Various dietary risk markers of hypertension in black South Africans : the THUSA and THUSA BANA study

Abstract

Motivation: Hypertension is one of the most important causes of mortality and morbidity in South Africa. An alarming and rapid development of cardiovascular disease is now flowing through developing countries according to the World Health Organisation. There is also very little direct evidence about the determinants of common cardiovascular diseases in large populations such as those of sub-Saharan Africa. Although genetic make-up plays the most important role in the aetiology of hypertension, various studies have shown that certain dietary factors significantly lowers blood pressure and also improve multiple risk factors for patients with cardiovascular disease. There are, however, still some uncertainties, inconsistencies and a lack of data in the literature regarding the effects of most dietary factors on hypertension. Objectives: The main objective of the papers presented in this thesis is to determine which dietary factors could be identified as risk markers that might be associated with the prevalence of hypertension and specific cardiovascular parameters in black South African children. Also, to examine the role of dietary intake in relation to other known hypertension risk factors. Methodology: Manuscripts presented in Chapters 3, 4, and 5 made use of the cross-sectional THUSA SANA project, where black South African children were recruited from randomly selected schools of the North West Province. These children were classified as normotensive and hypertensive after extensive blood pressure measurement. Anthropometric measurements were also taken and dietary intakes were assessed. Significant differences between normotensives and hypertensives were determined by means of independent t-tests. Stepwise regression analyses were done to determine the most significant determinants of hypertension in subject groups. The study presented in Chapter 6 made use of two cross-sectional studies: the THUSA and THUSA BANA studies. The THUSA subjects were apparently healthy black adults from randomly selected sites throughout the North West Province. These participants were subjected to extensive blood pressure measurement, demographic questionnaires, anthropometric measurements and dietary intake assessments. Blood samples were taken for plasma fibrinogen , serum lipids, gamma glutamyl-transferase and insulin analyses. Factor analysis was applied to detect structure in the relationships between variables. All THUSA subjects and all parents of the THUSA SANA subjects gave informed consent and both studies were approved by the Ethics Committee of the Potchefstroom University for CHE. The reader is referred to the abstracts at the beginning of each separate paper in Chapters 3-6 for a description of the subjects, study design and analytical methods used in each paper. Results and conclusions of the individual manuscripts: D Results from the THUSA BANA study showed that dietary factors associated with blood pressure of hypertensive children are remarkably similar to those indicated as deficient intakes in primary school children in South Africa. These dietary factors included: total energy, biotin, folic acid, pantothenic acid, zinc-, iron, magnesium and vitamin A intakes. These dietary factors were the strongest markers for systolic, diastolic and mean blood pressure in black hypertensive children. Dietary results coupled with cardiovascular parameters identified folic acid to be associated with lower blood pressure and biotin intakes to be associated with an increase in systolic and diastolic blood pressure, although intake of both nutrients were deficient. D By following up on the first paper, the aim was focused mainly on the associations of dietary nutrients on cardiovascular parameters of the peripheral vasculature, such as arterial compliance and peripheral vascular resistance, but also on pulse pressure and stroke volume. It were especially macronutrient intakes, such as carbohydrates, protein, saturated fat, and monounsaturated fat, but also magnesium, iron and manganese, that were associated with higher pulse pressure and decreased arterial compliance. Dietary biotin intake showed somewhat contradictory results, namely being associated with increased stroke volume, but also with increased arterial compliance of hypertensive black children - being the only nutrient to be associated with increased arterial compliance.

D Results of the first two papers forced further investigations concerning the association and possible mechanism of action of biotin on the cardiovascular system. The following contradiction still exists: biotin intake is associated with increasing systolic blood pressure, diastolic blood pressure, and stroke volume, but also having the beneficial effect of an association with increased arterial compliance. Whether the insufficient biotin intakes of these children are the cause of this phenomenon is uncertain, but it could be possible that a suboptimal biotin status might accelerate or initiate the development of hypertension in a person who is genetically predisposed to be hypertensive. D Factor analysis extracted five basic patterns of risk factors for hypertension: (1) urban ma/nutritional phenomenon, characterised by urbanisation and high dietary intake of saturated fat, animal protein and sodium; (2) metabolic syndrome X, characterised by old age, insulin resistance, obesity, dyslipidaemia, hypertension, smoking habit and hyperfibrinogenaemia; (3) hypercholesterolaemia and obesity complex, associated with increased aging , obesity, and a simple combination of total cholesterol and LDL; (4) alcoholic hypertriglyceridaemia, associated with age, gamma-glutamyltransferase, plasma triglycerides, smoking habit and central obesity; and (5) central and peripheral cardiovascular effects indicated that hypertension in children is positively associated with cardiac output and negatively with vascular peripheral resistance, while adults showed inverse results. Therefore a shift from a centrally acting mechanism (high cardiac output) to a more peripheral mechanism (high peripheral vascular resistance) in older subjects. Combined discussion: The major contributions of this study lie in the results of biotin intake as marker for hypertension, but also in the results found with specific cardiovascular parameters, such as arterial compliance, stroke volume, peripheral vascular resistance and pulse pressure. Since a recent review of publications stated that there is a paucity of studies examining the effects of multiple nutrients and macronutrients regarding hypertension in children, manuscripts in this thesis have also contributed to this area to a great extent. According to the World Health Organisation evidence is lacking regarding the determinants of hypertension in large populations such as in sub-Saharan Africa. This is addressed by proposing five patterns of hypertension risks that occur in a black South African population. The results of this study are therefore valuable in contributing to the current knowledge regarding hypertension in the black population and it could also give direction for future research in this population. The mechanism of the effect of vitamins on blood pressure and other cardiovascular parameters should be investigated. Results from the four papers led to the formulation of additional recommendations regarding the intake of micronutrients, such as folic acid , biotin, vitamin A, vitamin E, ascorbic acid and macronutrients, such as carbohydrates and saturated fat. Although this study was not designed to determine nutrient needs, the recommendations could possibly prevent the development of hypertension. Recommendations also addressed the correction of a pattern of risk factors rather than a single factor, for example adjusting a person's whole diet, and not only restricting sodium chloride consumption. These recommendations can be used by policy makers and health departments of government, the food industry and health professionals for prevention of cardiovascular diseases.