Arterial structure and function in Africans with HIV for > 5 years: longitudinal relationship with endothelial activation and cardiovascular risk markers

OBJECTIVES

We aimed to determine whether people with human immunodeficiency virus (PWHIV) have increased measures of arterial injury [carotid intima-media thickness (cIMT)] and large artery stiffness [carotid-femoral pulse wave velocity (cfPWV)] when compared with their counterparts without HIV, and whether baseline markers of endothelial activation and cardiovascular risk are associated with cIMT and cfPWV after 5 years.

METHODS

We matched 126 PWHIV from North West Province, South Africa, to 126 without HIV according to age, sex and locality. Cardiovascular risk and endothelial function markers [soluble intracellular adhesion molecule (ICAM-1) and soluble vascular cell adhesion molecule (VCAM-1)] were measured at baseline and cIMT and cfPWV at follow-up.

RESULTS

This study included 21.4% men. The use of antiretroviral therapy (ART) increased from 44.1% at baseline to 81.4% at follow-up. At follow-up, cIMT (P = 0.90) and cfPWV (P = 0.35) were similar in the groups. Despite elevated ICAM-1 and VCAM-1 in the PWHIV (all P < 0.001) at baseline, these markers did not associate with cIMT and cfPWV after 5 years. In multivariable-adjusted regression analysis, cIMT associated positively with age (β = 0.31, P = 0.002) and triglyceride: high-density lipoprotein-cholesterol (β = 0.23, P = 0.016) in PWHIV. Mean arterial pressure (MAP) (β = 0.28, P = 0.010) associated positively with cfPWV in the PWHIV. In the people without HIV, sex (β = 0.31, P = 0.004) and glycated haemoglobin (HbA1c) (β = 0.24, P = 0.026) associated with cIMT while age (β = 0.17, P = 0.049), sex (β = 0.29, P = 0.003), MAP (β = 0.31, P = 0.001) and HbA1c (β = 0.21, P = 0.041) associated positively with cfPWV.

CONCLUSIONS

Measures of arterial structure and function were similar in Africans with HIV and their age, sex and locality matched controls. Traditional cardiovascular risk markers rather than elevated endothelial activation at baseline were independently associated with cIMT and cfPWV over 5 years.

HIV treatment is associated with a two-fold higher probability of raised triglycerides: Pooled Analyses in 21 023 individuals in sub-Saharan Africa

BACKGROUND

Anti-retroviral therapy (ART) regimes for HIV are associated with raised levels of circulating triglycerides (TG) in western populations. However, there are limited data on the impact of ART on cardiometabolic risk in sub-Saharan African (SSA) populations.

METHODS

Pooled analyses of 14 studies comprising 21 023 individuals, on whom relevant cardiometabolic risk factors (including TG), HIV and ART status were assessed between 2003 and 2014, in SSA. The association between ART and raised TG (>2.3 mmol/L) was analysed using regression models.

FINDINGS

Among 10 615 individuals, ART was associated with a two-fold higher probability of raised TG (RR 2.05, 95% CI 1.51-2.77, I2=45.2%). The associations between ART and raised blood pressure, glucose, HbA1c, and other lipids were inconsistent across studies.

INTERPRETATION

Evidence from this study confirms the association of ART with raised TG in SSA populations. Given the possible causal effect of raised TG on cardiovascular disease (CVD), the evidence highlights the need for prospective studies to clarify the impact of long term ART on CVD outcomes in SSA.

Deriving an optimal threshold of waist circumference for detecting cardiometabolic risk in sub-Saharan Africa

BACKGROUND

Waist circumference (WC) thresholds derived from western populations continue to be used in sub-Saharan Africa (SSA) despite increasing evidence of ethnic variation in the association between adiposity and cardiometabolic disease and availability of data from African populations. We aimed to derive a SSA-specific optimal WC cut-point for identifying individuals at increased cardiometabolic risk.

METHODS

We used individual level cross-sectional data on 24 181 participants aged ⩾15 years from 17 studies conducted between 1990 and 2014 in eight countries in SSA. Receiver operating characteristic curves were used to derive optimal WC cut-points for detecting the presence of at least two components of metabolic syndrome (MS), excluding WC.

RESULTS

The optimal WC cut-point was 81.2 cm (95% CI 78.5-83.8 cm) and 81.0 cm (95% CI 79.2-82.8 cm) for men and women, respectively, with comparable accuracy in men and women. Sensitivity was higher in women (64%, 95% CI 63-65) than in men (53%, 95% CI 51-55), and increased with the prevalence of obesity. Having WC above the derived cut-point was associated with a twofold probability of having at least two components of MS (age-adjusted odds ratio 2.6, 95% CI 2.4-2.9, for men and 2.2, 95% CI 2.0-2.3, for women).

CONCLUSION

The optimal WC cut-point for identifying men at increased cardiometabolic risk is lower (⩾81.2 cm) than current guidelines (⩾94.0 cm) recommend, and similar to that in women in SSA. Prospective studies are needed to confirm these cut-points based on cardiometabolic outcomes.International Journal of Obesity advance online publication, 31 October 2017; doi:10.1038/ijo.2017.240.

Associations between dietary salt, potassium and blood pressure in South African adults: WHO SAGE Wave 2 Salt & Tobacco

BACKGROUND & AIMS

In June 2016, South Africa implemented legislation mandating maximum sodium levels in a range of processed foods with a goal of reducing population salt intake and disease burden from hypertension. Our aim was to explore the relationship between salt and blood pressure (BP) in a subsample of the World Health Organization Study on global AGEing and adult health (SAGE) Wave 2 before implementation of legislation in South Africa.

METHODS & RESULTS

Blood pressure (BP) was measured in triplicate (n = 2722; median age 56 years; 33% male) and 24-h urine collected in a nested subsample (n = 526) for sodium, potassium and creatinine analysis. Hypertension prevalence was 55% in older adults (50-plus years) and 28% in younger adults (18-49 years). Median salt intake (6.8 g/day) was higher in younger than older adults (8.6 g vs 6.1 g/day; p < 0.001), and in urban compared to rural populations (7.0 g vs 6.0 g/day; p = 0.033). Overall, 69% of participants had salt intakes above 5 g/day. Potassium intakes were generally low (median 35 mmol/day) with significantly lower intakes in rural areas and older adults. Overall, 91% of adults failed to meet the daily potassium recommendation of 90 mmol/d. Salt intakes above 5 g/day, and to a greater extent, a dietary sodium-to-potassium (Na:K) ratio above 2 mmol/mmol, were associated with significantly steeper regression slopes of BP with age.

CONCLUSION

These preliminary results indicate that high dietary Na:K ratio may lead to a greater increase in BP and hypertension risk with age. Interventions to increase potassium intakes alongside sodium reduction initiatives may be warranted.

Asymmetric dimethylarginine and symmetric dimethylarginine prospectively relates to carotid wall thickening in black men: the SABPA study

The relationship of both asymmetric (ADMA) and symmetric (SDMA) dimethylarginine with carotid wall thickness is inconclusive especially among black populations. We aimed to compare carotid intima media thickness (cIMT) and dimethylarginine levels in 75 black and 91 white men at baseline and after a 3-year follow-up, and to investigate associations of percentage change in cIMT with percentage change in dimethylarginine levels (ADMA and SDMA). Plasma levels of ADMA and SDMA were determined with a liquid chromatography mass spectrometry method and B-mode ultrasonography was used to determine the cIMT at baseline and follow-up. In black men, mean cIMT (p = 0.79) and ADMA levels (p = 0.67) remained the same, but SDMA levels were lower (p < 0.001) when comparing baseline and follow-up. In white men, cIMT increased (p < 0.001), but both mean ADMA and SDMA levels decreased (p < 0.001) over time. In black men, percentage change in cIMT was positively associated with percentage change in ADMA (R ² = 0.49; β = 0.46; p < 0.001) and percentage change in SDMA (R ² = 0.46; β = 0.41; p < 0.001). These associations were absent in the white men. Despite lower mean SDMA and similar ADMA and cIMT in black men, percentage change in cIMT was independently associated with percentage change in ADMA and percentage change in SDMA. These results suggest an important role for ADMA and SDMA lowering strategies to delay carotid wall thickening, especially in black populations prone to the development of cardiovascular disease.

Serum selenium levels, the selenoprotein glutathione peroxidase and vascular protection: The SABPA study

Selenium is an important co-factor for the optimal functioning of the antioxidant enzyme, glutathione peroxidase (GPx). Studies investigating the associations of selenium with blood pressure (BP) and hemodynamic measures are sparse. This study investigated whether 24h blood pressure, vascular resistance, arterial compliance and arterial stiffness relate to both serum selenium and GPx activity. In this cross-sectional study selenium levels, GPx activity, ambulatory blood pressure and arterial stiffness of 200 black and 209 white school teachers from South Africa were measured. Serum selenium levels were significantly lower in black compared to white teachers (p<0.001), independent of sex. One in 10 black men and one in five black women were selenium deficient (<8μg/100ml). Only in white men inverse independent associations of 24h systolic BP (β=-0.19; p=0.039) and 24h diastolic BP (β=-0.21; p=0.029) with selenium were found. In the same group, an inverse association between carotid-dorsalis pedis pulse wave velocity (cd-PWV) and GPx activity (β=-0.23; p=0.017) were also found. To conclude, lower serum selenium levels in black populations from the same geographical region as their white counterparts may impact on the loss of the vasculoprotective effects of selenium and selenoproteins such as GPx.

Recent advances in understanding hypertension development in sub-Saharan Africa

Consistent reports indicate that hypertension is a particularly common finding in black populations. Hypertension occurs at younger ages and is often more severe in terms of blood pressure levels and organ damage than in whites, resulting in a higher incidence of cardiovascular disease and mortality. This review provides an outline of recent advances in the pathophysiological understanding of blood pressure elevation and the consequences thereof in black populations in Africa. This is set against the backdrop of populations undergoing demanding and rapid demographic transition, where infection with the human immunodeficiency virus predominates, and where under and over-nutrition coexist. Collectively, recent findings from Africa illustrate an increased lifetime risk to hypertension from foetal life onwards. From young ages black populations display early endothelial dysfunction, increased vascular tone and reactivity, microvascular structural adaptions as well as increased aortic stiffness resulting in elevated central and brachial blood pressures during the day and night, when compared to whites. Together with knowledge on the contributions of sympathetic activation and abnormal renal sodium handling, these pathophysiological adaptations result in subclinical and clinical organ damage at younger ages. This overall enhanced understanding on the determinants of blood pressure elevation in blacks encourages (a) novel approaches to assess and manage hypertension in Africa better, (b) further scientific discovery to develop more effective prevention and treatment strategies and

Cardiac Troponin T as Early Marker of Subclinical Cardiovascular Deterioration in Black Hypertensive Women

BACKGROUND

Hypertensive heart disease is a rising concern, especially among black South African women. As high sensitivity cardiac troponin T (cTnT) is a marker of cardiomyocyte damage, we determined the potential link of (i) systemic endothelial dysfunction (reflected by urinary albumin-to-creatinine ratio), (ii) large artery stiffness, (iii) cardiac volume load (estimated by the N-terminal prohormone B-type natriuretic peptide (Nt-proBNP)), and (iv) ECG left ventricular hypertrophy in post-menopausal black women.

METHODS

In 121 (50 normotensive and 71 hypertensive) black women (mean age: 60.6 years), basic cardiovascular assessments including blood pressure and ECG were performed, along with plasma and urinary biomarkers including cTnT.

RESULTS

The cTnT levels (p=0.049) along with Nt-proBNP (p=0.003), pulse pressure (p<0.0001) and the Cornell product (p=0.030) were higher in hypertensive than normotensive women. Only in hypertensive women, was cTnT independently associated with urinary albumin-to-creatinine ratio (β=0.25; p=0.019), pulse pressure (β=0.31; p=0.019), Nt-proBNP (β=0.47; p<0.0001) and Cornell product (β=0.31; p=0.018). An independent association between albumin-to-creatinine ratio and cTnT was also evident in normotensive women (β=0.34; p=0.037).

CONCLUSION

We found cTnT to be a useful marker in an elderly black population relating to several measures of cardiovascular deterioration - from subclinical endothelial dysfunction to left ventricular hypertrophy.

Quantification of systemic renin-angiotensin system peptides of hypertensive black and white African men established from the RAS-Fingerprint®

Objective:

The objective of this study was to make use of a quantitative and qualitative approach comparing the systemic renin-angiotensin system (RAS) of hypertensive black and white African men by using RAS equilibrium analysis.

Materials and methods:

This sub-study involved 23 black (n = 15) and white (n = 8) hypertensive men aged 39.5–41 years, living in the North West Province of South Africa. The RAS-Fingerprinting was determined with LC-MS/MS quantification of angiotensin peptides. Blood pressure and other variables were determined with known methods.

Results:

The main finding of this study was the significant lower Ang I (<5.0 and 45.1 pg/ml; p = 0.005) and Ang II (15.6 and 123.9 pg/ml; p ⩽ 0.001) encountered in the hypertensive black African men compared to their white counterparts. Levels of Ang 1-5 (downstream metabolite of Ang 1-7) (1.8 and 3.0 pg/ml), were detected in black and white hypertensive men, respectively.

Conclusions:

The observed differences between circulating RAS components, which are reflected via equilibrium angiotensin levels, point to a distinctive molecular regulation of the RAAS in the two study cohorts. The increased peripheral resistance observed in hypertensive black individuals might take over a dominant role in control of blood pressure in this study population. A novel highly sensitive LC-MS/MS method resolved the issue of peptide recovery variations during sample preparation by using internal standards for each individual angiotensin metabolite.

Bioavailable IGF-1 and its Relation to the Metabolic Syndrome in a Bi-Ethnic Population of Men and Women

Insulin-like growth factor 1 (IGF-1), an insulin sensitivity and vasculoprotective factor, associates negatively with the metabolic syndrome. However, IGF-1 is reduced by factors such as inflammation, oxidative stress and liver dysfunction. We investigated the relationship between bioavailable IGF-1 and the number of metabolic syndrome components and determined whether this relationship is independent of inflammation, oxidative stress and gamma glutamyl transferase (γ-GT; a marker of liver dysfunction). This study included 907 black and white participants stratified by sex (aged 43.0±11.8 years). Among them 63 participants had fasting glucose levels of ≥+7.0+mmol/l and/or used diabetes medication. Via standard methods we determined waist circumference, fasting glucose, triglycerides, high-density lipoprotein cholesterol and blood pressure. We also determined high-sensitivity C-reactive protein (CRP), reactive oxygen species (ROS), γ-GT, IGF-1 and insulin-like growth factor binding protein 3 (IGFBP-3). IGF-1/IGFBP-3 was used as an estimate of bioavailable IGF-1. Total IGF-1 was similar between men and women (p=0.10), however, bioavailable IGF-1 was lower in women (p<0.001). In multivariate-adjusted analyses, IGF-1/IGFBP-3 was inversely associated with the number of metabolic syndrome components in both sexes (men: β=- 0.11; p=0.013 and women: β=- 0.17; p=0.003). Upon inclusion of ROS, γ-GT and CRP, significance was lost. In patients without diabetes, the results for men changed marginally, but were consistent for women. We found an inverse association between bioavailable IGF-1 and the number of metabolic syndrome components. But the relationship was dependent on oxidative stress, liver dysfunction and inflammation, suggesting underlying processes by which the metabolic syndrome attenuates IGF-1.

Leptin relates to prolonged cardiovascular recovery after acute stress in Africans: The SABPA study

BACKGROUND AND AIMS

Heightened cardiovascular reactivity and delayed recovery to stress are associated with an increased risk of cardiovascular disease. Africans, who are more prone to develop hypertension, show greater cardiovascular reactivity to stress. However, causal factors underlying individual and ethnic differences in stress reactivity and recovery remain largely unexplored. Leptin, which is known for its sympatho-activating effects, is higher in Africans compared to Caucasians for any given body mass index. We compared how cardiovascular reactivity and recovery relate to leptin in African (n = 200) and Caucasian (n = 209) teachers.

METHODS AND RESULTS

We measured leptin in serum and cardiovascular baseline and reactivity continuously with the Finometer device during the cold pressor test for 1 min, and recovery at intervals of 1, 3 and 5 min. Africans had higher body mass index, leptin and blood pressure (all P < 0.001). After full adjustment in multiple regression analyses, associations were seen mainly at the 5 min recovery interval. In Africans, cardiac output reactivity (β = -0.335; P = 0.0018) and arterial compliance- (β = -0.241; P = 0.048) associated negatively and total peripheral resistance- (β = 0.227; P = 0.047) positively with leptin. In Caucasians, diastolic blood pressure correlated positively with leptin (β = 0.200; P = 0.015).

CONCLUSION

In Africans, higher circulating leptin levels associated with prolonged cardiovascular recovery after exposure to stress which could explain their increased vulnerability to hypertension development.

Endothelial activation and cardiometabolic profiles of treated and never-treated HIV infected Africans

OBJECTIVE

The role the human immunodeficiency virus (HIV) and antiretroviral treatment on endothelial activation, and the subsequent relationship with cardiovascular disease, is not well understood. We investigated endothelial activation, inflammatory and cardiometabolic profiles, and measures of vascular structure and function of 66 antiretroviral treated (ART), 78 never-treated (no-ART) HIV infected and 165 HIV free Africans.

METHODS

Blood samples were obtained for biochemical analysis and blood pressure, pulse wave velocity (PWV) and carotid intima-media thickness (IMT) measurements were performed.

RESULTS

The HIV infection duration was at least five years and the treatment 2.86±0.13 years. The intracellular adhesion molecule (ICAM) and vascular cell adhesion molecule (VCAM) levels were elevated in the HIV infected groups compared to the controls. The odds of higher adhesion molecule levels were increased when HIV infected (especially in the no-ART group); OR no-ART vs. no-HIV: ICAM 3.92 (2.2-7.0); VCAM 16.2 (7.5-35). ICAM and VCAM associated with HIV status and interleukin-6 (IL-6) in the total group (all p<0.01). In both HIV infected groups VCAM associated inversely with CD4 counts (no-ART: β=-0.28, p=0.01; ART: β=-0.22, p=0.07) and TC (no-ART: β=-0.36, p<0.01; ART: β=-0.27, p=0.03). The ART group had an unfavourable lipid profile compared to the no-ART group. The inflammatory markers (C-reactive protein (CRP) and IL-6), PWV and IMT did not differ between the three groups.

CONCLUSION

HIV infected Africans showed endothelial activation when compared to HIV free controls. The endothelial activation was not accompanied by increased inflammation (as measured with CRP and IL-6), arterial stiffness or sub-clinical atherosclerosis.

Leptin is positively associated with blood pressure in african men with a low body mass index: the SAfrEIC study

Severe underweight may be a risk factor for hypertension in developing countries, although the manner whereby this occurs is unknown. Leptin is known to exert both beneficial and detrimental vascular effects, and is predictive of poor cardiovascular outcome at high levels, but also at low levels. We explored the relationship between blood pressure and leptin in black men from South Africa with a body mass index (BMI) in the underweight to normal range. We included 113 African men (BMI≤25 kg/m(2)) and took anthropometric, biochemical and cardiovascular measures. The blood pressure-leptin relationship was then investigated along quintiles of leptin and within BMI stratified median split (20 kg/m(2)) groups. Blood pressure increased across leptin quintiles 1-3 (p for trend≤0.040), whereas no relationship was observed along quintiles 3 to 5 (p for trend≥0.14) (adjusted for age and waist circumference). Blood pressure was similar in the two BMI median split groups (p≥0.083). In the low BMI group only, blood pressure associated positively with leptin following unadjusted, partial, and full adjustment (systolic blood pressure and diastolic blood pressure: R(2)=0.20-0.27, β=0.32-0.34, p≤0.009). Decreasing leptin levels are not likely to contribute to hypertension prevalence in the underweight. Rather, in African men with a BMI≤20 kg/m(2), low leptin levels are positively and independently associated with elevated blood pressure, which is not seen at higher BMI (20-25 kg/m(2)). Our findings suggest a differential concentration dependent vascular effect of leptin in underweight and normal weight African men.

8-Oxo-7,8-dihydro-2'-deoxyguanosine, reactive oxygen species and ambulatory blood pressure in African and Caucasian men: the SABPA study

Various studies indicate a relationship between increased oxidative stress and hypertension, resulting in increased DNA damage and consequent excretion of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG). The aim of this study was to compare urinary 8-oxodG levels in African and Caucasian men and to investigate the association between ambulatory blood pressure (BP) and pulse pressure (PP) with 8-oxodG in these groups. We included 98 African and 92 Caucasian men in the study and determined their ambulatory BP and PP. Biochemical analyses included, urinary 8-oxodG, reactive oxygen species (ROS) (measured as serum peroxides), ferric reducing antioxidant power (FRAP), total glutathione (GSH), glutathione peroxidase (GPx) and glutathione reductase (GR) activity. The African men had significantly higher systolic (SBP) and diastolic blood pressure (DBP) (both p < 0.001). Assessment of the oxidative stress markers indicated significantly lower 8-oxodG levels (p < 0.001) in the African group. The African men also had significantly higher ROS (p = 0.002) with concomitant lower FRAP (p < 0.001), while their GSH levels (p = 0.013) and GR activity (p < 0.001) were significantly higher. Single and partial regression analyses indicated a negative association between urinary 8-oxodG levels with SBP, DBP and PP only in African men. These associations were confirmed in multiple regression analyses (SBP: R(2) = 0.41; β = -0.25; p = 0.002, DBP: R(2) = 0.30; β = -0.21; p = 0.022, PP: R(2) = 0.30; β = -0.19; p = 0.03). Our results revealed significantly lower urinary 8-oxodG in African men, accompanied by a negative association with BP and PP. We propose that this may indicate a dose-response relationship in which increased oxidative stress may play a central role in the up-regulation of antioxidant defence and DNA repair mechanisms.

Evaluation of waist-to-height ratio to predict 5 year cardiometabolic risk in sub-Saharan African adults

BACKGROUND AND AIMS

Simple, low-cost central obesity measures may help identify individuals with increased cardiometabolic disease risk, although it is unclear which measures perform best in African adults. We aimed to: 1) cross-sectionally compare the accuracy of existing waist-to-height ratio (WHtR) and waist circumference (WC) thresholds to identify individuals with hypertension, pre-diabetes, or dyslipidaemia; 2) identify optimal WC and WHtR thresholds to detect CVD risk in this African population; and 3) assess which measure best predicts 5-year CVD risk.

METHODS AND RESULTS

Black South Africans (577 men, 942 women, aged >30years) were recruited by random household selection from four North West Province communities. Demographic and anthropometric measures were taken. Recommended diagnostic thresholds (WC > 80 cm for women, >94 cm for men; WHtR > 0.5) were evaluated to predict blood pressure, fasting blood glucose, lipids, and glycated haemoglobin measured at baseline and 5 year follow up. Women were significantly more overweight than men at baseline (mean body mass index (BMI) women 27.3 ± 7.4 kg/m(2), men 20.9 ± 4.3 kg/m(2)); median WC women 81.9 cm (interquartile range 61-103), men 74.7 cm (63-87 cm), all P < 0.001). In women, both WC and WHtR significantly predicted all cardiometabolic risk factors after 5 years. In men, even after adjusting WC threshold based on ROC analysis, WHtR better predicted overall 5-year risk. Neither measure predicted hypertension in men.

CONCLUSIONS

The WHtR threshold of >0.5 appears to be more consistently supported and may provide a better predictor of future cardiometabolic risk in sub-Saharan Africa.

The link between vascular deterioration and branched chain amino acids in a population with high glycated haemoglobin: the SABPA study

Globally the prevalence of non-communicable diseases, such as hypertension and type 2 diabetes, are escalating. Metabolomic studies indicated that circulating branched chain amino acids (BCAAs) are associated with insulin resistance, coronary artery disease and increased risk for cardiovascular events. We aimed to extend the current understanding of the cardiovascular risk associated with BCAAs. We explored whether BCAAs are related to markers of cardiovascular disease in a bi-ethnic population and whether this relationship was influenced by chronic hyperglycaemia. We included 200 African and 209 Caucasian participants, and determined their ambulatory blood pressure and carotid intima-media thickness (cIMT). We analysed blood samples for glycated haemoglobin (HbA1c) and BCAAs. Participants were stratified into two groups according to their HbA1c value using the median cut-off value of 5.6%. Ambulatory BP, cIMT and BCAAs were significantly higher (all p < 0.001) in the high HbA1c group. Single regression analyses indicated significant positive associations of ambulatory blood pressure and cIMT with BCAAs (all p < 0.05) in both the groups. These associations between ambulatory systolic blood pressure (SBP) (r = 0.16, p = 0.035) and cIMT (r = 0.22, p = 0.004) with BCAAs remained in the high HbA1c group after adjusting for age, gender, ethnicity and body mass index (BMI) and were confirmed in multiple regression analyses (ambulatory SBP: R (2) = 0.17, β = 0.21, p = 0.005 and cIMT: R (2) = 0.30, β = 0.19, p = 0.003). Our results demonstrate that BCAAs are independently related to ambulatory BP and cIMT in individuals with high HbA1c levels and suggest that potential cardiovascular deterioration accompany the rise in BCAAs in conditions of hyperglycaemia.

A comparison of the association between glomerular filtration and L-arginine status in HIV-infected and uninfected African men: the SAfrEIC study

Hypertension, a major risk factor for cardiovascular disease worldwide, is increasing significantly in urbanised South Africans. Impaired glomerular filtration is a potential contributor to hypertension. Although HIV infection is widespread, little is known regarding its contribution to diminished estimated glomerular filtration rate (eGFR) and, in turn, hypertension in Africans. We compared eGFRs and cardiovascular profiles of newly identified HIV infected African men (N=53) not yet undergoing anti-retroviral therapy, and uninfected African men of similar age and anthropometry. The aim of the study was to determine whether eGFR is diminished in treatment naive HIV infected individuals and whether eGFR is associated with a potential modulator of hypertension, namely serum L-arginine. Cardiovascular risk factor profiles of HIV infected and uninfected men were similar. In men with healthy eGFRs >90 ml min(-1) per 1.73 m(2), eGFR was significantly lower with HIV infection (114 (90; 147)) compared with that in uninfected men: (120 (91; 168)), P=0.043. Despite the absence of clinically-diagnosed renal dysfunction, eGFR associated significantly with serum L-arginine only in HIV infected men (R(2)=0.277, β=-0.299, P=0.034), whereas L-arginine did not stay in the model for uninfected men. This difference suggests that the fate of L-arginine as a substrate for nitric oxide generation may be altered in HIV infected individuals. Subsequently this is likely to escalate endothelial dysfunction, contributing to later hypertension and cardiovascular disease. Our findings show that while glomerular filtration rate is not associated with L-arginine in uninfected men, it is diminished and significantly negatively associated with serum L-arginine in HIV infected men.

Alkaline phosphatase and arterial structure and function in hypertensive African men: the SABPA study

BACKGROUND

Vascular calcification is believed to be due to the conversion of vascular smooth muscle cells into osteoblast-like cells and is associated with mortality. Since hypertension and related mortality in Africans is a concern, we investigated associations between a marker of osteoblastic activity, alkaline phosphatase (ALP), and measures of arterial structure and function in hypertensive African men.

METHODS

This study included 79 participants. We conducted 24h ambulatory blood pressure and carotid intima-media thickness (cIMT) measurements. cIMT was obtained with an intra-observer variability of 0.04 mm and the cross-sectional wall area (CSWA) was calculated. ALP was measured in serum.

RESULTS

ALP was within its reference range (101.6 vs. 30.0-120.0 U/L), however cIMT was higher when this group was stratified and compared to gender and age-specific reference values. In univariate and partial regressions, and confirmed with multiple regression analyses, 24h systolic blood pressure (β=0.289, p=0.018), 24h pulse pressure (β=0.387, p=0.002), but not 24h diastolic blood pressure (β=0.073, p=0.58), were positively associated with ALP. In addition, mean cIMT (β=0.322, p=0.006) and CSWA (β=0.285, p=0.013) also correlated positively with ALP after adjusting for significant covariates, and after excluding participants with diabetes, renal dysfunction or a HIV positive status.

CONCLUSION

Serum alkaline phosphatase is adversely associated with measures of arterial structure and function in hypertensive African men.

Double product and end-organ damage in African and Caucasian men: the SABPA study

BACKGROUND

Increasing urbanisation in sub-Saharan African countries is causing a rapid increase in cardiovascular disease. Evidence suggests that Africans have higher blood pressures and a higher prevalence of hypertension-related cardiovascular morbidity and mortality, compared to Caucasians. We investigated double product (systolic blood pressure × heart rate), a substantial measure of cardiac workload, as a possible cardiovascular risk factor in African and Caucasian men.

MATERIAL AND METHODS

The study consisted of 101 urbanised African and 101 Caucasian male school teachers. We measured 24h ambulatory blood pressure and the carotid cross-sectional wall area, and determined left ventricular hypertrophy electrocardiographically by means of the Cornell product. Urinary albumin and creatinine were analysed to obtain the albumin-to-creatinine ratio.

RESULTS

Africans had higher 24h, daytime and nighttime systolic- and diastolic blood pressure, heart rate and resultant double product compared to the Caucasians. In addition, markers of end-organ damage, albumin-to-creatinine ratio and left ventricular hypertrophy were higher in the Africans while cross-sectional wall area did not differ. In Africans after single partial and multiple regression analysis, 24h systolic blood pressure, but not double product or heart rate, correlated positively with markers of end-organ damage (cross-sectional wall area: β=0.398, P=0.005; left ventricular hypertrophy: β=0.455, P<0.001; albumin-to-creatinine ratio: β=0.280, P=0.012). No associations were evident in Caucasian men.

CONCLUSIONS

Double product may not be a good marker of increased cardiovascular risk when compared to systolic blood pressure in African and Caucasian men.

NT-proBNP is associated with fibulin-1 in Africans: the SAfrEIC study

OBJECTIVES

The N-terminal prohormone B-type natriuretic peptide (NT-proBNP) is involved in the regulation of volume load and secreted when systemic cardiac overload occurs. Fibulin-1 on the other hand is a component of many extracellular matrix proteins including those present in atherosclerotic lesions, expressed in elastin-containing fibres of blood vessels, and also in the heart. Due to an alarming prevalence of hypertensive heart disease in black South Africans, we investigated the associations of NT-proBNP with fibulin-1 and markers of arterial stiffness in Africans and Caucasians.

METHODS

We included 231 Africans and 238 Caucasians from South Africa aged 22-77 years. Serum NT-proBNP and fibulin-1 levels were determined, and arterial compliance and pulse wave velocity were measured.

RESULTS

Africans had significantly higher blood pressure and NT-proBNP levels than Caucasians and African men had higher fibulin-1 levels than Caucasian men. In single regression analysis, NT-proBNP was significantly associated with fibulin-1 in African men and Caucasian women. NT-proBNP correlated negatively with arterial compliance in all groups except Caucasian women. After partial adjustments, the association between NT-proBNP and fibulin-1 strengthened in African men only. After full adjustment in multiple regression analysis, the association of NT-proBNP with fibulin-1 was confirmed in African men (R(2)=0.41; β=0.26; p<0.01) and also in younger women (R(2)=0.34; β=0.251; p=0.012).

CONCLUSIONS

Only Africans indicated a significant independent association between NT-proBNP and fibulin-1, suggesting that cardiovascular alterations are already present in this relatively young African population as opposed to Caucasians.

Smoking and vascular dysfunction in Africans and Caucasians from South Africa

Background

Smoking is an important modifiable risk factor for cardiovascular disease, with limited research having been done in Africans. We aimed to determine the association between smoking and measurements of vascular function in Africans and Caucasians.

Methods

We determined anthropometric and cardiovascular variables, serum cotinine and C-reactive protein (CRP) in African and Caucasian participants from South Africa (n = 630).

Results

Africans had significantly lower body mass index (BMI), higher blood pressure and lower socio-economic status (SES) than Caucasians. Only African smokers showed increased arterial stiffness and a significant correlation between smoking and arterial stiffness. African smokers had increased and Caucasian smokers decreased high-density lipoprotein cholesterol (HDL-C) than the non-smokers. After adjusting for confounders, smoking showed few correlations, mainly with heart rate and CRP. In Africans, smoking also correlated positively with HDL-C, with the opposite result in Caucasians.

Conclusion

African smokers had significantly increased arterial stiffness, which was not found in Caucasian smokers. Africans generally demonstrated more associations between smoking and cardiovascular dysfunction than Caucasians.

Ethnic and gender differences regarding the insulin-blood pressure relationship

Ageing is associated with increased insulin and C-peptide levels. Due to a lack of data, our first aim was to establish whether this also holds true for Africans from South Africa. Our second aim was to determine whether an association between insulin/C-peptide levels and blood pressure exist within an African and Caucasian population with increasing age, as well as to establish gender differences. African men and women (N=260) and Caucasian men and women (N=369) were recruited and stratified into age groups (18-35 years, 36-45 years and >45 years). ANCOVAs and partial correlations were performed. Results showed opposing changes in insulin/C-peptide levels of African and Caucasian men with increasing age. Insulin/C-peptide tended to decrease in African men, whereas insulin tended to increase and C-peptide increased significantly (p=0.03) in Caucasian men. Despite similar obesity levels, the oldest African women had significantly lower insulin (p<0.01) and C-peptide (p<0.01) levels compared to their Caucasian counterparts. In conclusion, insulin/C-peptide levels tended to decrease in the African population with increasing age. Despite significantly lower levels of insulin, blood pressure levels of African men seems to be affected more detrimentally compared to their Caucasian counterparts, leaving them more vulnerable for the development of cardiovascular diseases.

Classifying Africans with the metabolic syndrome

This study was aimed to compare prevalences of the metabolic syndrome in Africans using five definitions as proposed by the World Health Organization (WHO), the European Group for the Study of Insulin Resistance (EGIR), the National Cholesterol Education Program Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults [Adult Treatment Panel (ATPIII)], the American College of Endocrinology (ACE), and the International Diabetes Federation (IDF). A further objective was to identify difficulties in classifying Africans with the metabolic syndrome and to suggest specific areas where criteria adjustments for identifying Africans should be made. A case-case-control cross-sectional study involved 102 urban African women. Except for microalbumin data, all data necessary for classification of the metabolic syndrome were collected, including fasting and 2-h glucose and insulin, anthropometric measurements, blood pressure, and lipids. The metabolic syndrome prevalences ranged from 5.4% (EGIR), 15.7% (ATPIII), >or=19.4% (WHO), 24.8% (IDF) to 25.5% (ACE). Only 2.9% (n=3) had a triglyceride level >or=1.69 mmol/l, but 58.8% (n=60) had a HDL-level <1.29 mmol/l, whereas 27% (n=26) were insulin resistant, 22.3% (n=21), had a blood pressure >or=140/90 or used hypertension medication. It seems as if the classification of hypertension, insulin resistance and hyperglycemia might have been adequate, but body composition and dyslipidemia criteria need adjustment for Africans. Since neither definition seems completely suitable for Africans it is suggested that clinical emphasis should rather be on treating any specific cardiovascular disease risk factor that is present, than on diagnosing a patient with the metabolic syndrome.

Von Willebrand factor as marker of vascular function in South African women: the POWIRS Study

BACKGROUND

The increasing prevalence of hypertension and vascular-related morbidity and mortality among Africans emphasizes the need to identify markers for the early detection of vascular disease. Caucasian-based studies demonstrate that the von Willebrand factor (vWf) is a useful marker of vascular dysfunction. We investigated whether associations between this marker and markers of cardiovascular function in Caucasian women are comparable with African women.

METHODS

The study consisted of apparently healthy African (n = 99) and Caucasian (n = 114) women (mean age, 31.0 years), individually matched for age and body mass index. We measured blood pressure and arterial compliance noninvasively, and vWf in serum. We assessed univariate and multivariate-adjusted associations of blood pressure and arterial compliance with vWf.

RESULTS

Although no ethnic difference existed for mean vWf levels, Caucasian and African women showed opposite associations of blood pressure and arterial compliance with vWf after single, partial, and multiple regression analyses. In Caucasians, after full adjustment, systolic (beta = +0.179; P < 0.05) and diastolic (beta = +0.190; P < 0.05) blood pressure correlated positively and arterial compliance negatively (beta = -0.197; P < 0.01) with vWf. Conversely, in Africans, systolic blood pressure correlated weakly, but negatively (beta = -0.168; P = 0.059) with vWf. However, this opposite tendency seemed due to the confounding influence of the depot medroxyprogesterone acetate (DMPA) contraceptive injection and, although >99% power existed, significance disappeared after excluding these subjects (beta = -0.071; P = 0.46).

CONCLUSIONS

Associations of vWf with blood pressure and arterial compliance were not comparable between Caucasian and African women, suggesting that the vWf may not be a useful marker of vascular alterations in African women.

Genetic polymorphisms of beta2- and beta3-adrenergic receptor genes associated with characteristics of the metabolic syndrome in black South African women

BACKGROUND

Genetic variation in the beta2 (ADRB2) and beta3 (ADRB3) adrenergic receptor genes are associated with obesity and insulin resistance. To further elucidate the role of these genes in the pathophysiology of obesity the present study investigated associations between certain polymorphisms in ADRB2 and ADRB3 and parameters of carbohydrate and lipid metabolism in a population of African origin.

MATERIAL AND METHODS

Data of 102 black South African women obtained in the POWIRS (Profile of Obese Women with the Insulin Resistance Syndrome) study were used. Endpoint measurements included several anthropometric variables, resting blood pressure, plasma glucose, insulin, free fatty acids (FFA), ghrelin, leptin and lipids, and insulin resistance as estimated by the homeostasis model assessment (HOMA-IR) index. Polymorphisms were analyzed via PCR based methods.

RESULTS

The percentage body fat was significantly lower (p< or =0.05) and the FFA significantly higher (p< or =0.05) in lean subjects (BMI< or =25 kg/m2) with the Glu27 variant allele compared to subjects with the Gln27 wildtype allele of the ADRB2 gene. In contrast, the variant allele of the ADRB2 gene was significantly positive associated (p< or =0.05) with the HOMA-IR-index in overweight black African women (BMI>25 kg/m2). No significant differences in parameters of the metabolic syndrome were apparent between subjects with the wildtype and variant alleles in the ADRB3 gene.

CONCLUSION

The presence of the Glu27 and Arg64 polymorphisms of the ADRB2 and ADRB3 genes are not directly related to indices of the metabolic syndrome.

Insulin resistance -- the role of ethnicity: evidence from Caucasian and African cohorts

The risk for insulin resistance and subsequent type 2 diabetes varies between different ethnic populations due to differences in the genetic and environmental background. However, obesity and unhealthy lifestyle, crucial determinants of insulin resistance, are on the rise throughout all population groups though the susceptibility towards those factors may differ. Up to the present day it is not clear whether insulin resistance is based on metabolic changes due to lifestyle modifications or rather an ethnic and thus genetic grounded phenomenon. Genetic variations in secretion products of the active fat tissue (adipokines), a different pathophysiology of changes in glucose metabolism and the deep impact of urbanization (environmental factors) are discussed as primary determinants for differences in manifestation of insulin resistance between Caucasian and African populations. These factors may be influenced or modified by a central theme: visceral obesity. This mini review will elaborate on these issues illustrated by observations from Caucasian and African cohorts.

Metabolic syndrome risk in black South African women compared to Caucasian women

Rapid urbanisation has led African women to have an obesity prevalence double than that of Caucasian women, and this also holds true for the stroke prevalence in Africans. The study aimed to compare various metabolic syndrome (MS) criteria of the International Diabetes Federation (IDF) of body mass index and age-matched African (n=102) and Caucasian women (n=115). More Caucasian (30.4%) than African women (24.8%) had MS. Only 48% of African women had waist circumferences (WC) higher than the IDF cutoff, compared to 62.6% of Caucasians. Caucasian women were significantly taller and heavier and had higher triglycerides, plasminogen activator inhibitor-1 activity, and cortisol. African women had significantly higher blood pressure, leptin, fibrinogen and C-reactive protein, and higher odds ratios for having the MS for HDL-cholesterol, blood pressure, and fasting glucose than Caucasians. It is concluded that the IDF WC criterion needs a downward adjustment for African women due to a smaller body size. Lean African women seem to be at higher risk for MS than Caucasians. South Africa needs to stem the increasing rates of type 2 diabetes by decreasing obesity and by education (unschooled African women showed a 4.8 times higher likelihood of having MS than schooled women).

A comparison of uric acid levels in Black African vs Caucasian women from South Africa: the POWIRS study

OBJECTIVES

Elevated levels of uric acid are often associated with cardiometabolic risk factors. The aim of this study was to determine whether uric acid levels differ between African and Caucasian women and whether uric acid is associated with cardiometabolic risk factors within the two ethnic groups.

METHODS

Women from African (N=102) and Caucasian (N=115) descent were recruited and their uric acid levels measured. Anthropometric measurements included height (stature), weight, and waist circumference. Correlations between uric acid and cardiometabolic variables within each ethnic group were also determined.

RESULTS

African women had significantly lower levels of uric acid (P<.01) and significantly higher levels of blood pressure (P=.05) compared to the Caucasian women. There was a significant increase in blood pressure from the lower to higher uric acid tertiles in the African women. Uric acid strongly correlated with waist circumference in both ethnic groups.

CONCLUSIONS

Despite their higher blood pressure, the African women had lower uric acid levels, yet they showed a significant increase in blood pressure from a low uric acid tertile to high uric acid tertile, which was not noticeable in the Caucasian women. A possible explanation is a lower waist circumference in African women compared to Caucasian women.

Inflammation, obesity and cardiovascular function in African and Caucasian women from South Africa: the POWIRS study

The integrated relationship between inflammation, obesity and cardiovascular disease is currently a subject of much research interest. These specific relationships, however, have not been studied in-depth in South African population groups in order to determine the role of ethnicity. It is known that Africans, compared to Caucasians, suffer from a high prevalence of hypertension. It was therefore hypothesized that the levels of inflammatory markers (high-sensitivity C-reactive protein (hsCRP), fibrinogen and leptin) are higher in Africans compared to Caucasians and are notably associated with cardiovascular dysfunction in Africans. Apparently healthy African (N=102) and Caucasian (N=115) women, matched for age and body mass index (BMI), were recruited. Leptin, hsCRP, fibrinogen and lipid levels, waist circumference (WC), BMI, systolic and diastolic blood pressure, cardiac output (CO), total peripheral resistance (TPR) and Windkessel compliance were measured. Results showed that the levels of leptin, hsCRP and fibrinogen were significantly higher (P<0.05) in the African women. The inflammatory markers correlated strongly with cardiovascular parameters, age and obesity (BMI, WC) in both groups, but after adjusting for age and obesity, none of the correlations were significant anymore. Multiple regression analyses (with leptin, hsCRP or fibrinogen as dependent variable) showed that only leptin levels of African women were explained by cardiovascular parameters (BP, TPR and CO). In conclusion, even though African women had significantly higher leptin, hsCRP, fibrinogen and blood pressure levels than Caucasian women, no cardiovascular parameters explained the variation in the inflammatory markers (except for leptin levels of African women).

Leptin is favourably associated with vascular function in obese Caucasians, but not in obese Africans

The comparison of the associations between chronically elevated leptin levels and cardiovascular function in obese Africans and Caucasians has not yet been determined. Therefore, the aim of this study was to compare leptin's associations with cardiovascular function in obese African and obese Caucasian women to determine whether leptin's associations differ between these two groups. This study consisted of two case-case control studies. The first study included a sample of 102 apparently healthy African women and the second, 115 apparently healthy Caucasian women. All lean and obese subjects were selected from each study. The Finometer apparatus was used to obtain a more elaborate cardiovascular profile. Serum leptin levels, insulin levels and the lipid profile were determined. Stroke volume (SV) and cardiac output (CO) were significantly (P< or =0.01) elevated in both obese African and Caucasian groups compared to their lean controls. Total peripheral resistance (TPR) was significantly decreased and arterial compliance (C(W)) significantly increased in both obese African and Caucasian groups. In the obese Caucasian group, diastolic blood pressure (DBP) was significantly (P< or =0.01) lower, SV and C(W) significantly higher (P< or =0.01) and TPR significantly lower compared to the age, body mass index (BMI), and leptin-matched obese African group. After adjusting for age and BMI, leptin correlated negatively with DBP (P< or =0.05; r=-0.33) and TPR (P< or =0.05; r=-0.36) in the obese Caucasian group, but not in the obese African group. Even though leptin levels were similar in obese African and Caucasian women, leptin is favourably associated with vascular function in obese Caucasians, but not in obese Africans.

The influence of testosterone on blood pressure and risk factors for cardiovascular disease in a black South African population

OBJECTIVES

Traditionally high testosterone levels have been thought to have a detrimental effect on lipid profiles. Recently, reports have shown that testosterone has a beneficial effect on lipid profiles. On the other hand, androgens may increase blood pressure via the renin-angiotensin system. The aim of this study was to determine whether the level of testosterone is increased in hypertensive subjects or if other cardiovascular risk factors are altered with increased levels of testosterone in the Black population of South Africa.

METHODS

For this study, 536 male and 666 female Black subjects were included. The subjects were divided into hypertensive and normotensive groups and high and low testosterone groups. Resting blood pressure was recorded with a finger arterial pressure device. Blood sampling and biochemical analyses were done by using standardized methods.

RESULTS

The levels of testosterone in the hypertensive males and females were significantly higher compared to the normotensives. In the male high testosterone group, the level of triglyceride was significantly lower, while the high-density lipoprotein cholesterol level was significantly higher. In the female high testosterone group, systolic blood pressure, cortisol level, and renin activity were significantly higher.

CONCLUSION

In the males, we found beneficial effects of testosterone, which may explain the reported lower incidence of atheroma. However, the testosterone level is also higher with hypertension. The elevated levels of systolic blood pressure and renin activity that were found in the female group with high testosterone levels may be an indication of the role of the renin-angiotensin system in this regard.

Cardiovascular function of African women with different BMIs and blood pressures: the POWIRS study

INTRODUCTION

The aim of this study was to investigate the cardiovascular profiles of a group of African women with different body mass indices and blood pressures.

MATERIALS AND METHODS

The study included a sample of 98 apparently healthy African women. The subjects were divided into three groups: lean normotensive (lean NT), overweight/obese normotensive (OW/OB NT), and overweight/obese hypertensive (OW/OB HT). The Finometer apparatus was used to obtain a more elaborate cardiovascular profile. The lipid profile and subcutaneous fat distributions were also determined.

RESULTS

A positive correlation between blood pressure and increased adiposity was obtained. Cardiac output (CO) was elevated in both OW/OB groups. Arterial compliance (CW) was significantly decreased and total peripheral resistance (TPR) significantly increased in the OW/OB HT group compared to the OW/OB NT group. In the total group, systolic and diastolic blood pressure could be explained best by the abdominal skinfold, which showed a direct positive association with TPR and a negative association with CW . In the OW/OB HT group, the increased TPR could best be explained by the abdominal skinfold.

CONCLUSIONS

In the OW/OB HT group, an increase in CO and decrease in vascular function led to the hypertensivity of this group. This seems to be related to a truncal, especially abdominal subcutaneous fat distribution. The decreased vascular function was reaffirmed by the pulse pressure (PP) exceeding 63 mmHg, indicating that this group was at high risk for the development of further cardiovascular complications. Lack of significant differences between the OW/OB groups for the anthropometric and lipid profile variables and the difference in age may indicate that the younger OW/OB NT group was at high risk and should be followed up in ensuing years.

Plasma endothelin-1 is not increased in overweight/obese hypertensive African women

INTRODUCTION

Endothelin-1 (ET-1) has been found to be higher in hypertensive African Americans and obese hypertensive Caucasians compared to normotensive controls with an enhanced ET-1-dependent vasoconstrictor tone. ET-1 levels and the associations thereof with cardiovascular function in overweight/obese normotensive and hypertensive African women have not been investigated. It is therefore hypothesized that ET-1 levels are elevated in overweight/obese hypertensive African women compared to overweight/obese and lean normotensive controls. Additionally, it is hypothesized that these elevated ET-1 levels are associated with increased total peripheral resistance (TPR) and decreased arterial compliance (C(W)).

MATERIALS AND METHODS

A case-case control study was performed which included 98 African women. The subjects were divided into lean normotensive (lean NT), overweight/obese normotensive (OW/OB NT) and overweight/obese hypertensive (OW/OB HT). The Finometer apparatus was used to obtain a more elaborate cardiovascular profile and plasma immunoreactive ET-1 levels were determined.

RESULTS

ET-1 levels were similar for the three groups. Although a decrease in vascular function was observed in the OW/OB HT group, no correlations were obtained between ET-1 and the cardiovascular profile, before and after adjusting for age.

CONCLUSION

In African women, ET-1 levels did not differ between lean and overweight/obese and normotensive and hypertensive subjects. The lack of significant associations between ET-1 and decreased vascular function in the overweight/obese hypertensive group suggests that ET-1 is not implicated in obesity-related hypertension in African women.

The metabolic syndrome and changing relationship between blood pressure and insulin with age, as observed in Aboriginal and Torres Strait Islander peoples

AIMS

To determine the prevalence of the metabolic syndrome (MS) among Aboriginal and Torres Strait Islander peoples. A further objective was to investigate the relationships between fasting insulin and blood pressure (BP) within these groups with increasing age.

METHODS

A cross-sectional population-based study included 369 Torres Strait Islanders (residing in Torres Strait and Far North Queensland), and 675 Aborigines from central Australia. Data necessary for classification of MS was collected, including fasting and 2-h glucose and insulin, urinary albumin and creatinine, anthropometric measurements, BP, serum lipids.

RESULTS

The ATPIII criteria classified 43% of Torres Strait Islanders and 44% of Aborigines with MS, whereas 32 and 28%, respectively, had the MS according to WHO criteria. Agreement between the two criteria was only modest (kappa coefficient from 0.28 to 0.57). Factor analyses indicated no cluster including both insulin and BP in either population. Significant correlations (P < 0.05) [adjusted for gender, body mass index (BMI) and waist circumference] were observed between BP and fasting insulin: a positive correlation for Torres Strait Islanders aged 15-29 years, and an inverse correlation for Aborigines aged 40 years and older.

CONCLUSION

Torres Strait Islanders and Aborigines had very high prevalences of the MS. Specific population characteristics (high prevalences of central obesity, dyslipidaemia, renal disease) may make the WHO definition preferable to the ATPIII definition in these population groups. The poor agreement between criteria suggests a more precise definition of the metabolic syndrome that is applicable across populations is required. This study showed an inverse relationship with age for the correlation of BP and fasting insulin.

Leptin is independently associated with systolic blood pressure, pulse pressure and arterial compliance in hypertensive African women with increased adiposity: the POWIRS study

High leptin levels are often observed in human obesity and are implicated in obesity-related hypertension. Leptin levels have been found to be higher in hypertensive obese African-American women compared to normotensive African-American women, but a direct association between leptin and blood pressure could not be obtained. Additionally, increased adiposity has been associated with higher aortic stiffness in obese African-American women, but leptin was not included in the study. The effects of leptin on cardiovascular function in African women have not yet been determined. We hypothesised that leptin is directly associated with blood pressure and decreased arterial compliance and that leptin levels are significantly higher in hypertensive overweight/obese African women compared to normotensive overweight/obese African women. A case-case control study was performed which included 98 African women. The subjects were divided into lean normotensive (lean NT), overweight/obese normotensive (OW/OB NT) and overweight/obese hypertensive (OW/OB HT). The Finometer apparatus was used to obtain a more elaborate cardiovascular profile. Serum leptin and insulin levels as well as the HOMA-IR index were determined. Various anthropometric measures were obtained. Leptin levels were elevated (P < or = 0.05) in the OW/OB NT and HT groups compared to the lean NT group, but were similar in the OW/OB NT and HT groups. After adjusting for obesity, insulin resistance, hyperinsulinaemia and age, a direct positive correlation was obtained between leptin and systolic blood pressure (SBP) (P < or = 0.05; r = 0.68) in the OW/OB HT group. Additionally, leptin also correlated negatively with arterial compliance (P< or = 0.05; r = -0.76) and positively with pulse pressure (P < or = 0.05; r = 0.71) in the OW/OB HT group. In conclusion, even though leptin levels were the same in OW/OB HT and NT African women, leptin was directly and positively associated with SBP and pulse pressure and negatively with C(W) only in OW/OB HT African women, independent of obesity, insulin-resistance, hyperinsulinaemia and age.

Substitution of high monounsaturated fatty acid avocado for mixed dietary fats during an energy-restricted diet: effects on weight loss, serum lipids, fibrinogen, and vascular function

OBJECTIVE

First, we wanted to dispel the myth that avocados are fattening and therefore should be avoided in energy-restricted diets. Second, we examined the effects of avocados, a rich source of monounsaturated fatty acids, as part of an energy-restricted diet on weight loss, serum lipids, fibrinogen, and vascular function in overweight and obese subjects.

METHODS

Sixty-one free-living volunteers (13 men and 48 women), with body mass index of 32 +/- 3.9 kg/m(2) (mean +/- standard deviation) participated in this randomized, controlled, parallel study. Subjects were paired and randomly assigned to one of two groups. The experimental group consumed 200 g/d of avocado (30.6 g of fat), which substituted for 30 g of other mixed dietary fats such as margarine or oil, and the control group excluded avocado from their energy-restricted diet for 6 wk. Seven-day isoenergetic menus were planned according to mean energy requirements of both sexes to provide total energy intakes consisting of 30% fat, 55% carbohydrates, and 15% protein. Anthropometric measurements, physical activity, blood pressure, and arterial compliance were measured with standard methods at the beginning and end of the intervention. Fasting blood samples were drawn at the beginning and end of the intervention.

RESULTS

Fifty-five subjects completed the study. The compliance rate to avocado intake in the experimental group was 94.6%. The percentage of plasma oleic acid increased significantly with the consumption of avocado in the experimental group, whereas a decrease was seen in the percentage of myristic acid from baseline to the end of the intervention in both groups but was significant only in the experimental group. Anthropometric measurements (body mass, body mass index, and percentage of body fat) decreased significantly in both groups during the study (P < 0.001), and the change was similar in both groups. Serum lipid concentrations (total cholesterol, low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, and triacylglycerols), fibrinogen, blood pressure, and arterial compliance did not change significantly within or between groups.

CONCLUSION

The consumption of 200 g/d of avocado within an energy-restricted diet does not compromise weight loss when substituted for 30 g of mixed dietary fat. Serum lipid concentrations, plasma fibrinogen, arterial compliance, and systolic and diastolic blood pressures were not affected by weight loss or avocado intake.

Validation of the Finometer device for measurement of blood pressure in black women

The improved Finapres apparatus, known as the Finometer, measures finger blood pressure noninvasively on a beat-to-beat basis and gives waveform measurements similar to intra-arterial recordings. The Finometer measures brachial pressure and corrects for finger pressure accordingly. It also corrects for the hydrostatic height of the finger with respect to the heart level. The objective was to validate the Finometer according to the revised British Hypertension Society (BHS) protocol and the criteria of the Association for the Advancement of Medical Instrumentation (AAMI). We carried out a main validation test using a subject group of 102 black women, which was also divided into smaller groups, namely 24 hypertensives, 25 obese normotensive and 35 lean normotensive women. Finometer and mercury sphygmomanometer blood pressure (BP) measurements were taken early in the morning before breakfast, after the subjects stayed overnight in a research unit. Within the whole subject group, the Finometer satisfied the AAMI criteria for accuracy and achieved an overall A/B grading according to the BHS criteria. The sphygmomanometer measurements were 128+/-20/78+/-12 mmHg compared to 130+/-20/78+/-11 mmHg for the Finometer. The average differences between the mercury sphygmomanometer and Finometer readings for systolic and diastolic BP were, respectively, -1.83+/-6.8 and 0.88+/-7.5. Systolic readings of the Finometer device differed by less than 5 mmHg for 64%, by less than 10 mmHg for 86% and differed by less than 15 mmHg for 96% of all readings. A total of 63% of all diastolic readings of the Finometer by less than 5 mmHg, 85% by less than 10 mmHg and 94% of all readings differed by less than 15 mmHg. On the basis of these results, the Finometer device satisfied the validation criteria of AAMI and received an A/B grading according to the BHS protocol. It can therefore be recommended for measurements in the clinical set-up and for research purposes.

Factor analysis of possible risks for hypertension in a black South African population

To date only a small number of studies have investigated the pattern of associations within a set of hypertension risks. The objective of this study was therefore to examine the interrelation of main hypertension risks in an African population by using factor analysis in order to detect underlying risk patterns. Subjects aged 16-70 years (N=963) were recruited from 37 randomly selected sites throughout the North West Province during 1996-1998. Exclusion criteria were pregnancy, lactation, casual visitors, drunkenness and treatment for chronic diseases, such as hypertension. Subjects with blood pressures exceeding 140/90 mmHg were classified as hypertensive. Children aged 10-15 years were also recruited from 30 randomly selected schools during 2000-2001 (N=694). Children were classified as hypertensive when an average systolic or diastolic blood pressure greater than or equal to the 90th percentile for age and sex was encountered, while correcting for height. The following hypertension risks were measured: urbanisation, obesity, plasma fibrinogen, lipids, insulin, serum gamma glutamyl-transferase, dietary intake, smoking and alcohol consumption. From 23 risks the factor analysis disclosed five factors that explained 56.2% of the variance in the male and 43.5% of the variance in the female group: an urban malnutritional phenomenon, the metabolic syndrome X, a hypercholesterolaemic and obesity complex, an alcoholic hypertriglyceridaemia, and central and peripheral cardiovascular hypertensive effects. In conclusion, South Africans migrating from rural to urban areas adapt to a new lifestyle with numerous risks, resulting in conditions like malnutrition, the metabolic syndrome X, dyslipidaemia, alcoholism, obesity and increased peripheral vascular resistance. For successful prevention of hypertension in a population in transition, a whole risk pattern should be corrected, rather than an individual risk by implementing lifestyle modification programmes.

Dietary markers of hypertension associated with pulse pressure and arterial compliance in black South African children: the THUSA Bana Study

AIM

The aim of the study was to determine which dietary factors contribute to the impairment of arterial compliance, stroke volume, total peripheral resistance and pulse pressure, and could thereby be identified as risk markers in the development of hypertension in black children.

METHODS

Children aged 10 to 15 years were recruited from 30 schools in the North West Province over two years (2000 to 2001). These children comprised 321 black males and 373 females from rural to urbanised communities and 40 male and 79 females subjects with identified high-normal to hypertensive blood pressure. Blood pressure was measured by means of a Finapres apparatus. Through analysis with the Fast Modelflo software program, systemic arterial compliance, pulse pressure, total peripheral resistance and stroke volume were obtained. A 24-hour dietary recall questionnaire and weight and height measurements were taken.

RESULTS

In a stepwise regression analysis the following nutrient were significantly associated (p < or = 0.05) with cardiovascular parmeters of hypertensive subjects: protein, carbohydrates, total fat, polyunsaturated fat, mono-unsaturated fat, saturated fat, fibre, vitamin A, nicotinic acid, biotin, vitamin B(12), ascorbic acid, vitamin E, magnesium, manganese, phoshorus and iron. No significant dietary markers were indicated for the normotensive groups. Dietary intakes of most of these nutrients were below the dietary reference intakes for all groups.

CONCLUSIONS

The results indicate strong associations of protein, polyunsaturated fats, fibre, vitamin A, vitamin C, vitamin E, nicotinic acid, vitamin B(12), biotin and phosphorus with the rate of hypertension in black South African children.

Dietary risk markers that contribute to the aetiology of hypertension in black South African children: the THUSA BANA study

Although clinical hypertension occurs less frequently in children than in adults, ample evidence supports the concept that the roots of essential hypertension extend back to childhood. Since little is available in the literature on causal dietary factors of hypertension in children, this study hypothesised that certain dietary factors can be identified as risk markers that might contribute to the aetiology of hypertension in black children. Children aged 10-15 years were randomly selected from 30 schools in the North West Province from 2000 to 2001. These children comprised 321 black males and 373 females from rural to urbanised communities, of which 40 male and 79 female subjects were identified with high-normal to hypertensive blood pressure. Blood pressure was measured with a Finapres apparatus and data were analysed with the Fast Modelflo software program to provide systolic, diastolic and mean blood pressure. A 24-h dietary recall questionnaire and weight and height measurements were taken. In a stepwise regression analysis, the following variables were significantly associated (P < or = 0.05) with blood pressure parameters of hypertensive males: biotin, folic acid, pantothenic acid, zinc and magnesium. Energy, biotin and vitamin A intakes were significantly associated with blood pressure parameters of hypertensive females. No significant dietary markers were indicated for any of the normotensive groups. Dietary intakes of all of these nutrients were well below the dietary reference intakes. In conclusion, the dietary results coupled with the cardiovascular parameters of this study identified folic acid and biotin as risk markers that could contribute to the aetiology of hypertension in black persons. The low intakes of these nutrients, among others, is a matter of serious concern, as is the increasing tendency towards urbanisation.

Prolactin, testosterone and cortisol as possible markers of changes in cardiovascular function associated with urbanization

People living in large informal settlements in South Africa showed a significant increase in cardio/cerebrovascular disease. This study was undertaken to compare the cardiovascular and endocrine parameters of urbanized and rural black female and males. The hormone levels such as prolactin, cortisol and testosterone may also change with urbanization and could make a contribution to the high rate of hypertension. For this study, 1202 black subjects were selected from 37 randomly selected rural and urbanized settlements. Resting blood pressure was recorded with a Finapres apparatus. Cardiac output, stroke volume, heart rate, total peripheral vascular resistance and compliance had been obtained with the Fast Modelflow software program. An acute laboratory stressor (hand dynamometer exercise) was applied to challenge the cardiovascular system and the measurements were repeated. Blood sampling was done and hormone levels were determined by biochemical analyses. For females, significant lower levels of cortisol were found in the urban strata in comparison with the rural strata. The testosterone levels were significantly lower and the prolactin levels significantly higher for females in the informal settlements compared with the rural strata. It is noticeable that most cardiovascular parameters showed the highest changes with the application of the stressor in the informal settlement strata and the lowest in people living on farms for both male and female. The prolactin levels in males are significantly higher in the informal settlement stratum. Subjects living in informal settlements showed a noticeable endocrine pattern of ongoing stress that can be associated with changes in the cardiovascular parameters with urbanization. This can partly explain the reported high rate of cardio/cerbrovascular disease in black South Africans living in informal settlements.