Consistent with findings from prior studies, place of birth and duration of residence in the U.S. predict BMI among residents of New York City overall, but with some differences in associations by race/ethnicity [9, 11, 14, 15, 33]. Associations between place of birth and BMI are strongest for Blacks from the Caribbean, intermediate for Caucasians and Hispanics, and weakest for Asians. The borderline statistical significance for Asians and Blacks from the Caribbean probably reflects the small numbers of U.S.-born subjects included in analyses for these two groups. In the overall study population, immigrants who had lived in the U.S. for the shortest duration had the lowest mean BMI score, and there was a significant trend across duration of residence categories. Across racial/ethnic groups, the trend of higher mean BMI score with increased duration of residence was strongest and most consistent among Hispanics. The trend was less consistent among Black – Caribbeans and Caucasians.
Similar to the finding for place of birth, the association between duration of residence in the U.S. and BMI was weakest among Asians. But the modest associations of borderline statistical significance among Asian may, nevertheless, be important. Research suggests that Asians have a higher percentage of body fat for a given BMI compared to Caucasians, and that the threshold for developing obesity and nutrition related non-communicable diseases (NR-NCD) in Asians occurs at a lower BMI level than for other populations . Thus, even the modest increase in BMI among Asians associated with place of birth and length of residence in the U.S. seen in our sample may be of public health significance.
Findings such as ours have been generally interpreted to suggest that the U.S. has an obesogenic environment, that is, U.S. norms favor a positive energy balance and weight gain as compared to the home countries of the immigrants [2, 9, 11, 15]. Being U.S.-born is associated with a significantly higher BMI, and greater length of residence in the U.S. is associated with higher BMI, because, it is thought, both variables capture aspects of an individual's level of acculturation to that obesogenic environment [9, 11]. In order to better understand the factors that comprise this acculturative process, we included analyses of neighborhood measures of immigrant composition. We examined whether the proportion of foreign-born residents and proportion of linguistically isolated residents living in an individual's home neighborhood was associated with BMI over and beyond the individual's place of birth and length of residence in the U.S. Prior literature on linguistic isolation has predominantly investigated the language usage of the study subject and their family, not the extent to which residents of the neighborhood the subject lives in utilize English .
If, as the literature indicates, increased acculturation to an obesogenic environment has a detrimental health effect on immigrants, then neighborhood/community factors that retard that process of acculturation should be health promoting. It has been suggested, for instance, that disease patterns among immigrants who retain food consumption patterns of their country of origin remain more consistent with those of the home country than that of the U.S. [35, 36]. If, as Gordon-Larsen and colleagues theorize, that "Where immigrants settle has substantial implications for dietary and activity patterns, given availability of markets that supply foreign versus American goods and services ," then residence in neighborhoods with high concentrations of immigrants should reduce the influence of U.S. dietary and physical activity norms that are thought to comprise the obesogenic environment of the U.S. . Although their study of adolescent body size is not completely congruent with ours, Gordon-Larsen and colleagues analyzed proportion foreign-born and proportion Hispanic as measures of neighborhood level acculturation status but did not find these variables to be associated with overweight . They also evaluated neighborhood linguistic isolation but did not include the variable in the final regression models . Despite these measures not being significantly predictive of overweight status themselves, the inclusion of the acculturation variables in the model did reduce the effect of generation of immigration in Puerto Ricans and Cubans . Another study utilized Census tract level proportion Hispanic as a predictor of adult BMI among Mexican-Americans, but after control for measures of neighborhood level socio-economic status this measure of neighborhood immigrant composition was not associated with BMI . Among Caucasians, increasing neighborhood proportion foreign-born was associated with lower BMI with borderline statistical significance, suggesting that living in an immigrant neighborhood is protective for this group. Of the neighborhood context variables the only statistically significant finding was for neighborhood linguistic isolation being inversely associated with BMI among Hispanics. Predictably, for Caucasians and Black – Caribbeans, the two groups for whom linguistic isolation would not be thought to provide a protective effect, linguistic isolation was not associated with BMI. Additionally for Hispanics, in neighborhoods with high levels of linguistic isolation, place of birth was not associated with BMI, where as in neighborhoods with lower levels of linguistic isolation, there was a strong association between place of birth and BMI. Among Hispanics, those who were born in the U.S. and living in neighborhoods with low levels of linguistic isolation had the highest BMI scores. Similar to the two prior neighborhood studies investigating proportion Hispanic as a predictor, no association with proportion Hispanic was observed in the data. We believe that this is the first report to investigate whether there is statistical interaction between an individual's nativity and measures of neighborhood immigrant composition.
These findings are consistent with recent literature regarding acculturation and the "Hispanic Paradox", the observation of better health among first generation Hispanic immigrants [37, 38]. The relative better health of the recent Hispanic immigrants is thought to be due to the group level maintenance of beneficial health behaviors practiced in the home country. As individuals acculturate to U.S. behavioral norms, the maintenance of home country health practices and their health status decline [37, 38]. Communities with a high degree of linguistic isolation are more likely to be resistant to the adoption of U.S. norms and to maintain home country norms regarding body size. Consistent with this idea, our findings indicate that neighborhood level linguistic isolation is protective against increased body size, and particularly for U.S. born Hispanics, residence in less acculturated areas is beneficial. An interesting question our study raises, however, is why a similar neighborhood effect is not apparent among other immigrant groups. Among Hispanics, neighborhood effects occur because theoretically linguistic isolation signifies the presence of neighborhood characteristics that protect against health compromising behaviors. Why is this not true for other groups? For our sample, at least, the paradox of the neighborhood effect is why it is a Hispanic, rather than an immigrant, effect.
Overall, and among Hispanics, there were significant and strong positive associations between years of residence in the U.S. and BMI, but among Asians, the association between duration and BMI was very modest and of borderline statistical significance. This finding may be interpreted in several ways. Asians may, in fact, differ from other immigrant groups and not experience major weight gain despite lengthy residence in the U.S. However, past analyses of the 1992–1995 National Health Interview Study (NHIS) data on Asians showed that the odds of being overweight and obese increased with length of residence in the U.S. . More recent analyses of the 2000 NHIS found results similar to those presented here: length of residence in the U.S. was associated with significant weight gain in Whites and Latinos, while among Asians weight gain with duration of residence was more modest and of borderline statistical significance . Previous studies on BMI and immigration across ethnic groups have suggested that differences in weight gain across ethnic groups can be ascribed to differences in acculturation rates .
Conversely, the lack of association between duration of residence and BMI may represent cohort effects expressed in cross sectional data analyses. Like most prior work on length of residence and BMI, the analyses presented here are cross-sectional in nature and interpretation depends on the assumption that recent and earlier waves of immigrants had a similar BMI when they arrived in the U.S. However, if this assumption does not hold, home country trends could mask increases in BMI experienced by earlier waves of immigrants. For example, a recent nationally representative study in China showed a 50% increase in the prevalence of overweight and obesity from 1992 to 2002 . Many Asians emigrate today from nations whose nutritional and physical activity profiles have changed dramatically in recent years, and it is possible that recent immigrants are arriving in the U.S. with higher BMI than did earlier cohorts. If this is indeed the case, even if the BMI of earlier cohorts has increased during their residence in the U.S., the gain would not be apparent in cross sectional analyses of duration of residence. Likewise, other cohort effects may obscure temporal trends in BMI when data are analyzed in a cross-sectional fashion as presented here. For instance, within the racial and ethnic classifications presented here, duration of residence may be associated with waves of immigration from different countries of origin that have different dietary and physical activity norms and in turn different BMI profiles. However, even with the large sample size available here, further analyses stratified by country of origin were not possible.
Particularly in an international city such as New York City, it maybe useful to think of the global epidemic of overweight and obesity as a cause of local trends in body size. Overweight and obesity has now become a global problem with a greater increase in obesity in lower- and middle-income developing countries than in high-income countries, and a world wide shift in the burden of obesity down the socio-economic scale [40–42]. The dominant models of acculturation which assumes acculturation as a post-migration process need to be reconsidered . Recent immigrants come from home cultures which have already been profoundly affected by the influences of U.S. media and commerce, and have undergone significant economic and social changes which are reflected in shifts in diet and physical activity patterns. What is currently interpreted in the literature as post-migration effects of acculturation may in fact be a reflection of changes in norms that are taking place elsewhere.
Additionally, immigrants' post-migration contact with their countries of origin, and the shifts in their cultures of origin, must be considered. What researchers theorize as a linear process of acculturation to the U.S. might, in actuality, represent changes in immigrants' home culture transmitted to immigrants in the U.S. Foreign language media penetration in the New York City market is considerable. For example, during the 2005 July sweeps period, Univision, the Spanish language station with programs largely originating from South and Central America, drew more viewers than all other stations among 18–49 year olds, Hispanic or otherwise . Whether garnered through media or through travels back to the country of origin, immigrants' post-migration acculturation may be affected by cultural shifts in that of the country of origin. That acculturation might be mediated – made more or less attractive or at least filtered and interpreted in various ways – through the home country's globalization rather than through direct experience, must be considered.
A number of methodological issues should be considered when interpreting these results. Socio-economic status was controlled for using information on educational status. Educational systems, however, vary across countries and thus educational attainment may not adequately control for confounding by socio-economic status, although income no longer predicts BMI once education is included in the regression model . We also note that further control for neighborhood level proportion poverty did not alter the associations between BMI and place of birth or duration of residence. Additionally, individuals born in Puerto Rico, although U.S. citizens, were considered to be foreign-born in these analyses. This approach is consistent with analyses conducted by the Pew Hispanic Center, which notes that island born Puerto Ricans are born into a culture dominated by Spanish and their views and beliefs are much closer to foreign-born Hispanics than U.S. born Hispanics . However as we note above, with globalization and the rise of Spanish language media reducing cultural distances, it is debatable as how best to classify island-born Puerto Ricans for analyses such as these. Unlike the Hispanic Health and Nutrition Examination Survey and other studies that sampled on, or over sampled for, country or territory of origin, we did not have sufficient numbers of individuals to finely categorize Hispanics into ethnic sub-groups. There is some evidence that the association between BMI and measures of acculturation varies across ethnic groups within the larger Hispanic designation [2, 12]. While we were not able to perform stratified analyses as conducted elsewhere, our analyses did control for Puerto Rican, Dominican or other country of origin. Lastly as noted above, the study is limited by its cross-sectional design and inability to make prospective causal inferences.
In conclusion, a necessary component to understanding immigrant health is information on patterns of nutrition, physical activity, and body weight beliefs/values and behavior/practices in the immigrants' countries of origin. This information would allow for a comparative context against which immigrants' current practices and beliefs and perceptions of cultural beliefs and practices of their countries of origin can be understood. The compilation of relevant socio-demographic and epidemiological information from the immigrants' countries of origin would allow useful comparisons necessary to understanding immigrants' decision making processes and acculturative patterns in the U.S.