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How does international migration influence individual and population health?

Concerns regarding the impact of international migration have featured prominently in recent public and political discourse. The outcome of the Brexit referendum in the UK, and the election of Donald Trump were, in part, seen as a response to growing fears related to the impact of immigration. While migration is not new, the number of international migrants has risen over recent decades due to voluntary and involuntary factors including increasing globalisation, international transport, communication, and the impacts of climate change.[1] International migrants are a diverse group, who face a variety of health risks. Understanding the challenges facing this population is important for improving the health of migrants and the populations of both the origin and destination countries.

The UN recently estimated that 244 million people live in a country other than where they were born, a 41% increase over the previous 15 years.[2,3] People migrate, voluntarily or involuntarily, for diverse social, environmental, political, economic or humanitarian reasons. Many migrants choose to move voluntarily for economic opportunities; others are forced to migrate due to natural disasters, conflict or persecution. Obtaining accurate statistics on the number of international migrants is difficult due to the different definitions used, and practical challenges in tracking undocumented or irregular migrants (see below).

The relationship between migration and health is complex and varied. Health may improve if migrants move to a country where access to health care and economic opportunities are better than their country of origin.[2] On the other hand, migrants’ health status may worsen if they are exposed to poor living and working conditions or encounter barriers accessing the host country’s health care system.[4] Migrant health is also influenced by a range of genetic, social and environmental determinants that may persist for generations.[2] The health of migrant populations also tends to converge towards that of the host population as individuals begin to adopt the health behaviours and lifestyles of their new country.

While migrants tend to be a selective group, representing individuals healthy enough to travel, they also face unique health challenges. Migrants from countries with endemic infectious diseases may be asymptomatic carriers or at an increased risk of infection.[5] Women, children, irregular migrants and trafficked persons are particularly vulnerable and at an increased risk of physical and sexual violence.[1] Additionally, the mental health burden often appears to be greater for migrants than the host population, particularly among refugees and asylum seekers. Health systems in destination countries need to recognise the specific health challenges facing migrant populations and implement policies to reduce barriers to health care. Such barriers not only go against the UN’s Sustainable Development Goals, which advocate for universal access to health care, but they also put the health and well-being of the host population at risk.

With the number of international migrants increasing at a faster rate than global population growth, there is an urgent need to provide an evidence base to inform public discourse and policy.[3] As part of this, our team will be contributing to the University College London – Lancet Commission on Migrant Health.[2] This commission is working to collate and analyse all available evidence on the health of individuals and populations, and the impact on country health systems, as well as producing new empirical work on these themes. It will also provide policy recommendations to “maximise the benefits and reduce the costs of migration on health locally and globally”.[2] We hope that our findings will be available towards the end of the year.

Definitions of international migrants

  • International migrants: Individuals who remain outside their usual country of residence for at least one year.

  • Irregular (or undocumented/illegal) migrants: Individuals who enter a country, often in search of employment, without the required documents or permits, or who overstay the authorised length of stay in the country.

  • Trafficked persons: Individuals who are coerced, tricked, or forced into situations in which their bodies or labour are exploited, which may occur across international borders or within one country.

  • International labour migrants (flow): Individuals engaged in a paid activity in a state of which he or she is not a national, including persons legally admitted as a migrant for employment.

  • Refugees: Individuals who, owing to a well-founded fear of being persecuted for reasons of race, religion, nationality, membership of a particular social group, or political opinion, are outside the country of their nationality, and are unable to, or owing to such fear, are unwilling to avail themselves of the protection of that country or return because of fear of persecution.

  • Asylum-seekers: Individuals who have sought international protection and whose claims for refugee status have not yet been determined.

  • Stateless persons: Individuals not considered as citizens of any state under national law. Covers de jure and de facto stateless persons, including persons who are unable to establish their nationality. Stateless persons may or may not be migrants.

  • Tourists: Individuals travelling to and staying in places outside their usual environment for not more than one consecutive year and whose main purpose of visit is other than work.

  • International students: Individuals admitted by a country other than their own, usually under special permits or visas, for the specific purpose of following a particular course of study in an accredited institution of the receiving country.

Adapted from Zimmerman et al. (2011).

Anna Louise Barr is a PhD student in the Department of Medicine at the University of Cambridge.

Sean Bartlett is PhD student in Chemistry, also at the University of Cambridge.


[1.] Zimmerman C, Kiss L, Hossain M. Migration and health: a framework for 21st century policy-making. PLoS medicine. 2011;8(5):e1001034.

[2.] Abubakar I, Devakumar D, Madise N, Sammonds P, Groce N, Zimmerman C, et al. UCL-Lancet Commission on Migration and Health. The Lancet.388(10050):1141-2.

[3.] Harrigan F S-MS. 244 million international migrants living abroad worldwide, new UN statistics reveal: United Nations Department of Public Information; 2016 [cited 2017 13th June]. Available from:

[4.] McKay L MS, Ellaway A. Migration and health: a review of the International literature. Glasgow: MRC Social & Public Health Sciences Unit; University of Glasgow, 2003 Contract No.: No. 12.

[5.] Aldridge RW, Yates TA, Zenner D, White PJ, Abubakar I, Hayward AC. Pre-entry screening programmes for tuberculosis in migrants to low-incidence countries: a systematic review and meta-analysis. The Lancet Infectious diseases. 2014;14(12):1240-9.


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