The obese African woman : an endocrinological and cardiovascular investigation
Motivation: The prevalence of obesity is the highest among African women in South Africa. Since obesity is a major cardiovascular risk factor, African women in South Africa could be regarded as a high risk group. However, investigations on obesity-related hypertension are limited in this population group. The associations of body fat distribution and hormones such as leptin and endothelin-1 with cardiovascular function have not yet been determined in these women. It has been determined that endothelin-1 is a role player in the development and/or maintenance of hypertension in various population groups, especially African Americans. Endothelin-1 has also been found to be involved in obesity-related hypertension in non-African population groups. It has been indicated that the obesity-related hormone, leptin, also plays a role in obesity-related hypertension, especially in African Americans. Leptin levels have been found to be higher in obese hypertensive African American women compared to an obese normotensive control group. Since the above-mentioned two hormones playa prominent role in obesity and hypertension in African American and non-African population groups, the lack of data on African women in South Africa serves as motivation to conduct this investigation. Aim: To investigate obesity-related hypertension in African women through the determination of associations between various anthropometric and endocrinological variables with cardiovascular, especially vascular function. Methodology: Manuscripts presented in Chapters 2, 3 and 4 made use of data from the POWIRS (Profiles of Obese Women suffering from the Insulin Resistance Syndrome) I project where African women were selected from a government institution in the North West Province. A group of 98 women were divided into lean normotensive, overweight/obese normotensive and overweight/obese hypertensive groups. Anthropometric and cardiovascular measurements were taken and the lipid profile, leptin and endothelin-1 levels determined. The analysis of covariance (ANCOVA) was used to show significant differences between groups while adjusting for age. Partial correlation coefficients were used to show associations between various variables while adjusting for age. Stepwise linear regression analysis was also used to show associations between variables. The study presented in Chapter 5 made use of both POWIRS I and II, which are studies including Africans and Caucasians, respectively. The methodology of the two studies was the same. All subjects gave informed consent in writing and the Ethics Committee of the North-West University approved the study. The reader is referred to the "Materials and Methods" section of Chapters 2-5 for a more elaborate description of the subjects, study design and analytical methods used in each article. vii Results and conclusions of the individual manuscripts > Results from Chapter 2 showed that the volume loading effect associated with obesity was present in both overweight/obese normotensive and overweight/obese hypertensive groups, however, the accommodating effect observed in the overweight/obese normotensive group was absent in the overweight/obese hypertensive group due to decreased vascular function. This was confirmed by a high pulse pressure. Decreased vascular functioning was associated with the abdominal skin fold. This suggests that abdominal subcutaneous fat may either be a marker of visceral fat, or may in itself contribute to increased cardiovascular risk in Africans. > Results from Chapter 3 showed a negative result. Plasma endothelin-1 levels were similar for the lean normotensive, overweight/obese normotensive and overweight/obese hypertensive groups. After re-dividing the groups into normotensive and hypertensive, and then into lean and overweight/obese, still no differences could be obtained. Additionally, no correlations could be obtained between endothelin-1 and cardiovascular function in any of the groups. These findings suggest that endothelin-1 is not implicated in obesity-related hypertension in African women. > In Chapter 4, leptin levels were elevated in both overweight/obese normotensive and hypertensive groups compared to the lean normotensive group. However, leptin levels did not differ between the two overweight/obese groups. Even though leptin levels were the same, leptin was directly and positively associated with systolic blood pressure and pulse pressure and negatively with arterial compliance only in the overweight/obese hypertensive group, independent of obesity, insulin resistance, hyperinsulinemia and age. > In Chapter 5 the volume loading, as well as the accommodating effect, that is, decreased total peripheral resistance and increased arterial compliance, was present in both African and Caucasian obese groups compared to their lean controls. Even though leptin levels, body mass index and age were similar for both African and Caucasian obese groups, the accommodating effect seemed to be more prominent in the obese Caucasian group, explaining a lower diastolic blood pressure compared to the obese African group. Leptin showed a favourable negative association with diastolic blood pressure and total peripheral resistance in the obese Caucasian group, but not in the obese African group. This may indicate that leptin predominantly exerts pathological influences on obese African women, as determined previously in Chapter 4.
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