Longitudinal study of body mass index in Asian men who immigrate to the US

Background and Objectives: Cross-sectional studies indicate that adaptation to Western norms, especially at a younger age, might explain the higher average body mass index (BMI) among Asians living in the United States (US) compared to Asians living in Asia. However, migrants differ from non-migrants in sociocultural factors that are difficult to measure and, thus, longitudinal studies on the same individuals prior to and after immigration are needed. The objective of this study was to determine differences in changes in BMI across age by residence (US or Asia) and age at immigration using longitudinal data on BMI prior to and after immigration. Methods and Study Design: The California Men's Health Study includes 1,549 foreign-born Asian men who were aged 44-71 at baseline in 2002-03. BMI at ages 30, 40, 50 and 60 was calculated using self-reported weight history and current height. Residence at each age decade and age at immigration were determined. Data were analyzed using generalized estimating equations. Results: Ten-year BMI increases were smaller among Asians who lived in Asia prior to migrating to the US compared to those who already lived in the US. This effect was most evident between ages 30-40 when Asians in Asia had a 0.69 kg/m(2) (95% CI: -1.08, -0.30) smaller increase in BMI. Immigrants who moved to the US before age 40 experienced greater increases in BMI than immigrants who moved to the US at an older age. Conclusion: This study is the first to support the hypothesis that living in the US and younger age at immigration results in larger BMI increases in Asian men.