Lack of association of glycated haemoglobin with blood pressure and subclinical atherosclerosis in black South Africans: a five-year prospective study

Abstract

Objectives: Hypertension and diabetes are common in rapidly urbanising sub-Saharan African communities. However, lack of longitudinal data in these regions prevents adequate analysis of the link between measures of glycaemia and cardiovascular disease. Therefore, we examined the relationships of fasting glucose and glycated haemoglobin (HbA_1c) with brachial and central blood pressure (BP), and measures of vascular structure and function after five years in black South Africans.
Setting and subjects: Nine hundred and twenty-eight participants were included as part of the Prospective Urban Rural Epidemiological (PURE) study in the North West Province.
Outcome measures: Fasting glucose, HbA_1c and brachial BP at two time points were determined. Central BP, augmentation index (AI) and carotid intima-media thickness (CIMT) were taken at follow-up.
Results: Fasting glucose [4.78 (3.50, 6.30) vs. 5 mmol/l (3.96, 6.42)]; HbA_1c [5.6 (4.9, 6.3) vs. 5.9% (5.2, 6.9) and (37 vs. 41 mmol/mol)]; and BP (134/88.1 vs. 138/89.5 mmHg) increased significantly over five years (p-value < 0.05). However, an association was absent between BP, AI or CIMT and either baseline or the five-year change in glucose or HbA,sub>1c. Multivariate analyses confirmed that neither glucose or HbA_1c predicted changes in BP, CIMT or AI, but factors that did associate significantly were age, male gender, rural location, abdominal obesity, alcohol intake, total cholesterol to high-density lipoprotein ratio, C-reactive protein and antihypertensive medication (R², ranging from 0.24-0.36).
Conclusion: Although both BP and measures of glycaemia increased significantly over five years in black South Africans, glucose was not independently associated with BP or measures of large artery structure or function. We suggest that fasting glucose and HbA_1c below the threshold of diagnosing diabetes should not be used in isolation to predict cardiovascular risk in African individuals.

Keywords: fasting glucose, glycated haemoglobin, ethnicity, atherosclerosis, longitudinal