Human migration, the movement of people from one place in the world to another, has gone on for time immemorial being one of the earliest social phenomena history records. In animals it is a ubiquitous phenomenon—found in all major animal groups—and triggered most commonly by climate, availability of food, the season of the year or mating reasons. Ultimately, the innate desire to seek pastures new and to better one's lot is a survival instinct and thus is ironic considering how (im)migration is a political football in these times. However, whereas earlier human migrations usually involved moving into areas that were uninhabited, human migrants now tend to move to areas already settled and thus may result in conflict with indigenous people and cultures of that area.

Migration started to interest epidemiologists, and in particular cardiovascular epidemiologists, as the disease took hold in richer parts of the world during the middle of the 20th century. The NIHONSAN Study, a prospective cohort, was one such example. It compared three groups of Japanese men living in Japan, Hawaii and the Bay Area of California, and assessed their distribution of coronary disease incidence and mortality. Japanese people had begun migrating to the USA in significant numbers following the political, cultural and social changes stemming from the 1868 Meiji Restoration. In the study, Japanese men living in the Bay Area of California experienced higher coronary disease incidence than those in Hawaii and Japan.1 One would think a migrant, for all the traumas involved in their upheaval, would expect a better life in new pastures. Such work started to untangle the downsides to migration.

The bigger human migrations in recent times are, however, not across oceans, but within country from rural to urban areas. With ever greater political hurdles to international migration and the increasing economic …