Title: Explaining population trends in cardiovascular risk: A comparative analysis of health transitions in South Africa and England
Funder: Economic and Social Research Council

Abstract: This study aims to examine notions of epidemiologic transition by identifying and quantifying the drivers of change in chronic disease risk in a middle-income African setting compared to a high-income European setting. Epidemiologic transition theory describes a population shift in disease and mortality from nutritional and infectious disorders to chronic non-communicable diseases (NCDs) such as cardiovascular disease (CVD) over time. The 'transition' is thought to be driven by demographic change (ageing), reductions in nutritional and infectious disease burden, and increases in unhealthy behaviours (poor diet, lack of exercise, smoking) as societies 'advance' economically. The theory was developed based on the socio-economic and epidemiologic changes observed in high-income countries such as England in the first half of the twentieth century, which saw a gradual shift from high and fluctuating mortality at younger ages (mainly due to infectious disease and nutritional deficiencies) to stable low mortality at older ages (largely due to NCDs and injuries). However, empirical research to test the validity of 'epidemiologic transition' in explaining population health change is limited in low- and middle-income countries, particularly on the African continent where infectious diseases have continued to have a significant presence or have resurfaced in recent decades. In addition, consideration of social and environmental determinants of health has been minimal. The study will analyse population trends in total CVD risk, estimated using a validated non-laboratory risk score, as well as trends in selected risk factors, to directly test hypotheses regarding changing patterns of health and disease and their correlates in a country (South Africa) that is considered to be in 'transition' but that has not followed the expected path of declining infectious disease. The estimated trends will be contrasted against recent changes in a country (England) that is believed to have completed the transition and whose experience informed epidemiologic transition theory. Our analysis will employ microdata from nationally-representative repeated cross-sectional surveys conducted in South Africa and England since 1998 in conjunction with relevant local data. The goal is to: a) describe recent trends in CVD risk, b) determine what demographic, behavioural, health, social and environmental factors may explain observed trends and to what extent, and c) determine the amount of population change in CVD risk that is unaccounted for by these factors. The study will assess the relative contributions of factors traditionally implicated in epidemiologic transition theory (ageing, lifestyle, health/medicine, socioeconomic) as well as other factors that have been hypothesised to affect CVD outcomes [psychosocial and environmental factors, infectious disease interactions (eg, HIV/AIDS, tuberculosis)]. We hypothesise that overall CVD risk increased in South Africa during the study period but that this increase is not fully explained by demographic, socioeconomic, behavioural or treatment changes. We hypothesise that social and environmental factors as well as infectious disease interactions may have contributed to some of the patterns in CVD risk. Our study also aims to produce a harmonised dataset compiling national surveys measuring CVD risk factors in South Africa for others to use in future research. We will also make our code for merging the Health Surveys for England available for further use. Our research questions are as follows: 1. What are the population trends in CVD risk in South Africa since its first national health survey in 1998? 2. To what extent are these trends explained by demographic, behavioural, social, environmental, health-related and/or other factors? 3. How do these results compare to those in a high-income country with a different infectious disease profile such as England over the same time period?

Lay abstract: This study uses existing data to identify drivers of recent health transitions in South Africa compared to England. The global burden of non-communicable diseases (NCDs) on health is increasing. Cardiovascular diseases (CVD) in particular are the leading causes of death globally and often share characteristics with many major NCDs. Namely, they tend to increase with age and are influenced by behavioural factors such as diet, exercise and smoking. Risk factors for CVD are routinely measured in population surveys and thus provide an opportunity to study health transitions. Understanding the drivers of health transitions in countries that have not followed expected paths (eg, South Africa) compared to those that exemplified models of 'epidemiologic transition' (eg, England) can generate knowledge on where resources may best be directed to reduce the burden of disease. In the middle-income country of South Africa, CVD is the second leading cause of death after HIV/AIDS and tuberculosis (TB). Moreover, many of the known risk factors for NCDs like CVD are highly prevalent. Rates of hypertension are high, with recent estimates suggesting that over 40% of adults have high blood pressure. Around 60% of women and 30% of men over 15 are overweight in South Africa. In addition, excessive alcohol consumption, a risk factor for many chronic diseases, is high, with over 30% of men aged 15 and older having engaged in heavy episodic drinking within a 30-day period. Nevertheless, infectious diseases such as HIV/AIDS remain the leading cause of death, though many with HIV/AIDS and TB also have NCDs. In high-income countries like England, by contrast, NCDs such as CVD have been the leading causes of death since the mid-1900s. However, CVD and risk factors such as hypertension have been declining in recent decades due to increased prevention and treatment. The major drivers of change in disease burden have been attributed to factors including ageing, improved living standards, urbanisation, lifestyle change, and reduced infectious disease. Together, these changes are often referred to as the epidemiologic transition. However, recent research has questioned whether epidemiologic transition theory accurately describes the experience of many low- and middle-income countries or, in fact, of high-income nations such as England. Furthermore, few studies have empirically tested the relative contributions of demographic, behavioural, health and economic factors to trends in disease burden and risk, particularly on the African continent. In addition, many social and environmental factors are overlooked in this research. To address these gaps, our study will use population measurements of CVD risk derived from surveys in South Africa over nearly 20 years in order to examine whether and to what extent demographic, behavioural, environmental, medical, social and other factors contribute to recent health trends and transitions. We will compare these trends to those occurring in England over the same time period. Thus, this analysis seeks to illuminate the drivers of health transitions in a country which is assumed to still be 'transitioning' to a chronic disease profile but which continues to have a high infectious disease burden (South Africa) as compared to a country which is assumed to have already transitioned following epidemiological transition theory (England). The analysis will employ modelling techniques on pooled cross-sectional data to examine how various factors explain the variation in CVD risk over time in representative population samples from South Africa and England. The results of this analysis may help to identify some of the main contributors to recent changes in CVD risk in South Africa and England. Such information can be used to pinpoint potential areas for intervention, such as social policy and services, thereby helping to set priorities for governmental and nongovernmental action to control the CVD epidemic and improve health.

Research activity codes: 2.4 SURVEILLANCE AND DISTRIBUTION
Health categories: CARDIOVASCULAR