INTRODUCTION — Depression is a major public health problem associated with increased functional disability and mortality. In the United States in 2010, the estimated annual economic consequences of unipolar major depression, including direct medical costs and workplace costs, exceeded 200 billion dollars [1].
This topic reviews the epidemiology of unipolar depression in adults. The clinical features, course of illness, assessment, diagnosis, and treatment of depression are discussed separately.
●(See "Unipolar depression in adults: Clinical features".)
●(See "Unipolar depression in adults: Course of illness".)
●(See "Unipolar depression in adults: Assessment and diagnosis".)
●(See "Unipolar major depression in adults: Choosing initial treatment".)
●(See "Unipolar depression in adults: Choosing treatment for resistant depression".)
DEFINITIONS OF DEPRESSION — The term “depression” can be used in multiple ways, which can be confusing; depression may refer to a [2,3]:
●Mood state, as indicated by feelings of sadness, despair, anxiety, emptiness, discouragement, or hopelessness; having no feelings; or appearing tearful. Depressed (dysphoric) mood may be normal or a symptom of a psychopathological syndrome or a general medical disorder.
●Syndrome, which is a constellation of symptoms and signs that may include depressed mood. Depressive syndromes that are typically encountered include major depression, minor depression, or dysthymia (persistent depressive disorder).
●Mental disorder that identifies a distinct clinical condition. As an example, the syndrome of major depression can occur in several disorders, such as unipolar major depression (also called “major depressive disorder”), bipolar disorder, schizophrenia, substance/medication-induced depressive disorder, and depressive disorder due to another (general) medical condition.
PREVALENCE — Unipolar depression is highly prevalent in adults throughout the world.
Prevalence in general medical disorders — Depressive syndromes are highly prevalent across the world in outpatients with general medical disorders and appear to be more common in these outpatients than the general population (see 'Prevalence in general population' below). A meta-analysis identified 83 cross-sectional studies from five continents that included outpatients with general medical disorders (total n >41,000); studies of patients whose depression predated their general medical disorders were excluded [4]. The pooled point prevalence of depression was 27 percent. However, heterogeneity across studies was very large, and the prevalence in different specialties varied from approximately 15 to 50 percent. A subgroup of eight studies compared outpatients (n >3000) with controls who did not have general medical disorders (n >3000), and found that the pooled point prevalence was three times greater in outpatients (18 versus 6 percent).
Prevalence in general population
Worldwide — Depression is highly prevalent in the general population of adults throughout the world. Nationally or regionally representative surveys in 21 countries estimate that the 12-month prevalence of unipolar major depression across all countries is 5 percent [5]. In addition, the lifetime prevalence of unipolar major depression plus persistent depressive disorder (dysthymia), according to surveys in 14 countries, is approximately 12 percent [6]. Among the 14 countries [6]:
●The prevalence of unipolar major depression plus persistent depressive disorder in developed countries (United States and Europe) is approximately 18 percent.
●In resource-limited countries (eg, People’s Republic of China, Mexico, and Brazil), the estimated lifetime prevalence is 9 percent.
This twofold difference between developed and resource-limited countries may reflect true variation in the determinants of depression due to cultural or genetic factors, sample selection biases, and problems with the cross-cultural portability of diagnostic criteria [7,8].
United States — Depression is highly prevalent in the general population of the United States. A nationally representative survey of adults in the United States found that the 12-month prevalence of unipolar major depression was 10 percent, and the lifetime prevalence was 21 percent [9].
The prevalence of persistent depressive disorder (dysthymia) appears to be less than that of unipolar major depression. As an example, a nationally representative survey found that the lifetime prevalence of persistent depressive disorder was 3 percent [10].
Other countries — Depressive syndromes are highly prevalent in the general population of many countries beyond the United States. Nationally or regionally representative community surveys in different countries found that the 12-month prevalence of unipolar major depression was as follows [5]:
●Argentina – 4 percent
●Belgium – 5 percent
●Brazil – 10 percent
●Bulgaria – 3 percent
●China (People’s Republic) – 2 percent
●Colombia – 5 percent
●France – 6 percent
●Germany – 3 percent
●Iraq – 4 percent
●Israel – 6 percent
●Italy – 3 percent
●Japan – 2 percent
●Lebanon – 5 percent
●Mexico – 4 percent
●Netherlands – 5 percent
●Nigeria – 1 percent
●Peru – 3 percent
●Portugal – 7 percent
●Romania – 2 percent
●Spain – 4 percent
AGE OF ONSET — Multiple studies consistently indicate that in the general population of the United States, the average age of onset for unipolar major depression and for persistent depressive disorder (dysthymia) is approximately 30 years [10,11]. As an example, a nationally representative survey of adults found that onset of the first lifetime episode of major depression occurs at age 29 years [9].
DEMOGRAPHIC RISK FACTORS — Several sociodemographic factors are associated with an increased risk for unipolar depression.
Age — Within the general population of the United States, major depression is more common in younger adults than older adults. A nationally representative survey found that the 12-month prevalence of unipolar major depression was greater in younger age groups than adults aged 65 years or more (11 to 13 versus 5 percent) [9]. In addition, the lifetime prevalence was greater in younger age groups (20 to 23 versus 14 percent).
In addition, the prevalence of depression in older adults declines as they age. A community survey of adults aged 55 years and older in the United States found that the 12-month prevalence of major depression decreased significantly with increasing age [12].
However, certain groups of older adults have higher rates of depression compared with older adults in general. The prevalence in older primary care patients is comparable to that of younger patients [13,14]. Depression is even more common in older adults with a greater burden of medical illness, including residents of assisted living or skilled nursing facilities, recipients of home health care, and patients suffering from a wide range of acute and chronic medical conditions [15-18].
Income — In the general population of the United States, the prevalence of major depression is greater among individuals with less income. A 2013 nationally representative survey in the United States found that the 12-month prevalence of unipolar major depression in lower household income categories is greater compared with the highest family income category ($70,000 or more; 10 to 14 versus 8 percent) [9]. However, the differences in the lifetime prevalence of major depression between lower categories and the highest category are less pronounced (20 to 23 and 20 percent).
Marital status — A nationally representative survey in the United States found that the prevalence of unipolar major depression is highest in adults who are divorced, separated, or widowed [9]:
●Twelve-month prevalence
•Married/cohabitating – 8 percent
•Never married – 13 percent
•Divorced, separated, or widowed – 14 percent
●Lifetime prevalence
•Married/cohabitating – 19 percent
•Never married – 21 percent
•Divorced, separated, or widowed – 26 percent
Race/ethnicity — A nationally representative survey in the United States found that the prevalence of unipolar major depression among different racial groups is highest in Native Americans and lowest in Asians/Pacific Islanders [9]:
●Twelve-month prevalence
•Asian/Pacific Islander – 7 percent
•Black – 9 percent
•Hispanic – 10 percent
•Native American – 16 percent
•White – 11 percent
●Lifetime prevalence
•Asian/Pacific Islander – 12 percent
•Black – 15 percent
•Hispanic – 16 percent
•Native American – 28 percent
•White – 23 percent
Sex — Within the general population of the United States, as well as other countries, the prevalence of depressive syndromes is approximately two times greater in females than males [19,20]:
●A nationally representative survey in the United States found that the 12-month prevalence of unipolar major depression in females and males is 13 and 7 percent [9]. In addition, the lifetime prevalence in females and males is 26 and 15 percent.
●Surveys of community-dwelling adults in 15 countries (including the United States) found that the lifetime prevalence of major depression and persistent depressive disorder (dysthymia) were each 1.9 times higher in females compared with men [21].
The prevalence rates for females and males may differ because the etiology of depression in each sex is different [22].
SUMMARY
●Across the world, the point prevalence of depression in outpatients with general medical disorders is roughly 25 percent and depressive syndromes appear to be more common in outpatient clinical settings than the community (general population). (See 'Prevalence in general medical disorders' above.)
●The estimated 12-month prevalence of unipolar major depression in the worldwide general population is 5 percent. In addition, the lifetime prevalence of unipolar major depression plus persistent depressive disorder (dysthymia) is approximately 12 percent. (See 'Worldwide' above.)
●Among the general population of adults in the United States, the estimated 12-month prevalence of unipolar major depression is 10 percent, and the lifetime prevalence is 21 percent. (See 'United States' above.)
●In the general population of countries beyond the United States, the estimated 12-month prevalence of unipolar major depression ranges from 1 to 10 percent. (See 'Other countries' above.)
●The average age of onset for unipolar major depression and for persistent depressive disorder (dysthymia) in the general population of the United States is approximately 30 years. (See 'Age of onset' above.)
●Within the general population of the United States, major depression is more common in younger adults, individuals with less income, and is highest in adults who are divorced, separated, or widowed. (See 'Age' above and 'Income' above and 'Marital status' above.)
●In the United States, the prevalence of unipolar major depression among different racial groups is highest in Native Americans and lowest in Asians/Pacific Islanders. (See 'Race/ethnicity' above.)
●The prevalence of depressive syndromes in the worldwide general population is approximately two times greater in females than males. (See 'Sex' above.)
