Duration of residence and disease occurrence among refugees and family reunited immigrants: test of the ‘healthy migrant effect’ hypothesis

Objectives The ‘healthy migrant effect’ (HME) hypothesis postulates that health selection has a positive effect on migrants' health outcomes, especially in the first years after migration. We examined the potential role of the HME by assessing the association between residence duration and disease occurrence. Methods We performed a historical prospective cohort study. We included migrants who obtained residence permits in Denmark between 1 January 1993 and 31 December 2010 (n = 114 331). Occurrence of severe conditions was identified through linkage to the Danish National Patient Register. Hazard Ratios (HRs) were modelled for disease incidence by residence duration since arrival (0–5 years; 0–10 years; 0–18 years) adjusting for age and sex. Results Compared with Danish‐born individuals, refugees and family reunited immigrants had lower HRs of stroke and breast cancer within 5 years after arrival; however, HRs increased at longer follow‐up. For example, HRs of stroke among refugees increased from 0.77 (95% CI: 0.66; 0.91) to 0.96 (95% CI: 0.88; 1.05). For ischaemic heart disease (IHD) and diabetes, refugees and family reunited migrants had higher HRs within 5 years after arrival, and most HRs had increased by end of follow‐up. For example, HRs of IHD among family reunited migrants increased from 1.29 (95% CI: 1.17; 1.42) to 1.43 (95% CI: 1.39; 1.52). In contrast, HRs for TB and HIV/AIDS showed a consistent decrease over time. Conclusion Our analyses of the effect of duration of residence on disease occurrence among migrants imply that, when explaining migrants' advantageous health outcomes, the ruling theory of the HME should be used with caution, and other explanatory models should be included. Objectifs L'hypothèse de “l'effet du migrant en bonne santé” (EMS) postule que la sélection de la santé a un effet positif sur les résultats de santé des immigrants, en particulier dans les premières années après la migration. Nous avons examiné le rôle potentiel de l’EMS en évaluant l'association entre la durée de séjour et la survenue de la maladie. Méthodes Nous avons réalisé une étude prospective de cohorte historique. Nous avons inclus les immigrants qui ont obtenu un permis de séjour au Danemark entre le 01 janvier 1993 et le 31 décembre 2010 (n = 114 331). La survenue de conditions sévères a été identifiée grâce aux liens avec le registre national danois des patients. Les rapports de risque (HR) ont été modélisés pour l'incidence de la maladie selon la durée