Associations among education, cortisol rhythm, and BMI

Nutrition Research Newsletter, April, 2006

Stressful events and circumstances may contribute importantly to the social gradient in obesity. Social stressors such as low socioeconomic status (SES) may affect obesity not only through unhealthful diet and activity patterns but also through neuroendocrine reactions to stress. Stress-induced activation of the central nervous system and autonomic-neuroendocrine axes is linked to the development of most risk factors for stroke, cardiovascular disease, type 2 diabetes, and some cancers. Difficult conditions of living related to low SES are associated with a variety of neuroendocrine markers of chronic stress. Chronic stress is a prolonged state of homeostatic imbalance that occurs from exposure to stressors embedded in living or working environments or to repeated acute-incident stressors with effects that persist well beyond the initiating event. Individuals of low SES tend to have chronically elevated cortisol and neuroendocrine hormones responsive to stressful episodic threats. Such responses could partially explain how "upstream" factors underlying file SES-health gradient, including conditions of living and social anxiety, may influence obesity. Stressful conditions of living could impair resilience needed to eat healthfully, and anxiety could inhibit coping ability and invoke biological responses related to obesity and chronic disease. While it is known that appetite for high-energy dense foods may be promoted by cortisol secretions, the relationship between biological responses and stress and obesity has received far less attention.

This study sought to evaluate, in a field setting, whether delta cortisol was related to BMI, education, and positive affect, and whether the relationship between delta cortisol and BMI varied with education or positive affect. Delta cortisol, the difference between awakening and midday cortisol concentrations signifying diurnal decline, was used as a biomarker of chronic stress. Cortisol normally follows a daily diurnal rhythm, with lowest concentrations occurring close to midnight. Concentrations begin to rise during sleep, with a peak occurring on or shortly after awakening, between 5:00 am and 8:00 am, followed by a rapid decline for the next several hours and a gradual decline over the remainder of the day. Low diurnal decline, or cortisol reactivity to acute stress signifying dysregulation of the HPA axis, is related to higher BMI, greater waist girth, and a greater incidence of cardiovascular disease, diabetes, and hypertension. A reduced diurnal variability of cortisol is related to chronic stress, particularly vital exhaustion, chronic fatigue, post-traumatic stress disorder, and poor relationship functioning among women.

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 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. For participants with complete data (n = 129), BMI was greater for women with less than high school education and those who completed high school relative to women with greater than a high school education. Delta cortisol was inversely related to BMI. Education positively modified the inverse relationship between delta cortisol and BMI. Positive affect was negatively associated with BMI and positively modified the inverse association between delta cortisol and BMI.

In this sample of blue-collar women, education and delta cortisol were inversely associated with BMI, and the magnitude of the relationship between delta cortisol and BMI varied according to education. For delta cortisol, positive values indicate a typical circadian rhythm, whereas lower or negative values indicate a less variant or atypical pattern representing biological response to chronic stress. These findings were repeated in a second model that also tested moderation by positive effect of the association between delta cortisol and BMI. For blue-collar female employees in industrial sites in eastern North Carolina, the relation between chronic stress and BMI suggests a need for interventions that target broader social and socioeconomic influences on obesity. Effective responses for obesity prevention or treatment in this population may also require stress management, with attention to particular stressors related to low delta cortisol and positive effect. The strong influence of education in attenuating the link between chronic stress and BMI supports policy interventions to reduce inequity in educational opportunity. For disadvantaged populations characterized by high chronic stress, improved educational attainment may hold promise as a broad approach complementary to specific strategies to offset the high prevalence and increasing incidence of overweight and obesity.

M Daniel, DS Moore, S Decker, et al. Associations among education, cortisol rhythm, and BMI in blue-collar women. Obes Res; 14(2):327-335 (February 2006) [Correspondence: Dr. Mark Daniel, Centre Hospitalier de l'Universite de Montreal, Hotel-Dieu, Centre de Recherche, Axe Sante des Populations, 3875, rue Saint-Urbain, Montreal, Quebec H2W 1V1, Canada. E-mail: mark.daniel@umontreal.ca]