Immigrant assimilation and BMI and waist size: a longitudinal examination among Hispanic and Chinese participants in the multi-ethnic study of atherosclerosis

Abstract

Objective: US birth and longer length of US residence among the foreign-born have been linked to higher anthropometric measures. However, previous studies have been cross sectional and few have examined heterogeneity by ethnic group. Cross-sectional findings that show immigrant weight converging to US-born levels with longer time in the United States imply that immigrants' weight is increasing at a faster rate relative to US-born individuals. Prospective studies are necessary to confirm this pattern.

Design and methods: Using longitudinal data from 1,486 Hispanic and 802 Chinese adults aged 45-84 years in the Multi-ethnic Study of Atherosclerosis, we examined whether foreign-born participants experienced greater increases in BMI and waist circumference (WC) than the US-born over a median follow-up of 5 years. We also investigated heterogeneity in these associations by Hispanic subgroup.

Results: Among Hispanics and Chinese, the foreign-born had a lower adjusted mean BMI and WC at baseline than the US-born, but there were no significant differences in BMI or WC change over time. There was heterogeneity by Hispanic subgroup: despite small baseline nativity differences in WC, foreign-born Mexican Hispanics had a greater annual mean increase in WC over time compared to US-born Mexican Hispanics (mean difference in annual change = 0.28 cm, P = 0.03). There were no nativity differences in the rate of WC increase over time among non-Mexican Hispanics. Foreign-born Mexican Hispanics also experienced a faster rate of WC increase compared to foreign-born non-Mexican Hispanics (mean difference in annual change = 0.24 cm, P = 0.01).

Conclusions: Longer time in the United States, examined prospectively, may only be linked to adverse anthropometric changes in some immigrant groups.

Figure 1

Adjusted mean waist circumference trajectories over time by baseline length of U.S. residence among the foreign-born and the U.S.-born. A) Mexican Hispanics, B) Non-Mexican Hispanics, C) Chinese. WC=waist circumference; Yrs=years. All models adjusted for age, sex, site, education, income, baseline length of U.S. residence, age*time, education*time, income*time, baseline length of U.S. residence*time, and health behaviors (physical activity, smoking, alcohol, and diet). Estimates shown were calculated to correspond to the mean age of the entire sample (age=63) and to those with less than high school education and in the lowest income quartile. Foreign-born with missing data on baseline length of U.S. residence included in all models but not plotted in figures.

Figure 1

Adjusted mean waist circumference trajectories over time by baseline length of U.S. residence among the foreign-born and the U.S.-born. A) Mexican Hispanics, B) Non-Mexican Hispanics, C) Chinese. WC=waist circumference; Yrs=years. All models adjusted for age, sex, site, education, income, baseline length of U.S. residence, age*time, education*time, income*time, baseline length of U.S. residence*time, and health behaviors (physical activity, smoking, alcohol, and diet). Estimates shown were calculated to correspond to the mean age of the entire sample (age=63) and to those with less than high school education and in the lowest income quartile. Foreign-born with missing data on baseline length of U.S. residence included in all models but not plotted in figures.

Figure 1

Adjusted mean waist circumference trajectories over time by baseline length of U.S. residence among the foreign-born and the U.S.-born. A) Mexican Hispanics, B) Non-Mexican Hispanics, C) Chinese. WC=waist circumference; Yrs=years. All models adjusted for age, sex, site, education, income, baseline length of U.S. residence, age*time, education*time, income*time, baseline length of U.S. residence*time, and health behaviors (physical activity, smoking, alcohol, and diet). Estimates shown were calculated to correspond to the mean age of the entire sample (age=63) and to those with less than high school education and in the lowest income quartile. Foreign-born with missing data on baseline length of U.S. residence included in all models but not plotted in figures.