Motivation
Alcohol consumption is one of the major risk factors of cardiovascular disease (CVD). Excessive
alcohol drinking is the fifth leading cause of death worldwide and the prevalence of alcohol abuse
continues to increase especially in low-income areas of sub-Saharan Africa. The alarming rate of
urbanisation seems to be the driving force for excessive alcohol intake in the developing world. In
addition to its influence on CVD, heavy drinking also results in a number of non-cardiovascular
consequences that include injury, risky sexual behaviour, violent crime and family dysfunction
among black South Africans, contributing to high mortality. Moreover, the highest number of
individuals with human immunodeficiency virus (HIV) infection in South Africa is partly attributable
to high intake of alcohol. HIV remains a major concern in South Africa with significant funding
diverted to address the pandemic. The continued increases in mortality from preventable
outcomes such as stroke, myocardial infarction and renal failure are largely due to urbanisation,
poverty and dysfunctional health systems working with limited budgets. These are some of the
factors requiring in-depth study of the scientific aspects of alcohol intake in South Africa. Although
there is enough evidence that links excessive drinking with hypertension and CVD, the markers of
alcohol intake – self reporting of alcohol, gamma-glutamyltransferase (GGT) and carbohydrate
deficient transferrin – are still not specific enough to isolate other confounding factors in the
association of alcohol intake with CVD. The markers of alcohol that independently predict CVD
and mortality need to be explored. Finally, the severe lack of longitudinal investigations on
alcohol-related hypertension development and total mortality in black South Africans has
compromised the early identification of risk factors associated with these outcomes. This study
will therefore attempt to address the limited availability of longitudinal studies and stimulate
interest for continued investigation.
Aim
The aim of this study was to investigate whether alcohol intake of black South Africans is related
to specific measures of cardiovascular function (change in blood pressure (BP), hypertension
development) and mortality over a period of 5 years.
Methodology
This study was based on the international Prospective Urban and Rural Epidemiology (PURE)
study which includes 26 countries, investigating the cause and development of cardiovascular
risk factors in low, middle and high income countries. This South African leg of the PURE study
started in 2005 in which the baseline data was collected from 2021 black South Africans from
rural and urban areas in Ikageng, Ganyesa and Tlakgameng in the North West Province. Eleven
participants presented with missing data, leaving 2010 participants with complete datasets at
baseline. However, data from these 11 participants was useful, especially for Chapter 4. All
participants gave informed consent and the Ethics committee of the North-West University
(Potchefstroom Campus) approved the study. The follow-up data collection was done in 2010.
General health questionnaires, anthropometric measurements, lipid profiles and cardiovascular
measurements were taken both at baseline and follow-up using appropriate methods. We also
collected blood samples and performed biochemical analyses for lipid markers, liver enzymes,
inflammatory markers and percentage carbohydrate deficient transferrin (%CDT). Finally, we
obtained data on cardiovascular and non-cardiovascular mortality through verbal autopsy and
death certificates.
We made use of analysis of variance (ANOVA) and Chi-square tests to compare means and
proportions, respectively. We used dependent t-tests and the McNemar test to compare baseline
and follow-up variables. Furthermore, we employed single and partial linear regression analyses
to correlate alcohol markers with each other and with the cardiovascular measures. Multiple
regression analyses were used to correlate dependent variables in the study with various
independent variables as required. Finally, we employed multivariable-adjusted Cox regression
analyses to assess the association of the selected alcohol markers with mortality while adjusting
for several independent variables.
Results and Conclusions of each manuscript
- With the first research article (Chapter 4), we aimed to compare self-reported alcohol intake
estimates with GGT and %CDT, considering their relationship with percentage change in
brachial blood pressure (BP) and central systolic blood pressure (cSBP) over 5 years. The
results indicated that only self-reported alcohol intake independently predicted % change in
brachial BP and cSBP. This was not found for the biochemical markers GGT and %CDT.
Self-reported alcohol intake seems to be an important measure to implement by health
systems in low income areas of sub-Saharan Africa, where honest reporting is expected.
- Given the likely presence of high GGT levels in both alcohol consumption and non-alcoholic
fatty liver disease (NAFLD), the second manuscript (Chapter 5) aimed to compare the
cardiovascular and metabolic characteristics of excessive alcohol users and individuals with
suspected NAFLD (confirmed with self-report, GGT and %CDT). We found that different sex
and cardiometabolic profiles characterised excessive alcohol users and individuals suspected
with NAFLD. Lean body mass and male sex were the dominant characteristics in excessive
alcohol use while the NAFLD group had a dysmetabolic profile with obese women making up
the higher proportion of this group. In excessive alcohol users systolic blood pressure and
pulse pressure were independently associated with high-density lipoprotein cholesterol.
Diastolic blood pressure showed a significant correlation with waist circumference. These
disparate profiles may guide healthcare practitioners in primary healthcare clinics to identify
individuals with elevated GGT levels who may suffer from NAFLD or alcohol overuse. These
results emphasise the importance of modifiable risk factors as the main contributors to CVD
and that lifestyle change should be the main focus in developing countries such as South
Africa.
- The third manuscript (Chapter 6) aimed to determine the measure of alcohol intake (selfreported
alcohol intake, GGT and %CDT) that related best with hypertension development,
cardiovascular and all-cause mortality over 5 years in the same population of black South
Africans. We found that GGT was the only independent predictor of hypertension
development, cardiovascular as well as all-cause mortality. Moreover, self-reporting of alcohol
intake predicted incident hypertension, confirming our findings from Chapter 4. The third
marker, %CDT, a highly specific marker of alcohol intake, was not related with any outcome
variable, perhaps due to its low sensitivity. Although self-reported alcohol intake is useful in
low-resource primary healthcare settings, measurement of GGT is encouraged due to its
predictive value for hypertension and mortality. GGT represents alcohol intake, non-alcoholic
steatohepatitis and obesity - all known to have severe cardiovascular consequences.
Discussion and Conclusions
Excessive alcohol intake remains a major concern in the development of hypertension, CVD and
premature death in sub-Saharan Africa. Despite their weaknesses such as bias and nonspecificity,
self-reporting of alcohol consumption and GGT emerged as reliable alcohol markers
that independently predicted 5-year change in BP, hypertension development and total mortality
in this population. Serum %CDT did not show any association with the mentioned cardiovascular
markers. Finally, we were also able to show that black South Africans with suspected NAFLD (i.e.
with high GGT levels who do not consume alcohol) are typically obese women, whereas lean
men were more likely to have high alcohol consumption. Further prospective investigations are
encouraged regarding (a) these mentioned associations, as well as (b) other self-reporting
estimates such as quantity and frequency of drinking and (c) the use of %CDT as a highly
specific marker of alcohol intake. The simultaneous presence of HIV infection in alcohol abuse in
this population also warrants further investigation. / PhD (Physiology), North-West University, Potchefstroom Campus, 2015
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:nwu/oai:dspace.nwu.ac.za:10394/15827 |
| Date | January 2015 |
| Creators | Zatu, Mandlenkosi Caswell |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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