The social drift phenomenon : associations between the socio–economic status and cardiovascular disease risk in an African population undergoing a health transition
Background: The global burden of cardiovascular diseases (CVDs) is escalating as part of the rapid health transition that developing countries are experiencing. This increase is associated with shifts in demographics and economics, two of the major factors that affect diet and activity. The term social drift phenomenon (SDP) is used to describe the observations that: in the early stages of the epidemiological and nutrition transitions, it is usually the more affluent, higher socio–economic groups that are affected; in the later stages, it is the poor, lower socio–economic groups that display the consequences of these transitions. Therefore, in developing countries at the beginning of the transition, affluent people have higher prevalence of obesity and increased CVD risk. In developed countries, at much later stages of the transition, obesity and increased CVD risk is more prevalent in the lower socio–economic groups. In South Africa, the Transition and Health during Urbanisation of South Africans (THUSA) study which was done in 1996/1998 indicated that at that time, most of the risk factors for CVD were observed in the more urbanised (richer) subjects. It is not known if this pattern changed in any way due to the present rapid urbanisation of South African blacks. Therefore, in this study we explored the associations between socio–economic status (SES) (measured by level of urbanisation, education and employment) and CVD risk factors in an African population undergoing transition in the North–West Province of South Africa, that were prevalent in 2005 when the baseline data for in the Prospective Urban and Rural Epidemiology (PURE) study were collected. Objectives: The main objective of this dissertation was to examine the SDP in an African population in a nutrition and health transition, by: (i) Reviewing the literature on associations between socio–economic variables and biological health outcomes focusing on CVD risk factors in developed and developing countries; (ii) Analysing the baseline data from the 2005 PURE study to examine the relationships between components of SES, namely level of urbanisation, education and occupation, and nutrition–related CVD risk factors in men and women participating in the PURE study; and (iii) Comparing results on these associations between CVD risk factors and SES from the PURE study with those found in the THUSA study, which was conducted almost 10 years earlier, to examine if social drift in these associations has taken place. Study design: The dissertation is based on a comparison of the CVD risk factors and socio–economic status of the THUSA and PURE studies. Secondary analysis of the baseline cross–sectional epidemiological data from the PURE study was executed. The South African PURE study is part of a 12–year Prospective Urban and Rural Epidemiology study which investigates the health transition in urban and rural subjects in 22 different countries. The main selection criterion was that there should be migration stability within the chosen rural and urban communities. The rural community (A) was identified 450 km west of Potchefstroom on the highway to Botswana. A deep rural community (B), 35 km east from A and only accessible by gravel road, was also included. Both communities are still under tribal law. The urban communities (C and D) were chosen near the University in Potchefstroom. Community C was selected from Ikageng, the established part of the township next to Potchefstroom, and D from the informal settlements surrounding community C. The baseline data for PURE were collected from October to December 2005. A total of 2010 apparently healthy African volunteers (35 years and older), with no reported chronic diseases of lifestyle, tuberculosis (TB) or known human immunodeficiency virus (HIV) were recruited from a sample of 6000 randomly selected households. Methods: A variety of quantitative and qualitative research techniques was used by multidisciplinary teams to collect, measure and interpret data generated from biological samples and validated questionnaires. For this study, the statistical package for social sciences (SPSS) package (version 17.0, SPSS Inc) was used to analyze the data. Means and 95% confidence intervals (CI) of CVD risk and dietary factors were calculated. Participants of both genders were divided into different groups (according to urbanisation, education and employment levels) and compared. Estimated significant differences between rural and urban participants were determined with analysis of variance using the general linear model (GLM), multivariate procedure. Univariate analysis was used to explore further the influence of education on CVD risk factors and dietary intakes. Employment was used as a proxy for income, and pairwise comparisons using GLM, multivariate procedure were done for comparing the three groups (Not answered, employed and not employed). Tests were considered significant at P<0.05. Results: Comparison of urban with rural subjects participating in the PURE study showed that urban men had significantly higher systolic and diastolic blood pressures and lower fibrinogen levels than rural men. In women, systolic and diastolic blood pressure, fasting blood glucose and serum triglycerides were significantly higher in urban subjects whereas fibrinogen levels were significantly lower among urban subjects. After examining the relationship between the level of education and CVD risk factors, we observed that men with higher education levels had significantly higher BMI. In women, serum triglycerides and blood pressure were lower and BMI was significantly higher in the educated subjects. Because it was difficult to distinguish between reported household and individual income levels, we compared CVD risk factors of employed and unemployed subjects. Employed men had significantly higher BMI whereas the unemployed men had significantly higher fasting glucose and fibrinogen levels. Although mean blood pressure of employed men was higher than that of unemployed men, the difference did not reach significance. In women, the only significant difference seen was that employed women had lower high density lipoprotein (HDL) cholesterol, fasting glucose, triglycerides and fibrinogen levels, but they had a significantly higher BMI. Employed women had significantly higher BMI than unemployed women (27.9 [26.3–29.4] versus 26.5 [26.0–27.0] kg/m2). It seems that most of the nutrition related CVD risk factors were still higher in the higher socio–economic group, a situation similar to that reported in the THUSA study. Conclusion: The results of this study showed little evidence of a major social drift in CVD risk factors from subjects participating in the 1996/1998 THUSA study to those in the 2005 PURE study. Most cardiovascular disease risk factors are still higher in the higher SES groups. However, there were some indications (increased fibrinogen in both men and women living in rural areas; higher triglyceride and fasting glucose levels in unemployed women; no significant differences in blood pressure and total cholesterol across different SES groups which existed in the THUSA study) that a social drift in CVD risk factors in our African population is on the way. This means that promotion of healthy, prudent diets and lifestyles should be targeted to Africans from all socio–economic levels for the prevention of CVD.
- Health Sciences