Smoking and vascular dysfunction in African and Caucasian people from South Africa
Zatu, Mandlenkosi Caswell
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Motivation: Smoking is a health risk factor associated with vascular dysfunction worldwide. In South Africa, ethnic differences with regards to smoking exist between the African and Caucasian people. The few available studies in South Africa indicate a higher smoking prevalence in Caucasians over Africans. However, Africans are at a higher risk to develop smoking-related adverse effects on cardiovascular function. Limited data regarding the prevalence of smoking and its associated effects on vascular function in South Africa serves as the motivation for this study. Objective: To determine the prevalence and association of smoking with vascular dysfunction in African and Caucasian people from South Africa. Methodology: The manuscript is presented as Chapter 3 and makes use of the data from the SAfrEIC study (South African study on the influence of Sex, Age, and Ethnicity on Insulin sensitivity and Cardiovascular function). A group of 630 participants (258 Africans and 372 Caucasians), aged between 20 and 70 years were recruited from the urban areas of the North-West Province of South Africa. Anthropometric and cardiovascular measurements were taken and pulse wave velocity (PWV), high sensitivity C-reactive protein (hs-CRP), cotinine and lipid profiles (from blood samples drawn from participants) were determined with appropriate methods. The basic health, demographic and lifestyle questionnaires were completed and each participant was requested to indicate their income per month, duration of smoking and the type of smoke being used . An independent t-test and analysis of covariance (ANCOVA) were used to compare the variables between the two ethnic groups, and between smokers and non-smokers with in each group whilst adjusting for certain confounders. The Chisquare test was used to determine if there were significant differences between categorical variables such as smoking and income. Correlations of smoking with cardiovascular and lipid variables were determined while also adjusting for age, body mass index (BMI) and waist circumference (WC). In addition, PWV measurements were taken while also adjusting for mean arterial pressure (MAP). The study was approved by the Ethics committee of the North-West University and all the subjects gave informed consent in writing. The methods section of the manuscript in chapter 3 has a more detailed description of the experimental procedure used. Results and conclusion: A higher prevalence of smoking was found in Africans over Caucasians. Africans showed a significantly lower weight, BMI, WC, higher blood pressure, favourable lipid profiles and lower socio-economic status than Caucasians. Smokers in each ethnic group revealed significant differences when compared to non-smokers in most of the measured variables. For example, cardiac output and triglycerides were elevated in smokers of both ethnic groups. However, only African smokers showed increased higher density lipoprotein cholesterol (HDL-C) and arterial stiffness than their non-smokers as opposed to lower HDL-C levels in Caucasian smokers than non-smokers. Although correlations of smoking with the measured variables were generally weak, Africans revealed stronger associations than Caucasians, especially before adjustments were made. Metabolic syndrome components, arterial stiffness and peripheral resistance are conditions usually associated with increased cardiovascular risk in Africans, and, together with smoking, these are likely to be the best known risk factors for vascular dysfunction. HDL-C correlated weakly (r-0.13) but significantly (p=0.035) with chronic smoking in Africans - a finding that is not found in the literature. On the other hand, a negative correlation of smoke with HDL-C in Caucasian smokers (chronic: r=-0.12, p=0.026; acute: r=-0.1 0, p=0.052) was found . Cotinine correlated positively with smoking duration, throughout, indicating the persistently high blood levels of nicotine of smokers. Hs-CRP correlated weakly with smoking • duration in Africans (r=0 .13; p=0.038) and Caucasians (r=0.13; p=0.015). Based on the findings of the study, it is concluded that Africans smoke more than the Caucasians. Factors such as socio-economic status and westernized lifestyle (urbanization) seem to play an important role in this regard. In addition, Africans showed more correlations of smoking with other measures of cardiovascular risk than Caucasians, even though these associations were generally weak. This might indicate that smoking could be a larger cardiovascular risk factor in Africans than Caucasians.
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