Social isolation, inflammation, and cancer mortality from the National Health and Nutrition Examination Survey - a study of 3,360 women

BACKGROUND: This study evaluates the role of social isolation on inflammation and cancer mortality among women. METHODS: Data were abstracted from the U.S. National Health and Nutrition Examination Survey from 1988 to 1994. The Social Network Index was used to assess participants' degree of social isolation. C-reactive protein and fibrinogen levels were included as markers of inflammation. We used the National Death Index to identify causes and dates of mortality. Chi-square and multivariable Cox regressions were employed for statistical analyses. RESULTS: Of 3360 women (median age: 54 years), the most isolated, very isolated, somewhat isolated, and not isolated comprised 14.5, 30.2, 37.1, and 18.2% of the sample, respectively. The most isolated participants were more likely to have low income (56.8% vs 12.2%, p < 0.001), have fewer years of education (40.8% vs 12.3%; p < 0.001), have low physical activity (27.3% vs 14.7%; p < 0.003), be obese (32.5% vs 24.4%; p = 0.02), and be current smokers (34.2% vs 10.3%; p < 0.001) compared to the not isolated ones. Mean fibrinogen levels increased with degree of social isolation (p = 0.003), but C-reactive protein showed no association (p = 0.52). Kaplan-Meier estimates indicated higher cancer mortality rates among participants with elevated fibrinogen levels, though not with statistical significance (p = 0.08). Furthermore, there was no association between social isolation and cancer mortality (p = 0.54). On multivariate analysis, obesity (HR = 1.56; 95% CI: 1.11-2.18), higher education (HR = 1.36; 95% CI: 1.01-1.83), and smoking (HR = 4.42, 95% CI: 2.84-6.88) were independent predictors for cancer mortality, while high physical activity predicted for lower mortality from cancer (HR = 0.67, 95% CI: 0.51-0.87). However, social isolation was not a predictor. CONCLUSION: Social isolation among women was associated with an increased level of fibrinogen, but not associated with cancer mortality. The relationship between inflammation and cancer mortality warrants further investigation.