The impact of the indices of adiposity on cardiovascular target organ damage in people of African ancestry
Date
2021
Authors
Nkoana, Kgothatso Freddy
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Abstract
The excess body fat in overweight/obese people has serious health implications including
cardiovascular health. Historically, body mass index has been the preferred for the assessment of
adiposity; however, a number of studies have shown that this method has limitations because it
does not distinguish between visceral and subcutaneous fat. Consequently, waist circumference
(WC) is regarded as a more representative index of obesity. Proper assessment of
overweight/obesity is essential especially in populations with a high incidence of obesity as was
the case in the current study our study population which has a 65% incidence of obesity. Previous
studies conducted in this population have mainly used BMI as an index of obesity and therefore
the impact of obesity on cardiovascular target organ changes may not be well understood.
Therefore, in this study we used both indices (BMI and WC) to assess the impact of increased
adiposity on preclinical cardiovascular target organ changes. We recruited 551 individuals of
African ancestry and took anthropometric measurements. Both conventional and 24-hour blood
pressure (BP) were measured. Echocardiography and pulse wave velocity were performed to
measure cardiac and vascular changes, respectively. Additionally, we collected blood samples to
measure serum lipid and hormone (renin, aldosterone, insulin, and leptin) concentrations and 24-
hour urine samples to assess urinary sodium excretion. When participants were stratified according
to BMI status, total cholesterol (TCHOL), triglycerides (TRGL) and LDL-cholesterol (LDL) were
significantly higher in the overweight/obese group compared to the normal BMI individuals. On
the other hand, HDL-cholesterol (HDL) was significantly higher in the normal weight individuals
compared to the overweight/obese group. When WC was used to classify the participants, TCHOL,
TRGL and LDL were significantly higher in the high WC women, while no significant differences
were observed in men. Similar to women, HDL was significantly higher in the normal WC group
compared to the increased WC group. After correcting for covariates, both BMI and WC were
significantly associated with all the lipid profiles in men, while only TRGL and HDL were
associated with the two indices. Overweight/obese participants had significantly high insulin and
leptin levels compared to normal BMI participants. There was no significant difference in renin
and aldosterone concentrations between participants with increased WC and those with normal
WC. When participants were stratified according to BMI, blood pressure was significantly higher
in the total population, men, and women in the overweight/obese group compared to the normal
weight participants. However, when stratification was done according to WC, gender differences
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were observed. Significant differences in blood pressure were only observed in women but not in
men. Only night-time blood pressure was significantly different between the two male groups.
Differences were also observed in the PWV and LVMI between the groups. Individuals with high
BMI and WC had a significantly higher PWV and LVMI compared to the normal weight group.
We then assessed the combined effects of BMI and WC on target organs. Individuals with a normal
BMI and normal WC had the lowest PWV and LVMI, followed by individuals with a normal WC
and an increased BMI. Then individuals with increased BMI and increased WC had the highest
PWV and LVMI. None of the participants with normal BMI had increased WC. These findings
indicate that an increase in BMI and WC is associated with an increase in circulating plasma lipids
in women but not in men. Since a raised BP and plasma lipids is associated with cardiovascular
pathology, increased adiposity is more detrimental to women than men in this population.
Furthermore, our results show an independent relationship between the indices of adiposity (BMI
and WC) and preclinical cardiovascular pathology (increased PWV and LVMI). Even though
general adiposity (BMI) occurs independent of visceral adiposity (WC), visceral adiposity does
not develop independent of general adiposity. Therefore, a reduction of BMI does not necessarily
translate into WC reduction, but WC reduction always results in BMI reduction. This means
reduction of WC is more beneficial than the reduction of BMI in this population.
Description
A dissertation submitted in fulfilment of the requirements for the degree of Master of Science in Medicine to the Faculty of Health Sciences, School of Physiology, University of the Witwatersrand, Johannesburg, 2021