Associations between biological alcohol consumption markers, reported alcohol intakes, and biological health outcomes in an African population in transition
Pisa, Pedro Terrence
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BACKGROUND Alcohol consumption probably plays an important role in the transition associated with urbanisation in developing countries. The World Health Organisation recently stated that alcohol consumption is the fifth leading cause of death worldwide and that intakes are increasing, especially in developing countries. A third of South Africans reported to drink, do so in excess (20 litres of absolute alcohol per drinker per year). The observed pattern of binge drinking is of concern. Binge drinking additionally results in an increased cardiovascular disease risk as well as micronutrient deficiencies, both showing high prevalences in the South African population. More importantly, there is a need to identify and assess with accuracy, high risk drinking in this population. Epidemiological evidence suggests a J or U shaped relationship between alcohol consumption and cardiovascular disease. The South African food based dietary guidelines advise "sensible" drinking, due to the possible cardiovascular protective effects associated with light to moderate alcohol consumption. Additionally, present recommendations for alcohol intake are based mainly on evidence of beneficial effects in populations of developed countries. It is, therefore, important to evaluate the cause and consequences of alcohol intake on both societal and health related issues in an African population, in order to readdress the South African food based dietary guidelines regarding alcohol consumption. Identification and assessment of high risk drinking in a population may be problematic. Therefore, it could be more beneficial to use biological markers of alcohol consumption to verify reported intakes and to identify and assess high risk drinking with better accuracy. Percentage carbohydrate deficient transferrin (%CDT) and gamma glutamyl transferase (GGT) are sensitive to high alcohol consumption and are the most suitable biomarkers available for identifying alcohol abuse in most populations. Biomarkers are defined as indicators of actual or possible changes of systemic, organ, tissue, cellular and sub-cellular structure and functional integrity, which can be used singly or in batteries to monitor health and exposure to compounds in populations and individuals. Development of validated and predictive biomarkers is an essential research objective in medical sciences. Biomarkers must be both biologically and methodologically valid and should reflect a future health outcome at a stage when dietary intervention will be effective. AIMS AND OBJECTIVES The main aim of this thesis is to examine aspects of the role that alcohol plays in the health transition amongst African volunteers in rural and urban areas of the North-West Province of South Africa. Specific objectives were to: 1. Review the literature on alcohol consumption and its consequences, with a focus on the South African situation. 2. Compare self reported alcohol consumption and its association with percentage carbohydrate deficient transferrin (%CDT) and gamma glutamyltransferase (GGT) in a random sample of rural and urban Africans in transition using samples from the PURE study, in an attempt to examine known biological markers for alcohol consumption in this population. 3. Examine the biological health outcomes of alcohol consumption in a random, apparently healthy sample of rural and urban Africans in transition, using the data from the THUSA study. STUDY DESIGN The THUSA study In this cross-sectional, comparative, population-based study 1854 men and women, aged 15 years and older and from five levels of urbanisation (deep rural tribal areas, farms, informal housing areas or squatter camps, established urban townships and 'upper' urban areas) voluntarily participated. This Transition and Health during Urbanisation of South Africans study (THUSA) was conducted between 1996 and 1998. Thirty-seven randomly selected sites were investigated in rural and urban areas covering all districts of the North West Province of South Africa. Pregnant and lactating women as well as subjects taking any form of chronic medication, with body temperatures above 37°C and who were inebriated, were excluded. The PURE study This cross-sectional epidemiological survey was part of the North West Province, South African leg (NWPSA) of the 12-year Prospective Urban and Rural Epidemiology (PURE) study which investigates the health transition in urban and rural subjects. The main selection criterium was that there should be migration stability within the chosen rural and urban communities. The rural community (A) was identified 450 km west of Potchefstroom on the highway to Botswana. A deep rural community (B), 35 km east from A and only accessible by gravel road, was also included. Both communities are still under tribal law. The urban communities (C and D) were chosen near the North-West University (Potchefstroom Campus). Community C was selected from the established part of the Township next to Potchefstroom and D from the informal settlements surrounding community C. The baseline data for NWPSA were collected from October-December 2005. A total of 2010 apparently healthy African volunteers (35 years and older), with no reported chronic diseases of lifestyle, tuberculosis (TB) or known HIV were recruited from a sample of 6000 randomly selected households. METHODS A variety of quantitative and qualitative research techniques was used by a multi-disciplinary team to collect, analyse and interpret data generated from biological samples and questionnaires. Data were analysed using the Statistical Package for Social Sciences (SPSS), version 15 package. Means, medians, standard deviations and 95% confidence intervals were calculated. In the PURE study, data were not normally distributed and non-parametric tests were used to test for significant differences between groups. Wilcoxon signed ranks test and Mann- Whitney/Wilcoxon rank sum tests were used to compare groups. Multivariate regression analysis, stepwise regression methods, Spearman rank-order and partial correlations were used to examine the associations between self-reported alcohol intake and biochemical markers (%CDT and GGT), whilst the latter was used for testing associations after adjustments of possible confounding factors. As for the THUSA study, data that were not normally distributed were logarithmically transformed and non-parametric tests used to test for significant differences between groups and effects of urbanisation. Univariate analysis of variance (ANOVA), post hoc test of least significant differences (LSD), multivariate regression analysis, stepwise regression methods and Spearman rank-order correlations with adjustments for confounding factors were used to examine the relationships between alcohol consumption and biological (health) variables. RESULTS After an extensive in depth literature review on alcohol consumption with a focus the South African situation, three review papers were generated discussing the role alcohol consumption from a molecular to a societal perspective. The THUSA study In this study, 61.5% of the men and 25.2% of the women reported that they consumed alcoholic beverages. Mean alcohol intakes of men (30.2 +/- 47.8 g/day) exceeded the recommend value of 21 g/day. The women had a mean intake of 11.4 +/- 18.8g/day, falling within the 12-15g/day recommendation. Older drinkers (>40 years) and those infected with HIV drank more. Levels of urbanisation had little effect on amounts consumed but sorghum beer was replaced by commercial beer in urban areas. Drinkers had significantly higher HDL-C, serum triglycerides, blood pressure and iron status variables than non-drinkers. When serum ferritin was used to classify subjects into those in negative iron balance (<12µg/L), "normal" balance (12-150µg/L) and positive iron balance (>150µg/L), it became evident that alcohol intake almost doubled the proportion of subjects in positive iron balance (in men: from 25 to 46%; in women from 11 to 23%). The PURE study Of the 716 men and 1192 women, 64% and 33% respectively reported that they consumed alcohol. Mean habitual intakes of self-reported drinking men and women were 29.9 (+/-30.0) and 23.3 (+/-29.1) g of pure alcohol per day. A statistically significant correlation between the two dietary methods (QFFQ and 24 hour recall) was observed, higher than +0.45 in both men and women. Self-reported habitual intakes of the whole group correlated positively and significantly with both %CDT (R=0.32) and GGT (R=0.433). After controlling for confounding factors (body mass index and smoking), these relationships were R= 0.19 and 0.31 respectively. However, 19% (n=45) of the men and 26% (n=184) of the women non-drinkers had elevated GGT while 48% (n=113) and 38% (n=269) of the non-drinking men and women respectively had elevated %CDT levels. DISCUSSION AND CONCLUSIONS These results indicate that despite a significant correlation between reported alcohol intake and GGT and %CDT levels, other factors besides alcohol consumption influenced these two biological markers. Clearly, a more specific marker is needed. The THUSA and PURE studies were done in the same areas of the North West Province from 1996-1998 (THUSA) and in 2005 (PURE). The amounts of alcohol consumption reported by the men drinkers were 30.2 and 29.9g/day, while the proportion of drinkers increased from 61.5% to 64.2% respectively. The women drinkers increased from 25.2% to 33% and the reported amounts shifted from 11.4 to 23.3g/day. These results suggest that the dietary questionnaire used in this population gave similar results for men and indicated a significant increase in alcohol intake amongst the women drinkers (11.4 vs 23.3g/day). It is concluded that both GGT and %CDT could misclassify non-drinking subjects as drinkers in this African population and values of these two markers should be interpreted with care. Additionally, it may be necessary to revise the cut off values for a non drinking African population. Although the beneficial effect of alcohol consumption on HDL-C was observed, the effects on iron status and balance are of concern and should be researched in more detail.
- Health Sciences