Effect of migration on blood pressure: the Yi People Study

The Yi People Study was conducted in Puge County, Sichuan Province, People's Republic of China. Four population groups were surveyed for risk factors for cardiovascular disease. Included were two groups of Yi farmers living either in a high mountainous area in extremely remote villages at or above 2,750 meters elevation, or in a mountainside area at about 1,800 meters elevation. A third study group consisted of Yi farmers who migrated to the county seat during the 1950s. Local residents of the county seat, the Han people, constituted the fourth group. Blood pressure rises very little with age after puberty in Yi farmers, but there was a trend of increasing blood pressure with age in Yi migrants and Han. Mean body mass index (kg/m2) and heart rate were higher in Yi migrants than in Yi farmers. For men, both systolic and diastolic blood pressure were greater among Yi migrants than among Yi farmers. These differences persisted after adjusting for age and body mass index. Among women, after adjusting for age, BMI, and altitude, only diastolic blood pressure was lower among Yi farmers than Yi migrants. Yi migrants and Han had similar blood pressures. In 1986, a sample of men participated in more detailed studies of diet, serum, and urine. The proportion of energy from fat ranged from less than 10% among high-mountain Yi farmers to almost 40% among Yi migrants and Han. Compared with Yi farmers, Yi migrants consumed more sodium and less potassium, calcium, and magnesium, had lower serum potassium, and a greater sodium/potassium ratio. Urinary excretion of sodium, calcium, and the sodium/potassium ratio were all greater in Yi migrants than in Yi farmers, while the reverse was seen for potassium. These data suggest that changes in life-style, including dietary changes, contribute importantly to the higher blood pressure among Yi migrants.