Depression is also common, with UK prevalence estimated at 4.5 per cent. While incidence varies with age and sex and peaks in older adults (7.5 per cent of females and 5.5 per cent of males aged 55-74 years are estimated to have the condition), the impact can be substantial at any age, with depression the leading cause of disability and premature death in people aged 18-44 years.  

The cause of depression is unknown but it seems likely that biological, psychological and social factors interact. There are certain things that appear to increase the risk of the condition developing, including chronic illnesses such as diabetes, COPD, cardiovascular disease and anything causing long-term pain; medicines such as corticosteroids; life events such as divorce, bereavement, unemployment, poverty and homelessness; genetics; and adverse childhood experiences. Women – particularly those who have recently given birth – are also at higher risk. 

Depression is more than simply a manifestation of low mood. The pain and disability of physical diseases can be exacerbated and lead to increased morbidity and mortality (e.g. there is a higher rate of amputation in people with diabetes who also have depression), an increased risk of substance abuse, an impaired ability to function normally, which can impact on work and relationships, and an increased risk of suicide. The quality of life experienced by someone with depression – and that of their family – can be considerably lower than would otherwise be the case.