How common is depression and who gets it?

Depression is one of the most frequently occurring mental illnesses or the ‘common cold’ of psychiatry. In 1996, the Director General of the World Health Organization estimated that 340 million people suffer from mood disorders worldwide. Depression is the second most common mental illness after anxiety, but the most common serious mental illness.

Epidemiological studies report a lifetime risk of developing depression of between 8–12 per cent for men and 20–26 per cent for women (Arch Gen Psychiatry 1981 38:10391046).

In many studies, a further 8 to 20 per cent of community samples report depressive symptoms that do not meet the threshold for major depression but nevertheless cause increased mortality, disability and poor social functioning.

Who is at high risk?

No one is immune from depression: it occurs in people of all ages, all social classes, all countries and all cultural settings.
Gender
Women are twice as likely to develop depression as men. Many explanations have been suggested, but psychosocial factors would appear the most likely, e.g. the greater stress on women of maintaining multiple roles such as homemaker, professional wife and mother.
Age
The risk of depression was thought to increase with age, but recent studies now show the average age onset has dropped from the late 40s to the late 20s since World War II (JAMA 1996 276:293299).
Socioeconomic status
Rates of depression decline with increased income and education. More severe forms are also associated with lower socioeconomic status (Arch Gen Psychiatry 1994 51:919).
Family history
Depression is two to three times more common among the family of depressed patients. About 20 per cent of relatives of depressed individuals are affected compared to 7 per cent of relatives of controls (Arch Gen Psychiatry 1982; 39:13971403).
Marital status
Separated or divorced people have a two to four times greater risk of depression than married. Divorced or separated men seem to be at higher risk than women.
Depression in the elderly
Depression is common among the elderly, although it often goes undetected and untreated in this patient group. Estimates of prevalence are about 15 per cent and depression is twice as common in those suffering from physical illness. Depression is also associated with high chronicity and a considerable risk of relapse and suicide in the elderly. Elderly sufferers display more vegetative signs such as insomnia, fatigue, constipation and weight loss, rather than sadness or dysphoria. Cognitive disturbances are also often misattributed to physical illness, dementia or the ageing process itself.

What about children?

In the last 20 years depression is increasingly being recognized to affect children and adolescents. Children from a broken home, who have lost a parent early in life, suffer from neglect or live in inner–city areas with high rates of poverty, unemployment and crime are more vulnerable to depression.

Depression in childhood can lead to impaired school performance, poor relationships, and increased tobacco and substance usage.