Convergence of body mass index of immigrants to the Canadian-born population: evidence from the National Population Health Survey (1994-2006)

Recent immigrants typically have better physical health than the native born population. However, this 'healthy immigrant effect' tends to gradually wane over time, with increasing length of residence in the host country. To assess whether the body mass index (BMI) of different immigrant groups converged to the Canadian population's levels, we estimated 12-year trajectories of changes in BMI (accounting for socio-demographic changes). Using data from seven longitudinal waves of the National Population Health Survey (1994 through 2006), we compared the changes in BMI (kg/m(2)) among three groups: white immigrants, non-white immigrants and Canadian born, aged 18-54 at baseline. We applied linear random effects models to evaluate these BMI separately in 2,504 males and 2,960 females. BMI increased in Canadian born, white immigrants, and non-white immigrants over the 12-year period. However, non-white immigrants (males and females) had a lower mean BMI than Canadian born individuals during this period [Males: -2.27, 95% Confidence interval (CI) -3.02 to -1.53; Females: -1.84, 95% CI -2.79 to -0.90]. In contrast, the mean BMI in white male immigrants and Canadian born individuals were similar (-0.32, 95% CI -0.91 to 0.27). Even after adjusting for time since immigration, non-white immigrants had lower BMI than white immigrants. White male immigrants were the only sub-group to converge to the BMI of the Canadian born population. These results indicate that the loss of 'healthy immigrant effect' with regard to convergence of BMI to Canadian levels may not be experienced equally by all immigrants in Canada.