This week, the Florida Gulf coast played host to the world’s largest meeting of chronic disease epidemiologists. This was the 49th meeting of the American Heart Association Cardiovascular Disease Epidemiology and Prevention Conference and is combined with the Nutrition, Physical Activity and Metabolism conference over 5 days. Although most of the 750 delegates were American, there were also many international attendees, from as far afield as South Korea, with representation from both primary care and hospital physicians, as well as non-medical health professionals, statisticians and research scientists. Listening to the presentations, reading the posters and through many discussions with passionate researchers, one gains a sense of the scale of the global research endeavour which is compiling evidence for the incidence, prevalence, risk factors, determinants, mechanisms and treatment of cardiovascular diseases (CVD). If knowledge is power, then it is epidemiology which continues to power clinical practice and public policy. The highlight was a keynote speech by Professor Graham MacGregor of St George's Hospital, London; a strong advocate for salt reduction over the last 30 years. He described salt as a wonderful public health opportunity because the food industry puts all the salt in food, and so changes in industry practice can change salt intake without the consumers even knowing, with far-reaching implications for both blood pressure and CVD. His compelling evidence included the “evolutionary diet” of Yanamamo Indians who have an average blood pressure of 96/67mmHg, low blood cholesterol, no vascular disease and importantly, no salt or cholesterol in their diet. In contrast, Western populations take in 10-12g of salt every day with high rates of CVD. The WHO calculated that if salt intake were reduced to 6g/day (their recommendation is currently <5g/day), stroke would fall by 24% and coronary heart disease would fall by 18%, with an estimated 2.5 million deaths prevented worldwide. In the UK, largely through the efforts of the Consensus Action on Salt and Health (CASH), chaired by MacGregor, the Department of Health and the Food Standards Agency have initiated a salt reduction programme which is successfully reducing salt in the whole UK population in collaboration with the food industry. Sessions covered a diverse range of topics from the risks of CVD associated with “pre-obesity” and socioeconomic factors, to genome-wide association studies and lifestyle strategies for weight reduction. However, four common themes ran through the conference. Firstly, a new emphasis on risk factors and upstream determinants has stimulated data such as the Global Burden of Disease (GBD) study which estimated how much of CVD worldwide is due to each individual risk factor and therefore, how many deaths can be prevented by modification of that risk factor [1]. MacGregor’s salt data is an example of this type of analysis. Secondly, small modifications of risk factor levels throughout a population tend to have greater effects on public health than a focus on people who are at “high-risk” of disease, as originally proposed by the British epidemiologist, Geoffrey Rose in 1985 [2]. Interestingly, the GBD also showed that up to 50% of the burden of the CVD attributable to a given risk factor is due to levels currently classified as normal. For example, hypertension is generally classified as 140/90mmHg even though epidemiological data have shown that risk increases linearly above a systolic blood pressure of 115mmHg, and so a great deal of the ill-effect of blood pressure is due to this range of blood pressures from 115-140mmHg. Thirdly, as Virchow originally wrote,
“The history of epidemics is the history of disturbances in human culture.” The global epidemic of CVD fits this paradigm and so study of socio-economic determinants and study of CVD in other countries and on a global scale has benefits to research, and most importantly to patient populations. Finally, the experience of salt reduction shows the significant hurdles that exist in translation of good evidence into clinical practice and public policy. Advocacy, sometimes with a single focus (e.g. salt reduction), is a powerful means of jumping this hurdle.

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1. Distribution of major health risks: findings from the Global Burden of Disease study. PLoS Med. 2004 Oct;1(1):e27. Rodgers A, Ezzati M, Vander Hoorn S, Lopez AD, Lin RB, Murray CJ; Comparative Risk Assessment Collaborating Group.
2. Sick Individuals and Sick Populations. International Journal of Epidemiology 1985. 14; 1: 32-38. Rose G.