Introduction

Stroke is the second most common cause of death throughout the world, second only to cardiovascular disease (usually a heart attack). And raised blood pressure is the most likely cause of stroke. High blood pressure is therefore an ideal target for improving the health outlook for millions of people.

But how well is high blood pressure diagnosed and treated? In the United States, 70% of Americans are aware they have high blood pressure, 60% are being treated for it, and 35% of those being treated have their blood pressure under control. If you think these rates are too low, how about the situation in other countries?

A new survey has been published that compares European and North American countries, looking at how frequently high blood pressure is found, and how often it is treated with drugs.

What was done

Scientists at Loyola University, Michigan, USA reviewed 8 published blood pressure surveys, one each from the United States, Canada, England, Finland, Germany, Italy, Spain, and Sweden. Blood pressures, body mass index (BMI) as an indicator of overweight, treatments and the success of treatment.

The smallest survey had 1,800 people (Sweden) and the largest 23,129 (Canada). Ages ranged from 16 to 80 years, but the analyses were cut back to just those people between 35 and 74, to allow good comparisons. All reasonable efforts were made to have 'standardized' blood pressure readings - e.g. sitting at rest for 2-3 minutes, various cuff sizes, and so on. Anyone with a blood pressure greater than 140 (systolic) or 90 (diastolic) was labeled as having hypertension, for the purposes of comparison between countries.¹ Results were grouped into 5-year sets (35-39, 40-44, 45-49, and so on).

What was found

There wasn't much variation among the European countries for all the year groups, with people from Germany having the highest average pressures. The European countries all had higher blood pressure measurements than the United States and Canada. All the subsequent analyses, therefore, grouped the European countries together, and compared the average with the USA-plus-Canada group. 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 decrease after age 50 in North America. For example, the average blood 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 average pressures were 150/85 and 136/74 for Europe and North America, respectively.

Over 1 in 4 people in the North America group had high blood pressure (i.e. over 140/90), while in Europe it was almost 1 in 2 people (actually 44%). The highest frequency was in Germany (55%), and the lowest (in Europe) was Italy (38%). Being overweight didn't play a major role in the blood pressure differences between Europe and North America; the average BMIs were 26.9 and 27.1, respectively - virtually the same.

The proportion of people taking antihypertensive drugs was almost double in the North American group than in the Europeans - 44% vs. 27%. Only 8% of those taking medication for high blood pressure in Europe had their condition under control, compared with 23% in North America.

Finally, the scientists looked for a link between the occurrence of high blood pressure and the occurrence of fatal stroke and cardiac deaths in all 8 survey centers. They found a strong link between high blood pressure and stroke, and a weaker link with cardiac deaths. The average mortality rate for stroke in European countries is 41.2 per 100,000 and in North America 27.6 per 100,000, which is roughly the same ratio as the frequency of high blood pressure.

Comment

It's clear that high blood pressure is commoner, treated less often, and less well treated in Europe than in the USA and Canada. What are the reasons for this quite large difference? The authors of the publication say that genetics (heredity), overweight, salt intake, lack of physical exercise, and smoking are not sufficiently different in the two regions to account for the blood pressure findings. It's possible that diet (more fruit and vegetables) and lower alcohol intake in North America may playa role.

Most likely, however, the main reason for the difference is varying thresholds for diagnosing and treating high blood pressure in each country. The standards have become much stricter in the USA and Canada in the last 20 to 30 years, so that people are diagnosed earlier and treatment started at lower blood pressure levels than in earlier times. Along with this, the stroke rates have fallen sharply in the last 30 years.

From what we know today, good control of high blood pressure is a feasible way to reduce deaths from stroke, and also, to a degree, cardiac deaths (e.g. heart attack, heart failure). To do this, however, high blood pressure must first be diagnosed, then treated adequately, and finally followed over the patient's lifetime to make sure it is kept fully under control. Sadly, this is not always achieved in North America, while in Europe the situation is even worse.