In a recent meta-analysis, which included 90 studies from 30 countries (from 1994-2014) following findings were observed:
- Point Prevalence for Depression = 12%
- 1 year Prevalence for Depression = 7.2%
- Lifetime Prevalence for Depression = 10.8%
Aetiology & Risk Facors:
Depression has heritability of about 40% (women>men) . Genes for depression overlap with genes for anxiety and neuroticism. Genes that might have a role in depression are those that are involved in:
- encoding of serotonin (HTR1A)
- serotonin transporter (5HTTP/ SLC6A4)
- Dopamine receptor (DRD4)
- Dopamine Transporter (SLC6A3)
2. Stressful Life Events & Childhood Adversities:
Life event most often associated with the development of depression is losing a parent before the age of 11 yrs.
Environmental stressor most often associated with the onset of depression is the loss of spouse. Another risk factor is unemployment.
Approximately 60-80% of patients with 1st depressive episode have experienced stressful life events in a 6 month period prior to the onset of depression; whereas prevalence of stressful life events is decreased to 20-40% or less in relation to subsequent depressive episodes.
Before Puberty : Prevalence of depression is higher in boys compared to girls.
After Puberty : Prevalence of depression starts increasing in females after puberty. Women to men ratio after puberty = 2:1
A women’s unequal status may make women more vulnerable to depression. But, it is notable that in societies where women have gained a better level of status, the ratio has not significantly changed. Evidence suggests that biological differences such as variations in Hormonal levels do account for at least part of this difference.
Mean age for onset of depressionis is 40yr. Some studies suggest that the incidence of depressive disorder is increasing among younger persons.
5. Marital Status:
Depression is more common in divorced/separated than married persons.
7. Physical Illness:
Chronic & severe physical illness is associated with an increased risk for depression.
In case of depression in Parkinson’s Disease, there is possibility of shared neurotransmitter abnormalities.
In Post-stroke depression, location of the lesion can contribute to the rate of depression which suggests a neuroanatomical/ neurotransmitter connection between the two.
For Non-CNS disorders, such as Acute Myocardial Infarction, Diabetes and Cancer the mechanism for this association is less clear.