ReviewMigration and its impact on adiposity and type 2 diabetes
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.