Participants were adults ages 25 to 75 at the baseline assessment which occurred from 1995–1996.  Four thousand six hundred and forty-two participants completed both the baseline assessment and the 10-year follow-up assessment between 2004 and 2006 and were included in the analyses.  Researchers used the Composite International Diagnostic Interview Short Form to assess whether participants had experienced a major depressive episode during the 10-year study. The quality of social relationships and social isolation were measured using telephone interviews and written questionnaires. 

Key Findings:

• The overall quality of social relationships was associated with a significantly higher risk of depression. 
• Participants with the lowest quality social relationships had more than double the risk of depression than those with the highest quality relationships.
• Social isolation did not predict future depression or moderate the effect of relationship quality.

Interventions for treating patients with depression should consider the importance that relationships play.  This study demonstrates the significance of spouse/partner relationship quality indicating that couples therapy may be an effective preventive treatment for major depression.