The British-Norwegian migrant study--analysis of parameters of mortality differentials associated with angina.

The prevalence of selected cardiorespiratory symptoms was ascertained by a common mail questionnaire for 73,884 men and women in the United States, Great Britain and Norway. The study groups were identified in the early 1960's and included 30,033 British and Norwegian migrants to the United States and 43,851 non-migrants who resided in Great Britain and Norway. The main study objectives were to contrast the morbidity and mortality experience of the migrant and non-migrant groups in the light of known national differences in mortality from cardiorespiratory diseases in the early 1960's. At that time, the U.S. had the highest death rates from coronary heart disease while Great Britain had the highest rates for lung cancer and for chronic non-specific lung disease. Norway had the lowest rates for all three rubrics. The prevalence of "angina" and other symptoms was ascertained for each of the study groups. Contrary to expectation, angina was reported much more frequently by persons remaining in Britain and Norway than by migrants to the United States. Mortality rates during the five years and responding to the symptoms questionnaire were determined and mortality patterns were evaluated according to the presence or absence of angina. Angina was found to be a strong predictor of cardiovascular mortality. In the absence of angina, it was observed that migrants had similar mortality rates to non-migrants regardless of country of origin. However, the British had higher mortality rates from cardiovascular and from non-cardiovascular causes than the Norwegians. The primary determinant of angina prevalence was found to be migration status. It is believed that this differential was determined primarily by selection of those who migrate, with the migrants to the U.S. being a healthier group than their counterparts remaining in the native country.