By: Thomas Pickering, MD, DPhil, FRCP, Director of Integrative and Behavioral Cardiology Program
of the Cardiovascular Institute at Mount Sinai School of Medicine, New York.
In more than 95% of people who have high blood pressure, the underlying cause is listed as essential hypertension. What this means is that there is no obvious cause for the hypertension, such as a blocked renal artery. (The other 5% of people, where there is an identifiable cause, have what is called secondary hypertension.) Basically what 'essential' hypertension means is that it’s there, and we don’t know exactly why. And the 'hypertension' simply refers to the tension of pressure in the arteries; it does not, as many people might think, refer to nervous tension (although there is some recent evidence that nervous tension may contribute to its development).
The causes of essential hypertension are not well understood. However, there are several mechanisms involved, and these factors play different roles in different individuals. Probably about 50% of hypertension is genetic- you inherit some of blood pressure from your parents, just as you do your height- and the other 50% is environmental. There are almost certainly many different genes involved, and scientists are busily searching to identify them.
There is a lot of controversy as to what are the important environmental factors. One of the strongest bits of evidence showing that the environment you live in affects your blood pressure comes from 'acculturation' studies, in which people who live in traditional non-westernized societies are studied before and after they move to a modern city. Many of these studies have been done in Africa. What they show is that adopting a western lifestyle is associated with a marked increase of blood pressure, which may be caused by the change in diet (salt intake typically goes up), or by stress, or probably both This relates to why hypertension is so much commoner in blacks in the US than in whites: in rural Africa hypertension is relatively rare, suggesting that the high prevalence in the US is not because of a genetic tendency.
Of the environmental factors that cause high blood pressure the two leading candidates are thus stress and diet. One reason why we can't be more sure about their exact roles is that both are complex and hard to measure. Stress, like beauty, is in the eye of the beholder, and what is stressful to me is not necessarily so stressful to you. And trying to score your level of stress so that we can compare it with mine is obviously very arbitrary. Diet is in principal easier to measure, but people vary what they eat from day to day, and there are almost certainly many ingredients other than salt and calories, which affect the blood pressure, which we are only just beginning to understand.
