What leads to depression?

Introduction: Researchers studied twins to estimate how much genes contribute to major depressive disorder.

Participants: 3,460 adult twin pairs (1,420 identical pairs and 2,040 fraternal pairs) aged 25 to 60, drawn from a national twin registry in Denmark (54% women). Race/ethnicity was not reported.

Method: Identical twins share all of their genes, while fraternal twins share about half. Trained interviewers used a structured diagnostic interview to determine whether each twin had ever met the criteria for major depressive disorder. The researchers then calculated how often, when one twin had the disorder, the other twin had it too.

Results and Discussion: When one identical twin had major depressive disorder, the other twin also had it 39% of the time. For fraternal twins, the figure was 18%. Among all participants, 15% had met the criteria at some point in their lives.

Introduction: Researchers followed young adults for eight years to see how stressful life events and family history combine to predict depression.

Participants: 1,040 adults in New Zealand followed from age 18 to age 26 (50% women). Race/ethnicity was not reported.

Method: At age 18, participants reported whether a parent had ever been treated for major depressive disorder. Each year from 21 to 25, they reported serious stressful events, such as losing a job, a breakup, the death of a loved one or being assaulted. At age 26, a clinician who did not know their earlier answers used a structured interview to determine whether they had experienced a major depressive episode in the past year.

Results and Discussion: Among participants with three or more serious stressful events, 33% of those with a parent who had been treated for depression had a major depressive episode at 26, compared with 14% of those without such a parent. Among participants with zero or one stressful event, the figures were 8% and 6%.

Introduction: Researchers tested whether the way students explain their failures predicts depression after a setback.

Participants: 312 first-year students (58% women) aged 18 to 20 at a university in Ireland. Race/ethnicity was not reported.

Method: At the start of the year, students completed a questionnaire about how they explain bad events, for example whether they see a failure as their own fault, as lasting forever and as affecting every part of their life ("I'm stupid, and I'll never be good at anything"), or as caused by temporary, specific circumstances ("I didn't study enough for that test"). Researchers then identified the 120 students who failed at least one major exam in their first term. Two months later, a clinician screened these students for symptoms of major depressive disorder.

Results and Discussion: Among students who failed an exam, 27% of those who tended to see failures as their own lasting, all-encompassing fault had significant depressive symptoms, compared with 9% of those who tended to explain failures by temporary, specific causes. Among students who did not fail an exam, the two groups did not differ significantly.