Stress-induced inflammatory responses in women: effects of race and pregnancy

Abstract

Objective: African Americans experience preterm birth at nearly twice the rate of whites. Chronic stress associated with minority status is implicated in this disparity. Inflammation is a key biological pathway by which stress may affect birth outcomes. This study examined the effects of race and pregnancy on stress-induced inflammatory responses.

Methods: Thirty-nine women in the second trimester of pregnancy (19 African American, 20 white) and 39 demographically similar nonpregnant women completed an acute stressor (Trier Social Stress Test). Psychosocial characteristics, health behaviors, and affective responses were assessed. Serum interleukin (IL)-6 was measured at baseline, 45 minutes, and 120 minutes poststressor.

Results: IL-6 responses at 120 minutes poststressor were 46% higher in African Americans versus whites (95% confidence interval = 8%-81%, t(72) = 3.51, p = .001). This effect was present in pregnancy and nonpregnancy. IL-6 responses at 120 minutes poststressor tended to be lower (15%) in pregnant versus nonpregnant women (95% confidence interval = -5%-32%, p = .14). Racial differences in inflammatory responses were not accounted for by demographics, psychological characteristics, health behaviors, or differences in salivary cortisol. Pregnant whites showed lower negative affective responses than did nonpregnant women of either race (p values ≤ .007).

Conclusions: This study provides novel evidence that stress-induced inflammatory responses are more robust among African American women versus whites during pregnancy and nonpregnancy. The ultimate impact of stress on health is a function of stressor exposure and physiological responses. Individual differences in stress-induced inflammatory responses represent a clear target for continued research efforts in racial disparities in health during pregnancy and nonpregnancy.

Keywords: acute stress; affective response; inflammatory response; interleukin-6; pregnancy; racial disparities.

Fig 1. Inflammatory Responses to the Trier Social Stress Test in Pregnant and Nonpregnant Women

Controlling for baseline, IL-6 levels at 120 minutes post-stressor were 46% higher in African Americans versus Whites (95% CI: 18% to 81%; t(72) = 3.51, p = .001). This effect of race was significant during pregnancy and nonpregnancy. Note: Data are pictured in raw values. Analyses were conducted using log-transformed values.

Fig 2. Cortisol Responses to the Trier Social Stress Test in Pregnant and Nonpregnant Women

At baseline, cortisol was significantly higher in pregnant women than in non-pregnant women (t(72) = 15.30, p < .001). A non-significant trend was seen for lower baseline cortisol among African Americans versus Whites (t(72) = 2.65, p = .11). The AUC of cortisol across the study session was significantly higher among pregnant versus non-pregnant women (t(75) = 4.45, p <.001) and marginally lower among African Americans versus Whites (t(75) = 1.77, p = .08). Note: Data are pictured in raw values. Analyses were conducted using log-transformed values.

Fig 3. Changes in Positive Affect in Response to the Trier Social Stress Test

Pregnant women reported significantly less positive affect at baseline as compared to non-pregnant women (F(1,74) = 12.6, p < .001). Controlling for baseline positive affect, positive affect immediately post-stressor or 120 minutes post-stressor did not differ based on race or pregnancy status (ps ≥ .06).

Fig 4. Changes in Negative Affect in Response to the Trier Social Stress Test

Women did not differ in negative affect at baseline based on either race or pregnancy status. Immediately post-stressor, pregnant women had a significantly lower increase in negative affect than nonpregnant women (t(74) = 7.65, p = .007). This effect was driven by pregnant Whites who had lower increases in negative affect than either nonpregnant African Americans or nonpregnant Whites (ps ≤ .01).