The burden of hypertension and inadequate control in populations

Hypertension is the most prevalent preventable disease affecting 20–50% of the adult population in developed countries [1]. It is a well established risk factor for the development of all clinical manifestations of atherosclerosis [2]. Randomized clinical trials of blood pressure-lowering using different drugs have convincingly shown that the risks associated with rising blood pressure can be substantially reduced, particularly for stroke, but also for coronary heart disease (CHD) and heart failure. Research from the World Health Organization (WHO) suggests that the cardiovascular burden due to raised blood pressure may be greater than previously believed. The WHO Report 2002 estimates that approximately 11% of all disease burden in developed countries is caused by raised blood pressure and that over 50% of CHD and almost 75% of stroke in developed countries is due to systolic blood pressure levels over the theoretical minimum of 115 mmHg [3]. A meta-analysis of 61 prospective studies showed usual blood pressure throughout middle and old age to be strongly and directly related to vascular (and overall) mortality without any evidence of a threshold down to at least 115/75 mmHg [4]. More recently, the INTERHEART case–control study estimated that 22% of heart attacks in Western Europe and 25% of heart attacks in Central and Eastern Europe are due to a history of high blood pressure, and that those with a history of hypertension have just under a two-fold greater risk of a heart attack compared to those with no history of hypertension [5]. The impact of hypertension on the incidence of cardiovascular disease in the general population is best evaluated from the population-attributable risk. The statistics take into account both the prevalence of hypertension and the strength of its impact (risk ratio) on cardiovascular disease. Because of the high prevalence of hypertension in the general population and its risk ratio, approximately 35% of atherosclerotic events are attributable to hypertension. The odds ratio or the relative risk to the individual increases with the severity of hypertension, but the population-attributable risk is greatest for mild hypertension because of its greater prevalence in the general population. Therefore, the burden of cardiovascular disease that arises from hypertension in the general population originates from those with a relatively mild blood pressure elevation [6]. Approximately half of the cardiovascular events in the general population are occurring at blood pressure levels below those recommended for treatment with antihypertensive medications. This indicates a need for vigorous non-pharmacological treatment of individuals with high–normal blood pressure and for initiating drug treatment in the vast majority of patients with mild hypertension based on their total cardiovascular risk. The 2003 European Society of Hypertension–European Society of Cardiology Guidelines for the management of arterial hypertension [7] suggest initiating drug treatment in patients with high–normal blood pressure and high total cardiovascular risk (post-stroke, CHD and diabetic patients). A population-based approach aimed at achieving a downward shift in the distribution of blood pressure in the general population is an important component for any comprehensive plan to prevent hypertension. A small decrement in the distribution of systolic blood pressure is likely to reduce the burden of blood pressure-related illness [8]. An analysis based on the Framingham Heart Study reported that a 2 mmHg reduction in diastolic blood pressure in a white cohort aged 35–64 years would result in a 17% decrease in the prevalence of hypertension, a 14% reduction in the risk of stroke and transient ischemic attacks, and a 6% reduction in the risk of CHD [9]. Only few countries have data available on blood pressure trends and the prevalence of hypertension in the general population. In this issue of the journal, Kastarinen et al. [10] report on five independent cross-sectional surveys conducted in 1982, 1987, 1992, 1997 and 2002 in populations aged 25–64 years resident in the province of North Karelia, Kuopio (Eastern Finland) and Turku-Loimaa region (south-western Finland). The population mean systolic blood pressure in the eastern part of Finland was consistently higher than in the south-western part of the country, both in males and females. The mean systolic blood pressure fell significantly in both sexes in all studied areas when taking into account the entire study period. However, when comparing the last two surveys (1997 and 2002), no further significant decrease in systolic blood pressure was observed in eastern Finland and the mean value even increased in the south-western region. Unfortunately, their study provides no data on body mass index (BMI) or obesity. The prevalence of hypertension decreased significantly over the entire period in both sexes. Despite this favourable trend, Finland continues to have a very high prevalence of hypertension, affecting approximately 50% of middle-aged males and 35% of middle-aged females in 2002. Whenever comparing the population mean blood pressure or prevalence of hypertension, it should be remembered that this is heavily dependent on the population examined, the number of blood pressure readings taken on each occasion, the number of visits and, finally, on the definition of hypertension. From the methodological point of view, our report [11] on five independent cross-sectional population surveys conducted in the Czech Republic in 1985, 1988, 1992, 1997/98 and 2000/01 is fairly comparable with the data presented by Kastarinen et al. [10]. The only difference is that the Finnish data cover a period of 20 years (1982–2002) whereas our five surveys were performed within 15/16 years, showing a significant decrease in mean systolic and diastolic blood pressure and the prevalence of hypertension. The population mean systolic and diastolic blood pressures, as well as the prevalence of hypertension, were consistently higher in the Finnish population. Despite a greater decrease in population, mean blood pressure and the prevalence of hypertension in the Finnish population over the examined period, the latest population mean blood pressure and prevalence of hypertension are still higher in Finland than in the Czech Republic. The Finns have achieved a remarkable decrease in cardiovascular mortality since the early 1970s, and their cardiovascular mortality data are now lower than those for the Czech population [12]. In Belgium, a significant decline in population mean systolic blood pressure values was observed between two surveys (BIRNH and MONICA) conducted in 1980–86 and 1985–92, respectively, for both sexes, being much more favourable for women [13]. The National Health and Examination Survey (NHANES) suggests that the prevalence of hypertension in the USA has declined progressively since 1972 and that blood pressure distribution shifted downward between 1960 and 1988 [14,15]. Unfortunately, the most recent report [16] shows an increase in the prevalence of hypertension in the US population. The increased prevalence of hypertension in the USA between 1988 and 1991 and 1999–2000 appears to be partially related to, but not solely, the increase in BMI. However, some studies have reported evidence to the contrary. German investigators found an increase in systolic blood pressure among women between 1984 and 1990 [17] and this was also true in systolic blood pressure among men and women in Halifax County between 1985 and 1995 [18]. Unfortunately, a large proportion of hypertensives remains untreated or has inadequate blood pressure control on treatment. Hypertension is poorly controlled worldwide [1], with less than 25% of individuals being controlled in developed countries, and less than 10% in developing countries. Hypertension control rates also vary within countries by age, gender, race/ethnicity, socio-economic status, education and quality of health care [19]. Awareness of hypertension has improved in the USA and other Western countries over the past decade, but remains inadequate because only a proportion of those who are aware of their diagnosis are treated, and an even smaller number of those receiving treatment are treated adequately. Unfortunately, however, the most important parameter likely to have an impact on public health is neither the number of those aware of their hypertension nor the number taking steps to improve it but, rather, the percentage whose blood pressure is under control [8]. There is a general trend for females to have a higher awareness of hypertension, to be more frequently treated for this disease and to achieve better blood pressure control [20]. Unfortunately, the gender issue has not been addressed specifically in the paper by Kastarinen et al. [10]. It can be assumed that the decreased population blood pressure and improved control of hypertension have contributed substantially to the significant decrease in stroke and coronary heart disease mortality in Finland.

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