Ethnic variations and cardiovascular disease
Introduction The im portance of the major risk factors for cardiovascular disease (CVD), such as elevated blood pressure, elevated cholesterol, cigarette smoking and diabetes, has been determ ined from epidem iological studies conducted p rim arily in populations of E uropean origin (L enfan t 1994). However, relatively little a ttention has been focused on the im portance of various risk factors among people of non-European ancestry, who constitute the majority of the world’s population. D eterm ining risk factors among various ethnic populations is im portant to provide us with clues regarding sim ilarities and differences in disease causation and facilitates the development of specific prevention strategies appropriately tailored to distinct ethnic groups. Worldwide patterns of disease and regional differences Globally, the major non-communicable diseases are CVD, cancer and diabetes. In most developed countries CVD rates are declining due to CVD risk factor modification, and improved secondary prevention strategies. By contrast CVD rates are increasing in many developing countries. These increases are due to epidemiological transitions resulting from a decrease in deaths due to acute infectious diseases and an increase in chronic diseases. The World H eart Federation reports that CVD claims approxim ately 15 million lives in the world each year, with over 60 per cent of these deaths occurring in developing countries. By the year 2020, CVD will join infectious diseases as the leading cause of death and disability in these countries. The reasons for this transition include increasing life expectancy secondary to declines in childhood and adult deaths from infections, and an increase in the prevalence of CVD risk factors associated with industrialisation and urbanisation.The burden of CVD varies substantially between geographic regions. Ethnic variations in disease rates are closely tied to geographic patterns of disease (Marmot 1995). An ethnic group refers to a population tha t shares common cultural characteristics, such as language, religion, diet, and has some biological similarity. O ften the first clue that ethnic variations in disease burden exist comes from observed differences in rates and risk factors between
countries. These differences have provided many of the initial hypotheses for the various associations between lifestyle factors and CVD. One of the first epidemiological studies to highlight the variation in coronary heart disease (CHD) ra tes betw een countries was the Seven C ountries Study (M enotti et al. 1993). In this major longitudinal cohort study sixteen cohorts of men aged 49 to 59 years were exam ined and followed for CHD m ortality and total mortality. Large differences in CHD m ortality between countries were observed, with low CHD rates in jap an and the M editerranean countries and high CHD rates in Finland and the U nited States. These differences were in a large part explained by differences in diet, serum cholesterol and blood pressure. The World H ealth Organization (WHO) MONICA project (monitoring of trends and determ inants in cardiovascular disease) is a CVD surveillance project which includes 117 reporting units in forty centres from twenty-six countries (Bothig 1989). These d a ta indicate a g rea te r than fourteenfold difference in CHD m ortality among men and more than an elevenfold difference in CHD m ortality for women exist between countries (Figure 12.1).The massive fluctuations in CVD m ortality which have occurred over relatively short periods of time in selected countries dem onstrate the powerful impact tha t socio-economic changes have on health. For example, the low rate of CVD in Japan is closely tied to the economic prosperity of that country. This is in contrast to the astounding increase in CVD th a t has occurred recently am ong eastern European countries alm ost in parallel with the economic decline and the political instability of this region. These changes have occurred too quickly to be ascribed purely to genetic changes, and they reinforce the fact th a t both genes and environm ental factors m ust be
considered when trying to explain differences in CVD between regions and ethnic groups. Ethnic variations in cardiovascular disease
People of European origin People of European origin include those who originate from northern Europe, such as the Nordic countries and Germany, w estern Europe, including the U nited Kingdom and France, southern Europe, including Spain and Italy, and eastern Europe, which includes the Slavic countries. Disease burden Differences in the age-standardised m ortality rates (ASMRs) vary widely between European populations. D ata from the W HO indicate tha t the CVD m ortality ra te is sixfold higher am ong m en and women in the Russian Federation than among people in France (Figure 12.1). In the 1990s, the ASMR for CHD among men in the Russian Federation was 737 per 100,000 compared with 94 per 100,000 among men in France (World H ealth Statistical Annual 1994). The cerebrovascular disease (GBVD) ASMR was 374 per 100,000 among m en in the Russian Federation compared with 44 per 100,000 in France. Although the CVD m ortality rates are much lower among women, large differences are seen among women between the different countries (Figure 12.1). E astern European countries such as the Russian Federation, Hungary, and the Czech Republic have among the highest CVD rates in the world, which is in marked contrast to most economically stable European countries which have experienced declines in CVD m ortality rates over the past 30 years. Risk factors CVD among European populations is mainly attributable to the major CVD risk factors, namely diets high in saturated fats, elevated serum cholesterol, elevated blood pressure, diabetes and smoking. The epidemic of CVD in the eastern European countries is related to high levels of smoking and excessive alcohol use along with diets high in satu rated fat (M armot 1995). However, CVD, like o ther epidem ics, re la tes closely to social conditions, and its prevalence appears to be more strongly related to the social and cultural conditions of a society than to its genetic make-up. Research to explain why the Italian and French populations rem ain relatively ‘protected’ from CHD has yielded num erous hypotheses. It is likely that dietary differences account for an im portant component of the differences in disease rates. It is believed that the high consumption of oils high in m ono-unsaturated fats, such as olive oil, and antioxidants is responsible for the low rates of CHD in Italy. In
France, the CHD m ortality rate rem ains very low (Artaud-Wild et al. 1993). While this relative protection from CHD has been a ttribu ted by some to a high consumption of alcohol, in particular wine (Criqui and Ringel 1994), others believe the lower rate of CHD m ortality may simply be due to a ‘time-lag’ between increases in consumption of anim al fat and serum cholesterol concentrations (which have occurred only recently) and the expected increase in m ortality (Law 1999). Prevention It is clear that major lifestyle change and vigilant trea tm ent of conventional risk factors result in a decline in CVD rates. In Finland, an impressive 65 per cent reduction in CHD m ortality and stroke was observed between 1972 and 1995. It is estim ated tha t approximately 75 per cent of this decline in CHD m ortality can be explained by a lowering of serum cholesterol by 14 per cent (0.93 mmol/1) in m en and by 18 per cent (1.19 mmol/1) in women, reduction in diastolic blood pressure by 5 per cent (6.6 mmHg) in m en and by 13 per cent (12.7 mmHg) in women and a significant reduction in smoking (by 18 per cent in men) (Vartiainen et al. 1994). In N orth America, a 30 per cent decline in CHD m ortality occurred between 1980 and 1990. O ne-quarter of this decline is attributable to prim ary prevention efforts and about one-third is explained by secondary prevention efforts such as a reduction in serum cholesterol, diastolic blood pressure and smoking. In addition, about 40 per cen t of th is decline is a t t r ib u te d to im proved m edical and surg ical m anagem ent in patients with established coronary disease. More recently, in Poland during the 1990s, a rapid decrease (about 25 per cent) in CHD deaths in early middle age was observed. This decline is a ttribu ted in a large part to m arked dietary changes, including an increased consumption of fruits and vegetables and a reduction in the consumption of anim al fats (Zatonski et al. 1998).