetes affects both stable and exacerbated COPD, and improved diabetic control may benefit exacerbation outcome. Associations have been shown between exacerbation frequency and gastro-oesophageal reflux that will be discussed in this issue of the ERM, though the actual mechanisms of reflux in COPD are not clear and may relate to the mechanical effects of hyperinflation. Inactivity is related to prognosis in COPD and skeletal muscle dysfunction needs to be assessed and targeted. Psychological disease (anxiety and depression in particular) is often present in COPD and must be targeted it is particularly common in patients who have a higher exacerbation risk. Thus, clinical programmes for the management of COPD patients must not only treat airways disease but should also assess and manage the associated comorbidities. This will make COPD management a much more complex, long-term process in the future, requiring multi-disciplinary teams with relevant specialist interests. It is essential that clinical trials include and, wherever possible, specifically target patients with comorbidities, as respiratory therapies may improve comorbidities. At the same time, any adverse effect of therapies on comorbidities in an increasingly ageing population must be recognised early and where patients require multiple pharmacological approaches, optimal adherence to therapy must be ensured. Current therapies for COPD are actually relatively limited and thus it is possible that therapies targeting comorbidities may have a significant impact on health status and mortality in COPD. Further research and evidence is required to inform future guidelines on the relationship of complex comorbidity in COPD. We hope that you will find this issue of the ERM a useful resource that aids understanding of the role of comorbidity in COPD and the way in which comorbidity potentially influences disease management. This book will be of benefit to a wide number of healthcare professionals, including clinicians, nurses and allied healthcare professionals, but it will also be of interest to those specialising in the management of comorbidities, such as cardiologists and gastroenterologists. The chapters are up to date and well referenced, and will stimulate novel ideas for research and inspire healthcare professionals in training. We are very grateful to all the authors who have contributed excellent chapters on such an important and yet relatively poorly understood and researched topic. x