Introduction

Stroke is second only to coronary heart disease as a leading cause of death throughout the world, and hypertension is known to be the best predictor of stroke. Obviously, recognition and management of hypertension is an imperative if stroke rates are to be reduced. In the United States, 70% of Americans are aware of their hypertension, 59% are being treated for it, and 34% of those have it under control. However, these treatment and control rates are still too low, according to the Chairman of the US Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure.¹

If the situation is unsatisfactory in the USA, how is it in Europe? A new survey has been published that compares the prevalence of hypertension in different countries, and we summarize it here.

Method

Dr Wolf-Maier and colleagues at Loyola University, Michigan, conducted this survey to assess potential differences in the prevalence of hypertension between Europe and North America. They reviewed 8 published national surveys, from the United States, Canada, England, Finland, Germany, Italy, Spain, and Sweden. Representatives of each survey were asked to provide average sex- and age-specific data by 5-year age groups for blood pressure, body mass index (BMI), and counts of hypertensive individuals by treatment and control status.

The number of subjects ranged from 1,823 (Sweden) to 23,129 (Canada). Age ranges were also variable: 35-64 years in the 'narrowest' survey (Spain), and 16-80 in the 'widest' (England). All studies involved at least 2 measurements, using 2-4 cuff sizes, and auscultation of Korotkoff sounds, except in the England survey, where an automatic oscillometric device was used.

Analyses of blood pressures were restricted to subjects 35-74 years of age. Blood pressure, BMI, hypertension prevalence, treatment, and control were calculated for 5-year age-sex groups. (Hypertension was defined as a pressure of 140/90 mm Hg or above.)

Results

There was only slight variability among the European countries for all the year groups, with Germany in the leading position for both systolic and diastolic figures. The European countries all had higher blood pressure measurements than the United States and Canada. Subsequent analyses, therefore, grouped the European countries and the two North American countries. The average blood pressure was 136/83 mm Hg for European countries, and 127/77 mm Hg for North America.

The systolic blood pressure rose in both groups with age, while the diastolic pressure had a much less steep increase with age in the European countries, and actually showed a slight decline after age 50 in North America. Thus the average pressure for 35-39 year-olds was 124/78 mm Hg for Europeans, and 115/75 for North Americans. In the 65-69 year-olds, the difference in average systolic pressures between the regions had increased from 9 mm Hg to 13 mm Hg. By 65, the average pressures were 150/85 (Europe) and 136/74 (North America).²

The prevalence of hypertension (defined as a pressure of 140/90 or above, or treatment with an antihypertensive medication) was 27.6% in North America, compared with 44.2% in Europe (55% in Germany ranging down to 38% in Italy). There was little evidence that BMI values played a role in these differences in hypertension - the average BMI was 27.1 in North America, and 26.9 in Europe.

Hypertension treatment (people with hypertension taking antihypertensives) was reported in 44% of North Americans and in 27% of Europeans. Only 8% of hypertensives in Europe had their condition controlled, compared with 23% in North America.

In another analysis, the prevalence of hypertension was correlated with the incidence of lethal stroke and cardiovascular deaths across the 8 centers. The correlation coefficient for stroke was 0.78 (p=0.028), and for cardiovascular deaths it was 0.44. This is in line with the average mortality rates for stroke in European countries (41.2 per 100,000) and North America (27.6 per 100,000).

Comment

The sampling of national populations and the measurement of blood pressure are difficult to standardize; however, the 'within-country' surveys provide data that are convincing and all point in the same direction, lending credence to this publication.

What are the reasons for the considerable regional differences reported? The authors of the study dismiss genetics, overweight, salt intake, physical exercise, and smoking as differentiating risk factors. They leave the door open for consideration of differing intakes of fruit and vegetables, and alcohol, between Europeans and North Americans. Most likely, they suggest, are the differences in thresholds for treatment and treatment goals. Stricter criteria have been in place in the USA and Canada for several decades, and their implementation has is has probably increased the numbers of treated cases and lowered the mean blood pressure in the older population. Certainly, stroke rates have decreased 'precipitously' in the last 30 years.

It seems clear from what we know today that appropriate control of hypertension is a feasible way to reduce deaths from stroke, and also, to a degree, deaths from other cardiovascular diseases. To achieve this, however, hypertension must first be diagnosed, then treated adequately, and finally followed over the patient's lifetime to ensure that control remains optimal. Sadly, this is not always achieved in North America, or in Europe, where the problem appears to be considerably greater.