Metabolic and hormonal studies in South African women of Indian and African origin
Date
2010-04-13T08:22:02Z
Authors
Waisberg, Rita
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Abstract
Introduction: The data published by the Medical Research Council of South Africa
demonstrated that cardiovascular disease and diabetes mellitus are the second and tenth
leading causes of death in South Africa, respectively (Bradshaw et al.,2003). The prevalence
of obesity is higher in the African than Indian population (Puoane et al., 2002), whereas
cardiovascular diseases (CVD) and diabetes are more common in the latter population (Omar
et al., 1994, Joffe et al., 1994). Diabetes and hypertension has been related with abdominal
obesity in a number of studies conducted in the African and mixed-ancestry communities of
the Western Cape (Steyn et al., 1996, Levitt et al., 1993). The reason for the high prevalence
of obesity in the African population is not known however it is known that the aetiology of
obesity involves both environmental and genetic factors (Grundy, 2004).
Objective: The main aim of this project was to ascertain the role of metabolic, hormonal,
anthropometric and environmental factors in the pathogenesis of obesity-related disorders in
two South African ethnic groups namely Indian and African women. These populations were
chosen because of the wide differences in risk factors for the development of CVD and
diabetes reported in these groups.
Subjects and methods: Plasma and serum samples were taken during a 5-hour OGTT from
20 lean, 20 obese, 20 obese type 2 diabetic patients, and 10 overweight women of African and
Indian origin, i.e. 140 subjects in total. All participants were recruited from an urban
population of women residing in the Greater Johannesburg area. Serum insulin, C-peptide,
proinsulin and adipokines were measured using ELISA kits. Fasting plasma glucose, serum
cholesterol, HDL-cholesterol and triglycerides levels were measured on the ROCHE
MODULAR System. Insulin resistance was calculated using HOMA. Visceral and
subcutaneous fat areas were measured using a 5-level CT-scan. Nutrient intake was assessed
using a validated quantified food frequency questionnaire. Socio-economic status was
estimated from the level of education and the number of selected household amenities. The
data collected from the project was analysed by using SAS System for Windows Release 8.02
SAS Institute Inc., Cary, NC, USA 1999-2001.
V
Results: Results from the study presented in the table below indicate that Indian females were
more insulin resistant and had a worse atherogenic lipid profile than African females
(statistically higher LDL and triglycerides levels). The greater visceral fat mass in the Indian
subjects appears to be associated with triglycerides and correlated with insulin resistance
(r=0.554, p<0.05). This effect was not observed in Africans. African females had a higher
proportion of their energy intake as carbohydrates than Indians (49.3% and. 45.2%,
respectively, p<0.05), whereas Indians had a higher proportion of their total energy intake as
fat than Africans (34.0% and 29.9%, respectively, p<0.05). The level of educational
attainment and possession of household amenities was lower in the African than Indian group,
but this did not significantly influence any of the anthropometric variables.
Conclusions: Visceral fat accumulation was greater in diabetic and lean Indian subjects than
in diabetic and lean African groups, which may explain their higher risk for obesity-related
disorders at lower BMI. Significantly higher HOMA levels in obese Indians and significantly
lower proinsulin/insulin ratio in lean and obese Indian women compared to lean and obese
African women suggests that lean and obese Indians have better beta-cell proinsulinprocessing
efficiency than Africans, probably due to the higher secretory load imposed on beta
cells by the higher level of insulin resistance in the Indian subjects. Triglycerides, one of the
major components in the diagnostic criteria of metabolic syndrome, were significantly
different in the obese group (higher in Indians) and this may lead to the higher prevalence of
CVD in the Indian population. Interethnic differences for leptin levels were observed in the
lean group of women with higher levels in the Indian subjects. When all non-diabetic subjects
were combined serum leptin levels were significantly higher in Indian than African subjects.
This is an intriguing result, since obesity is more common in the African than Indian
populations of South Africa. Caloric intake was higher in lean African than Indian females.
However, the hypothesis that lower leptin levels in lean African females may lead to higher
dietary intake and thus an increased prevalence of obesity in this group must be evaluated in a
longitudinal study of leptin levels and weight gain. The impact of lower socio-economic status
in African than Indian population is not clear; however data from the literature does
demonstrate a negative correlation of obesity prevalence with education and income
Description
PhD (Chemical Pathology),Faculty of Health Sciences, University of the Witwatersrand, 2009
Keywords
hormone studies, metabolic studies