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

[摘要] 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.

[发布机构] University of the Free State