Selenium and large artery structure and function: a 10-year prospective study.

PURPOSE: Despite selenium's beneficial effects in counteracting oxidative stress, inflammation, and vascular endothelial dysfunction, controversial results exist regarding the long-term associations between selenium and atherosclerosis, arterial stiffness, and hypertension. We investigated in normal and selenium-deficient groups (and the total group), whether serum selenium relates to measures of large artery structure and function over 10 years. METHODS: This longitudinal study included black adults from rural and urban areas in South Africa. Serum selenium and blood pressure were measured at baseline (N = 987). At follow-up, carotid intima media thickness (IMT), cross-sectional wall area (CSWA), carotid-femoral pulse wave velocity (c-fPWV), and blood pressure were measured (N = 718). Selenium deficiency was classified as serum levels < 8 µg/100 ml. RESULTS: In multivariable-adjusted regression analyses performed in the normal selenium group, c-fPWV after 10 years was negatively associated with baseline selenium (ß = - 0.09; p = 0.016). In the normal selenium group, baseline (but not 10 years) blood pressure also associated negatively with baseline selenium (ß = - 0.09; p = 0.007). Both IMT (ß = 0.12; p = 0.001) and CSWA (ß = 0.10; p = 0.003) after 10 years associated positively with baseline selenium in the total, normal, and selenium-deficient groups. CONCLUSION: We found a long-term vascular protective association of selenium on arterial stiffness and blood pressure in Africans with normal selenium levels, supporting the notion that selenium fulfills a vascular protective role. In contrast, we found a potential detrimental association between selenium and carotid wall thickness, particularly evident in individuals within the highest quartile of serum selenium.

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.

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.

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.

Conventional and behavioral risk factors explain differences in sub-clinical vascular disease between black and Caucasian South Africans: the SABPA study.

OBJECTIVES: There is an emerging burden of cardiovascular disease among urban black Africans in South Africa, which has been largely explained by the transition from traditional African lifestyles to more westernized behavior. We examined the role of health behaviors in explaining the excess burden of sub clinical vascular disease seen in black Africans compared to Caucasians. METHODS: This was a cross-sectional study, comprising of urban African teachers (n=192 black, 206 Caucasian) working for one of the four Kenneth Kaunda Education districts in the North West Province, South Africa. Conventional cardiovascular risk factors, 24 h ambulatory blood pressure and objectively measured physical activity (Actical® accelerometers), smoking (confirmed by serum cotinine), and alcohol (serum gamma glutamyl transferase) were assessed. The main outcome was a marker of sub-clinical vascular disease, mean carotid intima media thickness (mCIMT), measured using high resolution ultrasound. RESULTS: Compared with Caucasians, the black Africans demonstrated higher mCIMT (age and sex adjusted ß=0.044, 95% CI, 0.024-0.064 mm). The blacks also had higher 24h systolic and diastolic blood pressure, triglycerides, adiposity, and C-reactive protein. In addition, blacks were less physically active (790.0 kcal/d vs 947.3 kcal/d, p<0.001), more likely to smoke (25% vs 16.3%, p=0.002), and demonstrated higher alcohol abuse (gamma glutamyl transferase, 66.6 µ/L vs 27.2 µ/L, p<0.001) compared with Caucasians. The difference in mCIMT between blacks and Caucasians was attenuated by 34% when conventional risk factors were added to the model and a further 18% when health behaviors were included. CONCLUSION: There is an excess burden of sub clinical vascular disease seen in black Africans compared to Caucasians, which can be largely explained by health behaviors and conventional risk factors.

Should obesity be blamed for the high prevalence rates of hypertension in black South African women?

Hypertension is highly prevalent in South Africa, resulting in high stroke mortality rates. Since obesity is very common among South African women, it is likely that obesity contributes to the hypertension prevalence. The aims were to determine whether black African women have higher blood pressures (BPs) than Caucasian women, and whether obesity is related to their cardiovascular risk. African (N=102) and Caucasian (N=115) women, matched for age and body mass index, were included. Correlations between obesity (total body fat, abdominal obesity and peripheral fat) and cardiovascular risk markers (haemodynamic parameters, lipids, inflammatory markers, prothrombotic factors, adipokines, HOMA-IR (homoeostasis model assessment insulin resistance)) were compared between the ethnic groups (adjusted for age, smoking, alcohol and physical activity). Comparisons between low- and high-BP groups were also made for each ethnic group. Results showed that African women had higher BP (P<0.01) with increased peripheral vascular resistance. Surprisingly, African women showed significantly weaker correlations between obesity measures and cardiovascular risk markers when compared to Caucasian women (specifically systolic BP, arterial resistance, cardiac output, fibrinogen, plasminogen activator inhibitor-1, leptin and resistin). Interestingly, the latter risk markers were also not significantly different between low- and high-BP African groups. African women, however, presented significant correlations of obesity with triglycerides, C-reactive protein and HOMA that were comparable to the Caucasian women. Although urban African women have higher BP than Caucasians, their obesity levels are weakly related to traditional cardiovascular risk factors compared to Caucasian women. The results, however, suggest a link with the development of insulin resistance.

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.