Tokelau Island migrant study: effect of migration on the familial aggregation of blood pressure

Abstract

This report investigates the effect of migration on the familial aggregation of BP. Subjects are from the Tokelau Island Migrant Study, a collaborative multidisdplinary study focusing on the changes in blood pressure (BP) and other variables important in cardiovascular disease that occur as a consequence of migration from an atoll homeland in the South Pacific to New Zealand. The study is unique in that the population was surveyed before migration was completed and in that both the nonmigrant population (In Tokelau) and the migrant population (in New Zealand) have been subject to a longitudinal follow-up. Differences between the migrant and nonmigrant populations were evaluated in terms of their deviation from the premigrant population. Migrants showed a considerable increase in the prevalence of hypertension, and a less marked shift in mean BP. Apart from male systolic Mood pressures (SBP), the influence of migration on the age distribution of BP was too complex to be characterized by an overall degree of elevation. For male SBP, migrants exhibited an average elevation of 10 mm Hg compared to nonmigrants. The distribution of concomitant variables was also evaluated in the three populations and found to be similar. Obesity, which (s increased in the migrants, is clearly a factor in their elevated BP, but in male migrants the increased BP appears to be due to other factors as well. Familial aggregation of BP in general showed an increase in the adult migrant population, most marked for SBP; possibly this indicates a genetic predisposition to the new environment In some adults. Alternatively, familial environments may become more heterogeneous in the new homeland. For families with juvenile offspring, the level of familial aggregation is decreased In the migrants, presumably because of rather extensive changes in patterns of growth. The path analysis method was used to separate out the effect of genetic factors and familial background; this method allows the expected correlations between BP to be expressed in terms of the underlying coefficients of determination. Results showed that in adults the effect of migration caused an apparent increase in the degree of genetic determination of BP. This indicates that a genetic susceptibility to the new environment may play an important role in the BP rise in migrants. However, for juveniles it is apparent that the disruptions in established patterns of growth, caused by migration, obscure the influence of both genetic factors and familial background. Hence, in the study of juveniles in changing environments, the study of growth and development should assume paramount importance. © 1980 American Heart Association, Inc.