PREVENTIVE MEDECINE: HIGH BLOOD PRESSURE (HYPERTENSION)
Blood pressure goes up with age in most people in most populations that have been studied, but one study reports thirteen small populations where this does not occur and a major study in Kenya in the 1930s found that high blood pressure was hardly ever seen. A study of 1,000 post-mortems in Kenya in 1936 found that only 36 of the deaths were the result of heart disease and there were no cases of high blood pressure. Ii the early 1940s one doctor found 2 cases of high blood pressure over four years-most of those were salaried and prosperous. At this time strokes and angina were still considered to be very rare and serious hypertension was not seen in East Africa until 1953.
Today, hypertension has become a very common disease in East Africa and a review of deaths in hospitals there found that hypertension was responsible for ‘something like 40 t 60 per cent of the heart disease hospital diagnoses’. By 1978 it was the second commonest cause of death among the urbanized Bantu. Research has implicated many factor in this dramatic story but apart from the stresses of urbanization (which are difficult for quantify and are arguably not much greater than the stresses of tribal life), the amount of sail a population eats seems to be crucial. An analysis of the Kikuyu diet in 1930 found that salt was never added to food. The vast majority of the diet was unrefined starch in the form of carbohydrate (72 per cent of calorie: consumed); the rest was made up of fat (9 per cent) and protein (19 per cent). Salt intake started to rise in the 1920s and 1930s, first in urban areas. In places where diets were supervised by Europeans salt use was common.
Western man consumes 6-18 g of sodium (as common salt) daily. Primitive hunter-gatherer man consumes about 0.6 g daily. A recent study of such peoples found that their blood pressure does not rise with age.
Ethnic groups who do not add common salt “to their food have lifelong low blood pressure and no exceptions have been found to this rule. A part of this might be explained by different sensitivity to dietary salt. Genetically controlled salt sensitivity varies considerably both in animals and in man. It is now suggested that most people can tolerate a daily intake of up to about 4 g of salt but that above this level an increasing proportion of salt-sensitive subjects develop blood pressure with age. Above 6-8 g almost all salt-sensitive people will develop blood pressure with age. It is interesting that although fat people so often have hypertension in the West, obesity itself is not the cause-it is the high salt intake that so often goes with the obesity.
This knowledge has led to many trials of low-salt diets to alleviate hypertension. One major study found that reducing salt intake to 3 g daily was as effective in lowering blood pressure as drugs prescribed to another group for the same purpose. Many centers now claim to achieve normal blood pressure in their patients within a few weeks of putting them on a low-salt diet (4 g a day or less) and many people can then stop taking drugs entirely.
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Tags: General health