The association of body weight, 25-hydroxy vitamin D, sodium intake, physical activity levels and genetic factors with the prevalance of hypertension in a low income, black urban community in Mangaung, Free State, South Africa
English: Hypertension is responsible for a large and increasing proportion of the global disease burden and is becoming increasingly significant in low-income countries. The aim of this study was to determine the association of body weight, 25-hydroxy vitamin D, sodium and potassium intakes, physical activity levels and genetic factors, with the prevalence of hypertension in a low income, black urban community. Various factors influence blood pressure, with especially body weight showing a strong relationship with hypertension. More than half of this study population suffered from hypertension and the majority was overweight or obese, increasing the risk for disease and premature death. All indices of abdominal obesity and body fatness, including BMI, WHtR, adiposity index and waist circumference were significantly related to blood pressure, supporting weight loss as first line intervention for treatment and prevention of hypertension and its accompanying disease burden in this population. Findings also suggest the use of WHtR to screen for hypertension in this population. Higher blood pressure levels are associated with lower levels of vitamin D and low vitamin D levels have been linked to obesity markers. Although the majority of participants in this study were overweight/obese, almost 96% had adequate vitamin D status, despite expected low vitamin D intakes. HIV status did not influence vitamin D status directly, but through BMI. The latitude and high levels of sun exposure could have been responsible for the favorable vitamin D status in the participants. Results confirm the inverse relationship between vitamin D status and hypertension reported by other researchers, but found that this relationship seemed to be dependent on BMI in this study population. Lower sodium intakes accompanied with increased potassium intakes are recommended for the prevention and treatment of hypertension. The blood pressure elevating effect of sodium have been found to be even more profound in black population groups, urging investigation into this possible race-related cause of hypertension. Sodium intakes, as reflected by urinary sodium excretion, were high in this study. Association between sodium intakes and systolic, diastolic and mean arterial pressure were found, with higher sodium intakes being associated with elevated blood pressure levels, indicating the need for dietary sodium reduction strategies to control hypertension in this population. Despite high sodium intakes and low potassium intakes, no association was found between sodium or potassium intakes and the prevalence of hypertension. Increased activity is often advocated as first line treatment in the prevention of hypertension, even when weight loss is not achieved. The majority of participants in this study reported being sedentary or low active. No significant association could be shown between activity level and the prevalence of hypertension. Although HIV status showed a negative correlation with BMI, no correlation could be found between HIV status and activity level. Chronic diseases such as hypertension are likely the result of more than one gene and multiple variants of each gene that interacts with different environmental factors, with each combination making a small contribution to overall homeostasis, function, and therefore health. The high risk polymorphisms of the AGT (M235T and -217); GRK4 (A142V, A486V) and CYP11B2 genes did not seem to play a major genetic role in the high prevalence of hypertension in this population. Only GRK4 (R65L) showed an association with the prevalence of hypertension and a weak negative correlation with mean arterial pressure. Results show that overweight/obesity and excessive sodium intake are the major contributors towards hypertension in this study population. Intervention programmes should focus on preventative strategies that create awareness to promote weight loss and encourage lower salt consumption.
Afrikaans: Hipertensie is verantwoordelik vir ‘n groot en toenemende aandeel in die siektelas wêreldwyd en speel toenemend ‘n belangriker rol in lae inkomste lande. Die doel van hierdie studie was om die verband tussen liggaamsmassa, 25-hidroksie vitamien D, natrium- en kalium inname, fisieke aktiwiteit en genetiese faktore met die voorkoms van hipertensie in ‘n lae inkomste, swart stedelike gemeenskap te vergelyk. Verskeie faktore oefen ‘n invloed op bloeddruk uit, met veral liggaamsmassa wat ‘n sterk verband toon met hipertensie. Meer as die helfde van hierdie hierdie studiepopulasie het aan hipertensie gely en die meerderheid was oorgewig of vetsugtig, wat die risiko vir siekte en voortydige dood verhoog. Alle indikatore van abdominale vetsug en liggaamsvet, insluitende liggaamsmassa indeks, vetindeks en middelomtrek het ‘n betekenisvolle verband met bloeddruk getoon, wat massaverlies as eerste vlak van intervensie ondersteun in die behandeling en voorkoming van hipertensie met die gepaartgaande siektelas in hierdie populasie. Bevindinge ondersteun ook die gebruik van die middel tot lengte verhouding as hulpmiddel om vir hipertensie te sif in hierdie populasie. Hoër bloeddruk word geasossieer met laer vitamien D vlakke en lae vitamien D vlakke word met merkers vir vetsug verbind. Alhoewel die meerderheid deelnemers in hierdie studie oorgewig/vetsugtig was, het bykans 96% voldoende vitamien D status gehad, ten spite van ‘n verwagte lae vitamien D inname. MIV status het nie vitamien D status direk beinvloed nie, maar wel deur liggaamsmassa indeks. Geografiese ligging en hoë vlakke sonblootstelling kon bydra tot die gunstige vitamien D status in die studie se deelnemers. Resultate bevestig die negatiewe verband tussen vitamien D status en hipertensie soos ook deur ander navorsers beskryf, maar hierdie verhouding is waarskynlik van liggaamsmassa indeks afhanklik in hierdie studiegroep. Laer natrium inname tesame met verhoogde kalium innames word aanbeveel vir die voorkoming en behandeling van hipertensie. Daar word beskryf dat die bloeddruk verhogende effek van natrium selfs meer uitgesproke is in swart bevolkingsgroepe, wat ondersoek na hierdie rasverwante oorsaak van hipertensie noodsaak. Natrium inname soos gereflekteer deur urinêre natrium uitskeiding was hoog in hierdie studie. ‘n Verband tussen natrium inname en sistolies, diastoliese en gemiddelde arteriële bloeddruk is gevind, met hoër natrium inname wat met verhoogde bloeddruk verband hou en die behoefte aan natriumbeperkingstrategieë in hierdie populasie aandui ten einde hipertensie te beheer. Ongeag hoë natrium innames en lae kalium innames, is geen verband gevind tussen natrium en kalium inname en die voorkoms van hipertensie. Verhoogde aktiwiteit word dikwels aanbeveel as eerste linie behandeling in die voorkoming van hipertensie, selfs al word massaverlies nie bereik nie. Die meerderheid deelnemers aan hierdie studie het aangedui dat hul onaktief of min aktief is. Geen betekenisvolle verband kon aangedui word tussen aktiwiteit en die voorkoms van hipertensie. Alhoewel MIV status ‘n negatiewe invloed op liggaamsmassa indeks het, kon geen verband tussen MIV status en aktiwiteitsvlak gevind word nie. Chroniese siektes soos hipertensie is waarskynlik die gevolg van meer as een geen en verskeie variante van elke geen se interaksie met verskillende omgewingsfaktore, met elkeen wat ‘n klein bydrae maak tot algemene homeostase, funksie en daarom gesondheid. Die hoë risiko polimorfismes van die AGT (M235T en -217), GRK4 (A142V en A486V) en CYP11B2 gene speel waarskynlik nie ‘n belangrike genetiese rol in die hoë voorkoms van hipertensie in hierdie populasie nie. Slegs GRK4 (R65L) toon ‘n verband met die voorkms van hipertensie en toon ‘n swak negatiewe verband met gemiddelde arteriële bloeddruk. Resultate toon dat oorgewig/vetsug en oormatige natrium inname die belangrikste bydraende faktore tot hipertensie in hierdie studie populasie is. Intervensieprogramme behoort te fokus op voorkomingstrategieë wat bewuswording skep om massaverlies te bevorder en laer soutinname aan te moedig.