Elsevier

Nutrition

Volume 23, Issue 9, September 2007, Pages 696-708
Nutrition

Review
Migration and its impact on adiposity and type 2 diabetes

https://doi.org/10.1016/j.nut.2007.06.008Get rights and content

Abstract

In this review, we discuss the impact of migration on the incidence and prevalence of obesity and type 2 diabetes mellitus (T2DM) in different ethnic groups and populations. We also analyze the determinants of such phenomena in view of the global increase in the migration and escalating prevalence of obesity and T2DM. The risk escalation of the obesity and T2DM followed a gradient, as migrants (Blacks, Hispanics, Chinese, South Asians, etc.) became more affluent and urbanized, indicating an important role of environmental factors. A stepwise increase in the prevalence of obesity in Blacks along the path of migration (5% in Nigeria, 23% in Jamaica, and 39% in the United States) is a classic example. Furthermore, South Asian migrants, who are particularly predisposed to develop insulin resistance and T2DM, showed nearly four times prevalence rates of T2DM than rural sedentee populations. Similar observations were also reported in intracountry migrants and resettled indigenous populations. The determinants were found to include nutrition transition, physical inactivity, gene-environment interaction, stress, and other factors such as ethnic susceptibility. However, certain contradictory trends were also seen in some migrant communities and have been explained by various phenomena such as healthy migrant effect, “salmon bias”, and adherence to traditional diets.

A review of the evidence suggests a critical role of environmental factors in conferring an increased risk of obesity and T2DM. The important contributory factors to this phenomenon were urbanization, mechanization, and changes in nutrition and lifestyle behaviors, but the role of stress and as yet unknown factors remain to be determined.

Introduction

Migration of populations is an ancient phenomenon, happening from the time of our ancestors in Africa. A variety of reasons may contribute to this phenomenon. Migration can occur due to “push factors,” i.e., poverty, war, etc., in the native country, or “pull factors,” i.e., toward better educational, financial, or career opportunities in the country of migration. One of the largest migrations occurred to the United States from Europe in the 18th and 19th centuries. More recently, migration has become much more frequent with increasing global opportunities in business and technology and frequent international travel. It provides a unique opportunity to study the influence of various environmental factors on secular trends and risk factors of various predominantly environmentally influenced diseases such as obesity and type 2 diabetes mellitus (T2DM). The purpose of this paper is to review the effect of migration on the incidence and prevalence of T2DM and obesity in different ethnic groups and populations. We also discuss the various determinants of such phenomena in different migrant ethnic groups followed by a discussion on migration-linked determinants of adiposity, T2DM, and cardiovascular disease (CVD).

The search strategy for literature review was as follows. An electronic literature search was carried out by using the terms “immigrants or migrants and obesity and diabetes or type 2 diabetes mellitus” in the databases of 1) PubMed (National Library of Medicine, Bethesda, MD, USA) from 1966 to March 2007 and 2) Current Contents (Institute for Scientific Information, Thomson Scientific, Philadelphia, PA, USA). The studies were selected based on their relevance and importance in the context of the topic. Those appearing in high-impact and internationally acknowledged journals were given preference. A manual search of the relevant articles from the published references was also conducted. Databases, non-indexed publications, and web sites of reputed medical research and public health institutions of the United States, United Kingdom, Canada, India, and other countries were also researched using general web-based search engines.

Section snippets

Definition and patterns

The term “migrant populations” usually refers to migration from a native country to another country; however, in a broader perspective, it may be applied to the migration from one habitat to another within a country (e.g., rural-to-urban migration). In the early 19th century, migrants represented mainly people who were laborers, farm workers, refugees, etc., but lately, academically accomplished, and economically well-off migrants have begun to settle in developed countries due to industrial

Migration and diseases

It has been long observed that the processes of urbanization or westernization associated with migration lead to the availability and abundance of calorie-dense/low-fiber foods and the adoption of sedentary lifestyles. This has consequently led to increased risks of morbidity and mortality from chronic diet and lifestyle-related diseases. The pattern has been seen in cross-country and intracountry migration in developed and developing countries.

Several studies during the past four decades have

Obesity and T2DM in different ethnic migrant populations

Since Taylor and Zimmet [10] reviewed the impact of migrant studies in the epidemiology of T2DM two decades ago, no review of this subject has been published. In view of the global increase in migration and the escalating prevalence of T2DM and the variable increase in various regions of the world (well documented by the World Health Organization [WHO] and the International Diabetes Federation (Fig. 1[11]), the issue assumes even greater importance in terms of studying the recent trends. In the

Intracountry migration and resettlements

The migration within a country may occur from a rural to an urban habitat or from the traditional habitat to government-selected reservations or missions. The following descriptions of such migrant populations provide a reflection of how nutritional and lifestyle transitions have affected the health status of people living within the same country.

The Aboriginal and Torres Strait Islanders, traditionally being hunters and gatherers, were resettled in government-made reservations. However, they

Pitfalls of the migrant studies

Studies relating to migrant populations are difficult to perform because of numerous and continuously changing variables. First, the migrant population may not typically represent the general characteristics of the sedentee population, and they may be healthier or less healthy than sedentees due to various factors outlined previously. Second, the increasing global reach of the Western food industry, spurred on by the barrage of advertisements in audiovisual media, is radically influencing the

Determinants of obesity and T2DM in migrant populations

Although the following section lists individual factors, usually there is a complex interplay of several factors, which may determine the adverse metabolic changes and the prevalence of T2DM on migration (Fig. 4).

Summary

Environmental factors seem to play a critical role in conferring an increased risk of obesity, insulin resistance, T2DM, and CVD. Although the remnant genetic effect has been dominant in certain situations, influences of environmental and acquired factors on cardiovascular and metabolic risks often override genetic influences. Most environmental factors are due to technologic and social progress: urbanization, mechanization, changes in nutrition, physical activity, smoking, and alcohol intake.

Acknowledgments

The authors thank Dr. Lokesh Khurana for reviewing and editing the manuscript.

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    a

    Anoop Misra, M.D., was supported in part by a financial grant from the Department of Science and Technology, Ministry of Science and Technology, Government of India.

    b

    Om P. Ganda, M.D., was supported in part by grants DK 60115-02 and HL73168-02 from the National Institutes of Health.

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