Associations among education, cortisol rhythm, and BMI in blue-collar women

Objective: This study sought to test whether a biological measure of chronic stress, Delta cortisol, was related to BMI and whether the relationship between Delta cortisol and BMI varied according to education and positive affect, Research Methods and Procedures: One hundred fifty-four women from a blue-collar women's health project in 11 industrial sites in rural North Carolina provided saliva for cortisol assays for a substudy on "stress." Delta Cortisol, the difference between awakening and midday cortisol measures representing diurnal decline, was calculated (lower values = greater stress). BMI was regressed on Delta cortisol, education, and positive affect. Analyses were controlled for age, race, and worksite. Standardized beta-coefficients were calculated. Results: For participants with complete data (n = 129), BMI was greater (beta; 95% confidence interval) for women with less than high school education (0.56; 0.18, 0.94) and those who completed high school (0.26; -0.05, 0.57) relative to women with greater than a high school education (p = 0.009). Delta Cortisol was inversely related to BMI (-0.32; -0.59, -0.05; p = 0.022). Education positively modified the inverse relationship between Delta cortisol and BMI (p = 0.047). Positive affect was negatively associated with BMI (-0.44; -0.82, -0.06; p = 0.026) and positively modified the inverse association between Delta cortisol and BMI (0.33; -0.03, 0.69; p = 0.074). Discussion: Education and Delta cortisol were inversely related to BMI, and the magnitude of the association between Delta cortisol and BMI was buffered by higher education. Positive affect was inversely related to BMI. Chronic stress is associated with higher BMI, with this relation attenuated by higher education and, possibly, a positive affect.