An investigation of the healthy migrant hypothesis: Pre-emigration characteristics of those in the British 1946 birth cohort study.

OBJECTIVES The finding that migrants to high-income countries have lower rates of morbidity and mortality than non-migrants, controlling for socioeconomic position, is often attributed to the "healthy migrant" hypothesis, which suggests that only the healthiest individuals choose to migrate. This prospective study investigates the healthy migrant hypothesis in a cohort of British emigrants using pre-migration health indicators. We also investigate how early-life health characteristics relate to age at emigration and whether or not the emigrant returned home. METHODS Data are from the Medical Research Council National Survey of Health and Development, a nationally representative cohort study of people born in England, Scotland or Wales in March 1946. Childhood socio-economic position, health and cognitive ability were compared between 4,378 non-emigrants and 984 emigrants. Of the emigrants, 427 emigrated before age 20 and 557 after that age; 602 emigrants remained abroad and 382 returned home. RESULTS Emigrants had better childhood health (especially greater height), higher childhood socio-economic position and better childhood cognitive ability at age 8 than non-emigrants. Return emigrants were very similar to emigrants who remained abroad. CONCLUSIONS We found support for the healthy migrant hypothesis in a cohort of British emigrants. Our findings improve an understanding of how health is distributed within and across nations.