Characteristic of Participants
provides baseline characteristics of the 4,642 study participants. Women comprised just slightly more than half of the sample and 92% were white. Five hundred fifty-nine participants (12.3%) had a major depressive episode at baseline. The mean score on the overall quality of social relationships was 1.82. Participants more commonly reported strain rather than lack of support in their social relationships. The majority did not have markers of social isolation.
Relationship between Quality of Social Relationships and Depression
We first examined whether the overall of quality of social relationships at baseline predicted occurrence of major depressive episodes at follow-up. Across all types of social relationships, poor quality in core relationships was associated with a significantly higher risk of depression (adjusted odds ratio [AOR], 2.65; 95% CI, 1.86–3.76), even after accounting for the predictive power of baseline major depression and other covariates. In secondary analyses including all types of social relationships, both strain (AOR, 2.03; 95% CI, 1.49–2.76) and lack of support (AOR, 1.79; 95% CI, 1.36–2.36) were also associated with increased risk of depression (). In sensitivity analysis among partnered participants who did not have a major depressive episode at baseline (n
3,154), results were still highly significant (for overall poor quality: AOR, 2.54; 95% CI, 1.71–3.76; for social strain: AOR, 2.33; 95% CI, 1.64–3.29; for lack of social support: AOR, 1.57; 95% CI, 1.14–2.16).
Risk of major depressive episode at ten-year follow-up as a function of overall quality of social relationships, social support, and social strain.
In secondary analyses, we assessed relationships only with family and friends, including all participants, even those without a partner. Again we found that overall poor quality in relationships was a significant predictor of depression. Additionally, sensitivity analysis among participants who did not have a major depressive episode at baseline (n
4,083) also showed significant results.
Relationship between Quality of Different Types of Social Relationships and Depression
The type of social relationship also affected depression risk (). In this secondary analysis, poor overall quality of relationship with one’s spouse/partner (AOR, 1.47; 95% CI, 1.16–1.87) and family members (AOR, 1.45; 95% CI, 1.10–1.90) significantly and independently increased risk of depression. In contrast, the overall quality of relationships with friends did not independently predict subsequent depression (AOR, 1.21; 95% CI,.84–1.72).
Risk of major depressive episode at ten-year follow-up as a function of type of social relationship with overall poor quality at baseline.
Similarly, in sensitivity analysis where participants without a spouse or partner were included, poor quality of relationships with family members but not friends significantly increased risk of depression. In the subset of participants without major depression at baseline (n
3,133), poor quality of relationship with one’s spouse/partner (AOR, 1.46; 95% CI, 1.10–1.93) significantly and independently increased risk of depression, but results were not significant for family members (AOR, 1.27; 95% CI,.90–1.79) or friends (AOR, 1.43; 95% CI,.95–2.16).
Predicted Probability of Depression Depending on Quality of Social Relationships
Using our multivariable logistic regression model from our primary analyses, we estimated the composite effect of the overall quality of participants’ social relationships with family, friends, and spouse/partner at baseline on likelihood of developing depression ten years later. Those with the highest quality social relationships (top decile) had just a 6.7% chance of major depression (95% CI, 5.3–8.1; p<.001), whereas those with the lowest quality (bottom decile) had a 14.0% chance (95% CI, 12.0–16.0; p<.001). presents the estimated risk of depression, illustrating a “dose-dependent” effect of impairment in quality of social relationship on risk for major depression.
Predicted probability of depression.
Relationship between Social Isolation and Depression
Data on frequency of social contact were available for relationships with family, friends, and neighbors. In the model, lack of contact with each type of social relationship at baseline was included as a separate predictor variable. Results indicated that lack of social contact, whether with family (AOR, 1.02; 95% CI,.95–1.09), friends (AOR, 1.00; 95% CI,.94–1.06), or neighbors (AOR, 1.03; 95% CI,.96–1.11), did not predict risk of depression. Furthermore, being married (AOR, 1.12; 95% CI,.88–1.44) or having a romantic partner (AOR, 1.10; 95% CI,.85–1.42) at baseline was not associated with future depression.
Interactive Effects of Social Isolation and Quality of Social Relationships
We were interested in whether frequency of social contact acted as a moderator on the impact of overall quality of social relationships on depression. In the case of both family (AOR, 2.72; 95% CI,.67–11.1) and friends (AOR,.89; 95% CI,.42–1.90), lack of contact did not significantly interact with quality of relationship. We also examined whether there was an interaction between quality of social relationships variables and depression at baseline. In models for overall quality of relationships with family, friends, and spouse/partner, there were no interactions found.