Loading...
“Body fat distribution and cardio-metabolic risk factors in South African men and women”
Author(s)
Davidson, Florence Elizabeth
Date Issued
2020
Type
Thesis
Publisher
Cape Peninsula University of Technology
Abstract
Background: An analysis of pooled population-based studies conducted by the noncommunicable
disease (NCD) risk factor collaboration Africa working group found that
estimates of adiposity and diabetes prevalence in South Africa (SA) were higher than the
global average. Specifically, in the mixed-ancestry population, central obesity rates were high
(87.9% and 42.2% as defined by IDF criteria) in women and men respectively. Furthermore,
the mixed-ancestry population of SA present with a high prevalence of metabolic syndrome
(Mets) (62%) and type-2 diabetes mellitus (28.2%), placing this population at high risk for
cardio-vascular disease (CVD). Visceral adipose tissue (VAT) accumulation is a known risk
factor for cardio-metabolic disease. Typically, waist circumference (WC) is the accepted proxy
of VAT, however, WC and other anthropometry measurements cannot distinguish between
VAT and abdominal subcutaneous adipose tissue (SAT). Imaging modalities such as
computed tomography (CT) and Magnetic Resonance Imaging (MRI) are considered the gold
standard for VAT and abdominal SAT differentiation, but are not readily available in the clinical
setting. Whole body composition studies using dual-energy x-ray absorptiometry (DXA) have
also proved to be relatively accurate in quantifying VAT and abdominal SAT. Furthermore,
DXA is also able to quantify other regional body fat compartments such as gynoid fat
(gluteofemoral), trunk fat, arm and leg fat, all at a substantially lower radiation dose than CT.
Therefore, the overall objective of this thesis was to validate DXA as a method of quantifying
central adiposity, explore the relationship between body fat distribution and cardio-metabolic
risk and determine the ability of DXA compared to anthropometry to identify participants with
MetS.
Methods: The study sample included a total of 46 men and 207 women, all self-described
mixed-ancestry volunteers aged 20 years and older who were part of the Cape Town Vascular
and Metabolic Health (VMH) parent study. Participants underwent anthropometric
measurements, oral glucose tolerance test (OGTT), lipid measurements, DXA and CT scan
examinations. Pearson correlation coefficients and Bland-Altman analysis were used to
determine agreement between DXA and CT measurements. MetS was quantified using the
Joint Interim Statement (JIS) criteria. Robust regression analyses were used to investigate
associations between body fat distribution and cardio-metabolic risk factors. The area under
the curve (AUC) was used to assess the performance of VAT area and anthropometry in
detecting any two components of MetS (excluding WC). Optimal WC and VAT area cut-points
were derived to compare their performance for diagnosing MetS and to compare to
internationally recognised cut-points
Results: The mean age in the 132 women in whom VAT and abdominal SAT were measured
using single slice CT and DXA was 55 and ranged from 45 to 64 years. DXA and CT- derived
measurements of abdominal VAT and SAT were significantly correlated in the overall sample
(r=0.872 and r=0.966, both p<0.001 respectively) and within body mass index (BMI)
categories. In the overall sample, the mean difference (DXA-CT estimates) was 75.3 cm2
(95% CI: 68.8-81.8 cm2, p≤0.0001) for VAT and 54.7 cm2 (47.1-62.3 cm2, p≤0.0001) for SAT.
Within increasing BMI categories, the variance between the two modalities was fixed for VAT
(p=0.359 for obese), whereas the variance for SAT was heteroscedastic (p≤0.0001).
In the cross-sectional study, which included 207 mixed-ancestry SA women and 46 men, the
men had lower body fat mass compared women (26.5 vs. 44.0%), but had more central and
less peripheral fat (both p<0.001). Post-menopausal women had greater % fat mass, (FM),
WC and VAT, and less gynoid % FM than pre-menopausal women (all p≤0.004). After
adjusting for age and sex, VAT accounted for greatest variance in insulin resistance (R2=0.27,
p≤0.01), while trunk %FM and leg %FM accounted for greatest variance in triglyceride
(R2=0.13, p≤0.01) and high-density lipoprotein cholesterol concentrations (R2=0.14, p≤0.01).
The highest AUC for the prediction of MetS in the 204 women was recorded for VAT, followed
by waist-to height-ratio (WHtR) and WC (AUC, 0.767, 0.747 and 0.738 respectively), but these
did not differ significantly (all p>0.192). In contrast, VAT was significantly better than BMI
(p=0.028), hip (p=0.0004) and a body shape index (ABSI) (p<0.0001).
Conclusions: In conclusion, this thesis has for the first time validated DXA as a method of
quantifying visceral adiposity, explored the relationship between body fat distribution and
cardio-metabolic risk and determined the ability of DXA compared to anthropometry to identify
mixed-ancestry participants with MetS. Although we found that DXA overestimated VAT
compared to the gold standard, CT, the variance was fixed in the obese category. These
findings suggest that DXA is a valid measure of VAT and abdominal SAT in the obese group
which is the group most at risk for cardio-metabolic diseases. Furthermore, we have
demonstrated the value of the whole body DXA scan which quantified regional fat depots and
showed that central fat was the most significant correlate of cardio-metabolic risk and lower
body fat was associated with reduced risk. Finally, we have demonstrated in this population
that DXA-derived VAT had no advantage in discriminating MetS than WC, and therefore
confirm that WC can be used as a marker of MetS provided population specific cut-offs are
derived.
disease (NCD) risk factor collaboration Africa working group found that
estimates of adiposity and diabetes prevalence in South Africa (SA) were higher than the
global average. Specifically, in the mixed-ancestry population, central obesity rates were high
(87.9% and 42.2% as defined by IDF criteria) in women and men respectively. Furthermore,
the mixed-ancestry population of SA present with a high prevalence of metabolic syndrome
(Mets) (62%) and type-2 diabetes mellitus (28.2%), placing this population at high risk for
cardio-vascular disease (CVD). Visceral adipose tissue (VAT) accumulation is a known risk
factor for cardio-metabolic disease. Typically, waist circumference (WC) is the accepted proxy
of VAT, however, WC and other anthropometry measurements cannot distinguish between
VAT and abdominal subcutaneous adipose tissue (SAT). Imaging modalities such as
computed tomography (CT) and Magnetic Resonance Imaging (MRI) are considered the gold
standard for VAT and abdominal SAT differentiation, but are not readily available in the clinical
setting. Whole body composition studies using dual-energy x-ray absorptiometry (DXA) have
also proved to be relatively accurate in quantifying VAT and abdominal SAT. Furthermore,
DXA is also able to quantify other regional body fat compartments such as gynoid fat
(gluteofemoral), trunk fat, arm and leg fat, all at a substantially lower radiation dose than CT.
Therefore, the overall objective of this thesis was to validate DXA as a method of quantifying
central adiposity, explore the relationship between body fat distribution and cardio-metabolic
risk and determine the ability of DXA compared to anthropometry to identify participants with
MetS.
Methods: The study sample included a total of 46 men and 207 women, all self-described
mixed-ancestry volunteers aged 20 years and older who were part of the Cape Town Vascular
and Metabolic Health (VMH) parent study. Participants underwent anthropometric
measurements, oral glucose tolerance test (OGTT), lipid measurements, DXA and CT scan
examinations. Pearson correlation coefficients and Bland-Altman analysis were used to
determine agreement between DXA and CT measurements. MetS was quantified using the
Joint Interim Statement (JIS) criteria. Robust regression analyses were used to investigate
associations between body fat distribution and cardio-metabolic risk factors. The area under
the curve (AUC) was used to assess the performance of VAT area and anthropometry in
detecting any two components of MetS (excluding WC). Optimal WC and VAT area cut-points
were derived to compare their performance for diagnosing MetS and to compare to
internationally recognised cut-points
Results: The mean age in the 132 women in whom VAT and abdominal SAT were measured
using single slice CT and DXA was 55 and ranged from 45 to 64 years. DXA and CT- derived
measurements of abdominal VAT and SAT were significantly correlated in the overall sample
(r=0.872 and r=0.966, both p<0.001 respectively) and within body mass index (BMI)
categories. In the overall sample, the mean difference (DXA-CT estimates) was 75.3 cm2
(95% CI: 68.8-81.8 cm2, p≤0.0001) for VAT and 54.7 cm2 (47.1-62.3 cm2, p≤0.0001) for SAT.
Within increasing BMI categories, the variance between the two modalities was fixed for VAT
(p=0.359 for obese), whereas the variance for SAT was heteroscedastic (p≤0.0001).
In the cross-sectional study, which included 207 mixed-ancestry SA women and 46 men, the
men had lower body fat mass compared women (26.5 vs. 44.0%), but had more central and
less peripheral fat (both p<0.001). Post-menopausal women had greater % fat mass, (FM),
WC and VAT, and less gynoid % FM than pre-menopausal women (all p≤0.004). After
adjusting for age and sex, VAT accounted for greatest variance in insulin resistance (R2=0.27,
p≤0.01), while trunk %FM and leg %FM accounted for greatest variance in triglyceride
(R2=0.13, p≤0.01) and high-density lipoprotein cholesterol concentrations (R2=0.14, p≤0.01).
The highest AUC for the prediction of MetS in the 204 women was recorded for VAT, followed
by waist-to height-ratio (WHtR) and WC (AUC, 0.767, 0.747 and 0.738 respectively), but these
did not differ significantly (all p>0.192). In contrast, VAT was significantly better than BMI
(p=0.028), hip (p=0.0004) and a body shape index (ABSI) (p<0.0001).
Conclusions: In conclusion, this thesis has for the first time validated DXA as a method of
quantifying visceral adiposity, explored the relationship between body fat distribution and
cardio-metabolic risk and determined the ability of DXA compared to anthropometry to identify
mixed-ancestry participants with MetS. Although we found that DXA overestimated VAT
compared to the gold standard, CT, the variance was fixed in the obese category. These
findings suggest that DXA is a valid measure of VAT and abdominal SAT in the obese group
which is the group most at risk for cardio-metabolic diseases. Furthermore, we have
demonstrated the value of the whole body DXA scan which quantified regional fat depots and
showed that central fat was the most significant correlate of cardio-metabolic risk and lower
body fat was associated with reduced risk. Finally, we have demonstrated in this population
that DXA-derived VAT had no advantage in discriminating MetS than WC, and therefore
confirm that WC can be used as a marker of MetS provided population specific cut-offs are
derived.
Additional information
Thesis (Doctor of Radiography)--Cape Peninsula University of Technology, 2020
File(s)![Thumbnail Image]()
Loading...
Name
Florence_Davidson_192057383.pdf
Size
3.6 MB
Format
Adobe PDF
Checksum
(MD5):031577f4a23d2d1ff5acada314896699