| There is no evidence that average blood pressure | | | | difference in smoking habits, but some of the |
| in the whole of the general population has risen | | | | changes to the pattern may now be caused by |
| over the seventy or so years over which | | | | these variations in average blood pressure and |
| measurements are available. There is some | | | | perhaps by access to accurate diagnosis and |
| indirect evidence that it may be lowered and may | | | | effective treatment. |
| still be falling quite independently of medical | | | | It should be noted that blood pressure also varies |
| treatment. Whatever the definition of high blood | | | | between races and different sorts of societies, |
| pressure used, the proportion of people with high | | | | but why it does is not an easy question to |
| blood pressure is directly related to average | | | | answer. A number of different factors have been |
| pressure throughout the population. | | | | considered. High blood pressure is a serious |
| Standardized and accurate measurements of | | | | problem throughout black Africa and black people |
| blood pressure for large representative | | | | in North America have much higher blood |
| populations have only been available since the | | | | pressure and stroke problems than Caucasians. |
| 1950s in the United Kingdom, Scandinavia and the | | | | However, the differences between black and |
| United States and more recently for other | | | | white North Americans disappear if differences in |
| countries. There is some evidence from countries | | | | income are taken into consideration. In the 1960s |
| whose general diet has shifted from very high to | | | | and 1970s, comparisons between British citizens |
| much lower salt intakes - specifically Japan, | | | | of Afro-Caribbean and European descent showed |
| Belgium and Portugal - that average blood | | | | no differences, but more recent studies have |
| pressure in the general population has fallen, | | | | begun to show the same differences an in the |
| probably for this reason. These reductions in salt | | | | USA. |
| intake reflect shifts in methods of food | | | | These differences are evident in the social aspect, |
| preservation from the traditional methods of | | | | rather than racial and social differences in average |
| salting, pickling and smoking to the modern | | | | blood pressure seem to depend mainly on income |
| methods of refrigeration and rapid transport of | | | | differences. When North American incomes were |
| fresh food. As these changes have occurred in | | | | much more polarized than British incomes, social |
| most economically developed countries, average | | | | differences in the average blood pressure were |
| blood pressure has probably fallen everywhere, | | | | much higher in the USA than in the UK, but there |
| compared with average levels in the 19th century. | | | | is evidence that as these societies converge, |
| Research in the USA has always shown higher | | | | social differences in average blood pressure are |
| average blood pressures in poorer people. | | | | becoming similar in the two countries. |
| Although research in this country in the 1950s and | | | | Recent changes in the national health care system |
| 1960s failed to show any systematic difference | | | | contract for general practitioners should have led |
| between social groups, this seemed to have | | | | to most people with high blood pressure being |
| changed by the 1980s, with higher average blood | | | | identified, although it is much more doubtful |
| pressure in poorer populations throughout the UK. | | | | whether most of these are followed up with |
| These differences in average blood pressures are | | | | effective treatment. If all general practice teams |
| not too large, but differences in other risk factors | | | | developed cardiovascular follow-up clinics for high |
| for heart disease show the same trend. Although | | | | blood pressure on the same lines as the best |
| there is some evidence that coronary heart | | | | have already done and all their patients were |
| disease became common after World War I and | | | | treated to the level of quality attained in large |
| that it started among rich people, ever since the | | | | clinical trials, an additional 15% of fatal strokes |
| 1950s it has more and more become a disease | | | | would be prevented and probably 5% of coronary |
| for poorer people. This is partly because of the | | | | heart disease. |