Alterations of Cortisol Homeostasis May Link Changes of the Sociocultural Environment to an Increased Diabetes and Metabolic Risk in Developing Countries: A Prospective Diagnostic Study Performed in Cooperation With the Ovahimba People of the Kunene Region/Northwestern Namibia

Abstract

CONTEXT: Diabetes mellitus is increasingly affecting Africa. OBJECTIVE: Urbanization of the Ovahimba people in Namibia is associated with an increased prevalence of disorders of glucose metabolism, and may thus be attributed to changes of cortisol homeostasis. DESIGN: A prospective, cross-sectional, diagnostic study was applied. SETTING: The study was conducted in the field. Location of the Diabetes Epidemic: Africa and Namibia. PARTICIPANTS: Ovahimba people: group 1 "urban" n = 60, 42 females, 46.3 ± 11.3 years (town); group 2 "rural" n = 63, 44 females, 51.1 ± 12.0 years (seminomadic). INTERVENTIONS: oGTT, sunrise and sunset saliva cortisol, metabolic parameters, questionnaire. MAIN OUTCOME MEASURE: The prevalence of disorders of glucose metabolism (DM, IGT, IFT). RESULTS: The prevalence of disorders of glucose metabolism differed significantly: urban group n = 17(28.3%) vs rural group n = 8(12.7%) (P = 0.04). The saliva cortisol concentrations also differed significantly: sunrise 0.34 ± 0.18 vs 0.12 ± 0.15 μg/dL, sunset 0.18 ± 0.20 vs 0.07 ± 0.09 μg/dL, area under the curve 6.16 ± 3.48 vs 2.28 ± 2.56 μg/dL * 24 h (all P < 0.001). Further metabolic parameters were unfavorably changed in the urban group: hip circumference (P < 0.001), waist circumference (P < 0.001), body mass index (P = 0.014), systolic BP at rest (P < 0.001), diastolic BP at rest (P = 0.002), systolic BP after exercise (P < 0.001), heart rate after exercise (P = 0.007), fasting glucose (P < 0.001), 2-h-glucose by OGTT (P = 0.002), triglycerides (P = 0.04), HDL-cholesterol (P = 0.014), prevalence of the metabolic syndrome (P < 0.001). Physical activity was higher in the rural group, and intake of fast food and sweets were higher in the urban group. CONCLUSIONS: Urbanization of the Ovahimba people is associated with an increasing prevalence of disorders of glucose metabolism and other unfavorable metabolic parameters. Besides changes of lifestyle, this may be attributed to an increased cortisol exposure of the Ovahimba people living in an urban environment.