Hypertension 1996 : One Medicine, Two Cultures

Epidemiologic aspects of hypertension in the world

Dr. Fernando S. Antezana
Assistant Director-General
World Health Organization

Cardiovascular diseases (CVD), most of which are due to atherosclerosis (mainly heart attack and stroke) and often related to arterial hypertension, are responsible for nearly 20% of all deaths world-wide (nearly 10 million). They are the principal cause of death in all developed countries accounting for 50% of all deaths and are also emerging as a prominent public health problem in developing countries, ranking third with nearly 16% of all deaths. They have already become the first cause of death in such countries as Argentina, Chile, Cuba, Mauritius, Singapore, Sri Lanka, Trinidad and Tobago and Uruguay. Many developing countries are now in a phase of epidemiological transition and face the double burden of communicable and non-communicable diseases, with the severe repercussions this has on their very weak economies.
Arterial Hypertension (AH) is the most common cardiovascular disease and is a major public health problem in both developed and developing countries. It produces a marked effect on patients, relatives and society, either because of hypertension per se or through its complications (stroke, heart attack, ischaemic heart disease, renal dysfunction and heart failure) which can produce premature death or permanent disability. The risk of developing a cardiovascular complication is higher when the individual combines hypertension with other risk factors such as hypercholesterolemia/dislipidemia or smoking.
Epidemiological studies show that there are significant geographical differences in the occurrence of arterial hypertension and its complications both between and within countries; this is considered to be influenced by the interaction of nutritional and environmental factors with the subject's genetic predisposition/susceptibility to develop AH.
It is known that more than 95 % of hypertensive patients in the community are of essential or idiopathic/unknown aetiology, and only a small percentage have an identifiable cause (secondary hypertension).
Epidemiological evidence also shows that there are several factors which play an important role in the development, evolution and prognosis of arterial hypertension, some of them non-modifiable, such as age, sex, ethnicity and heredity, and others modifiable, such as body weight, salt intake, alcohol intake, use of hormonal contraceptives and drugs retaining sodium, sedentary life and psychosocial factors.

Non-modifiable

Age

Mean systolic and diastolic blood pressure and prevalence of AH increase with age throughout childhood, adolescence and adulthood in most populations of developed and developing countries. However, in some isolated populations, this age-related rise of blood pressure (BP) is not evident.

Sex/gender

Men tend to display higher blood pressure than women, more evident in youth and middle-age. Later in life (over 50 years old), the difference narrows and the pattern may be reversed.

Heredity

Although the precise mode of heredity/inheritance has not yet been demonstrated, a high occurrence of hypertension is observed among subjects with a family history of hypertension and it is higher and more severe when both parents are concerned.

Ethnicity/race

Studies have also revealed higher blood pressure levels in the black community than in other ethnic groups, mainly in black Afro-Americans with early onset, severity and appearance of complications.

Modifiable

Body weight

Evidence from cross-sectional and longitudinal studies show a direct, strong and consistent relationship between weight and blood pressure. This is valid in primitive and advanced cultures, as well as in childhood and adulthood. Individuals who gain weight have a twofold to sixfold greater risk of developing hypertension. Moreover, weight reduction has been accompanied by a fall in blood pressure and in antihypertensive drug consumption.

Sodium chloride intake

Experimental and observational studies have shown that the intake of sodium chloride, in excess of the physiological requirements (5-7 gr per day), is associated with high blood pressure; communities whose daily intake of sodium is low (less than 3-4 gr.) have low average blood pressure. A lower intake of sodium over a lifetime would result in a smaller rise in blood pressure and a significant reduction in mortality from coronary heart disease and stroke.

Potassium

There is an inverse relationship between blood pressure and dietary intake of potassium.

Alcohol intake

A consistent association between alcohol intake and high blood pressure has been observed. Both acute and chronic effects have been noted and this association is more evident in daily drinkers.

Physical activity

There is a negative relationship between aerobic physical activities and blood pressure; sedentary and unfit normotensive individuals have a 20-50 % greater risk of developing hypertension during follow-up than their more active and fit peers. Regular aerobic physical activity has been demonstrated to be beneficial for both prevention and treatment of hypertension.

Psychosocial factors

There is some evidence that adverse psychosocial environments might increase blood pressure. However, they are insufficient to allow definite conclusions of causality.

Socio-economic status

In developed countries with affluent economies, higher levels of blood pressure and higher prevalence of hypertension in lower socio-economic groups have been noted; this inverse relation has been also noted with levels of education, income and occupation. In societies that are in the transitional stage of economic and epidemiological change, higher levels of blood pressure and a higher prevalence of hypertension have been noted in upper socio-economic groups.

Hormonal contraceptives

Prospective controlled studies have shown that estrogen-progestogen contraceptives cause a distinct increase in blood pressure in virtually all women. Almost invariably blood pressure falls when the oral contraceptive is withdrawn. Micronutrients such as calcium, magnesium, cadmium and zinc, and macronutrients such as fat, fatty acids, carbohydrate, fibre and protein have been investigated in several populations. However, there is as yet no evidence of a causal relationship with high blood pressure.
The World Health Organization has been concerned with AH since the 1950s. It has directed its efforts towards diagnostic criteria, standard methods and guidelines for measurement, epidemiological aspects, history, management, prevention and control of AH (the most recent report is the 1996 WHO Technical Report Series No 862 "Hypertension Control").

Epidemiological pattern

In the last 30 years there has been a change in cardiovascular mortality trends. A decline in arterial hypertension mortality and its complications, mainly coronary heart disease and stroke, has been observed in several developed countries of North America, Western Europe and the Western Pacific. However prevalence and incidence of hypertension have only slightly changed though a marked increase in these countries in the frequency of hypertensive patients aware of the disease and undergoing treatment for hypertension and blood pressure controls. However, the contrary has been noted in other countries, mainly in Central and Eastern Europe and several developing countries.
Studies in developed countries reveal a large variation in the prevalence of arterial hypertension and the frequency of hypertensive patients undergoing treatment and blood pressure controls, with prevalence of hypertension higher than 30.0 % in the Czech Republic, Germany and Malta, and lower than 15.0 % in Spain and Belgium. The percentage of hypertensives undergoing treatment and blood pressure controls was high in Belgium and Spain, and low in Glasgow, UK, Malta and Kaunas, Lithuania (Table I).

Few accurate data are available on CVD and AH morbidity and mortality from most developing countries. However, from available data we can remark that hypertension is the most frequent cardiovascular disease and a major health problem in the adult population of most developing countries. The prevalence of hypertension also has a marked variation among and within developing countries. It is lower than in developed countries, with high prevalence in Barbados, Brazil, Chile and Cuba, and lower prevalence in Asian and African countries, such as China, India, Nepal, Senegal, Tanzania and Zaire; with a lower percentage in rural areas. The few data from developing countries show, in general, a very low percentage of hypertensive patients undergoing treatment and blood pressure controls (Table II).

Multinational studies on community control of arterial hypertension in several centres, including developed and developing countries have shown a marked decrease in the mean systolic and diastolic blood pressure. A large increases in percentages of hypertensives aware of the disease, and undergoing treatment and blood pressure controls was observed after five years of intervention and a decline in total mortality and mortality due to stroke and ischaemic heart disease was noted. Females are treated and controlled more frequently than males. The same benefit, although to lesser degree, was seen in the reference areas.

Principle for prevention and control

The prevention of complications resulting from high blood pressure in any population requires reducing the risk of developing high blood pressure in the population as a whole (population approach) and identifying individuals with hypertension, who are at increased risk of developing complications, for further treatment and control through pharmacological and non-pharmacological therapy-weight reduction, alcohol intake reduction, moderation of dietary sodium, increasing physical activity, traditional medicine (individual approach). Combining the individual approach with the population approach provides a comprehensive strategy for the prevention and control of hypertension and its complications at the community level and lies within the context of the integration of the prevention and control of cardiovascular diseases/non-communicable diseases into the primary health care system of a country.
In closing this summary review of epidemiological aspects of hypertension in the world, I wish to underline three points:

  1. The situation of epidemiological transition in developing countries, with its double burden of communicable and non-communicable diseases. Amongst the latter, AH ranks the highest.
  2. The close linkages between AH and lifestyles, environment, behaviour, etc., in the modern society (modifiable factors).
  3. The management of AH today requires the contribution of pharmacological and non-pharmacological approaches.

Taking into account the various determinants of hypertension, including psychosocial factors, the so-called "two cultures" approach can be very useful in the management of AH. This approach provides the opportunity for complementary therapy in today's world where, for every health problem, one tends to look for technological solutions without perhaps considering the application of very effective non-pharmacological techniques.

 

 

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Edited by Aldo Campana,