Ethnic specific associations between body composition and metabolic risk and the role of sex hormones and aromatase among black and white South African women

• Main Author: Tootla, Mehreen
• Other Authors: Goedecke, Julia
• Format: Dissertation
• Language: English
• Published: University of Cape Town 2016
• Subjects: Physiology
• Online Access: http://hdl.handle.net/11427/16775

Includes bibliographical references === Background: Previous evidence has demonstrated ethnic differences in the relationship between body fat distribution and metabolic risk between black and white women. However, the reasons for these differences are not known and may be explained in part by differences in sex hormones. The overall aim of this thesis was therefore to i) examine ethnic-specific associations between body fat and its distribution and cardio-metabolic outcomes (study 1) and ii) examine the associations between sex hormones and subcutaneous adipose tissue (SAT) expression of oestrogen receptors (ERα and ERβ) and aromatase (CYP19A), and body fat distribution and insulin resistance (IR) among black and white women (study 2).Methods: Study 1: In 288 black and 197 white premenopausal women, dual-energy X-ray absorptiometry (DXA) and computed tomography (CT) derived measures of body fat distribution and cardio-metabolic factors including IR (HOMAIR) and lipid levels were measured. Study 2: In a subsample consisting of 13 normal-weight and 15 obese black and 15normal-weight and 12 obese white women, HOMAIR and SI (frequently sampled intravenous glucose tolerance test) and ERα, ERβ and CYP19A gene expression were measured in abdominal and gluteal SAT. Results: Study 1: Compared to white women, black women had less central and greater lower body fat, but had similar IR and lower serum lipid concentrations. Despite these differences, the associations between body fat distribution and measures of IR, as well as TG and HDL-Concentrations were similar in black and white women. Notably, central and peripheral fat deposition was independently associated with IR in both the black and white women, and with TG in the black women. In contrast, the associations between body composition and fasting plasma glucose, TC and LDL-C concentrations differed between black and white women. Fasting glucose concentrations were associated with centralisation of body fat in black but not white women, whereas TC and LDL-C concentrations were associated with centralisation of body fat in white but not black women. In addition to body fat distribution, MVPA was associated with IR in the white women, and contraception use was associated with lipid levels in the black and white women. Study 2: CYP19A expression was positively associated with increased adiposity in black and white women in all three depots. Gluteal ERα was significantly higher and ERβ was significantly lower in the black compared to the white women, irrespective of BMI. Gluteal ERα was negatively associated with trunk fat mass (FM) and HOMAIR in the black women only. Gluteal ERα was significantly lower in obese white compared to normal weight white women. Additionally oestradiol (E2) levels were lower in obese compared to normal-weight white women, but did not differ by ethnicity. Conclusion: Our results indicate that it is important in both black and white populations, to decrease centralisation of body fat. Modifiable risk factors such as MVPA and contraception use should be used as therapeutic targets to prevent and manage CVD. Additionally, oestrogen receptors may be an important determinant of body fat distribution and risk in the black women.