Immigrants in Norway have lower all-cause mortality than natives, but their mortality differs depending on reason for migration, length of stay, and age at migration. As such, our findings are consistent with much international research. However, there are also some differences. In Norway, female and male immigrants have roughly the same relative survival advantage, in contrast to findings from for instance the US  and Denmark . As the differences between male and female life expectancy in the host populations are roughly similar (4–5 years at birth) in the US, Denmark and Norway, and the ratios of male to female immigrants roughly equal (about 50%), we are unable to explain why our results differ from that of others. Consequently, sex differences are not discussed further.
Selection in out-migration
As stated in the theoretical framework, immigrants are not a representative sample of their countries of origin. They often tend to be above average resourceful [2, 3], which may explain the relatively weak impact of sending countries’ HDI on death risks. In line with this, our results suggest that reason for migration appears to matter more. The difference in mortality among immigrants from various areas of origin is most pronounced for refugees and family migrants – while there is more consistency in mortality for labor and education immigrants across areas and individual countries.
Health selection, that migrants are either healthier or sicker than the average in the sending country, is one explanation. Our findings support an overall ‘healthy migrant’ selection, in line with results of others [4, 5]. Healthy people will move for work or education , as is supported by our results which show that immigrants who come to Norway for education and/or labor have the lowest mortality, while refugees and family immigrants to refugees had a higher mortality, though lower than native Norwegians. Our findings align well with a recent Norwegian study on immigrants’ health, finding that labor and education immigrants have better health than refugees and family immigrants , and studies which find that the same is true for primary health care utilization  and hospitalizations . Since the Nordic countries have comparable welfare systems related to health, education and income, we find it reasonable that the Nordic immigrants in Norway have similar mortality as native Norwegians.
On the other hand, certain groups of immigrants may have poorer health and higher mortality than the general population [33, 38]. This has been explained by stress, trauma and other adverse health exposures related to the migration process, such as changes in social status  or conditions related to ‘forced’ migration, often characteristic for the situation of refugees [9,10,11]. Last, some sick people will move in hopes of getting better treatment in a new country [7, 8]. However, regardless of reason for migration, no evidence of worse health was found in the present study, and our results thus suggest that the ‘healthy migrant’ selection undermines any such effect, particularly in the short run.
In both Denmark and Sweden, immigrants generally have the same relatively low mortality as immigrants in Norway [10, 41]. However, the risk of dying varies between different immigrant groups, and unlike what we find in Norway, some immigrant groups in the other Nordic countries have equal or higher mortality [10, 33].
Immigration to Norway has shifted considerably over time. This applies both for reason for migration, timing, and the countries (areas) people migrate from. This makes it difficult to distinguish the importance of reason for migration, age at migration, proportion of life spent in Norway and/or place of origin. When we compare findings across these factors, we find some differences: For refugees, mortality is lowest for those who migrated at a young age, before it increases with increasing lengths of stay. The opposite pattern is seen for family immigrants: Mortality is lowest for those who migrate at older ages and then drops with increasing lengths of stay. As such, the positive selection of adult immigrants may not fully extend to include their children or younger family members. It may thus be relevant to take the reason for migration or underlying factors that are associated with the migration into consideration in the analysis of the importance of length of stay and age at migration, especially as immigrants gain experience in a host country. For immigrants with relatively short lengths of stay in Norway, all groups, regardless of the reason for migration, have significantly lower mortality than natives. This may suggest an initial positive health selection .
Selection in return-migration
According to the theoretical framework, immigrants may choose to return to their countries of origin when they get sick or old, to die in their country of origin . In the United States, privatized health care might be a driver for this hypothesis [13, 14]. In the Nordic countries, virtually free public health services are available for all. As the risk of death increases with length of stay, our findings do not support selective re-migration of sick individuals, in line with results from for instance Denmark and the Netherlands [15, 16].
Integration, cultural adaption and health
There is considerable variation in the extent to which immigrants become integrated in the host society , including the extent to which they adapt lifestyle factors that promote or reduce their health [21, 45]. As we rely on mortality data as a proxy for health, we are unable to shed light on whether Norwegian immigrants’ lower use of health services reflect a better health or an underuse of health services. Below we attempt to discuss mortality patterns by length of stay and age of migration to hypothesize whether the lower mortality we observe among immigrants may be a result of their health being better than that of the host population.
Length of stay and age at migration
We find that the mortality of immigrants increases with prolonged lengths of stay. This conflicts with some findings [4, 38, 39], but is concordant with the hypothesis of adverse adaptation and consistent with findings from others [36, 37]. It is also consistent with the impact of migration as an independent determinant of health and with a ‘social causation’ interpretation, i.e. that immigrant status interacts with sociodemographic disadvantages as conventionally measured, and thus increases mortality . Immigrants with long lengths of stay were pioneers when they arrived, and any positive health selection effects may over time have been offset by long exposure to Norwegian societal structures, habits and risk factors.
Immigrants who arrive in Norway at very young ages have lower mortality than other groups of immigrants. It may be argued that immigrants who arrive in Norway in early childhood will be less affected by being immigrants . However, immigration during childhood and adolescence might be detrimental for health, since they show similar mortality levels as natives. Another possible explanation is that the selection bias during infancy is different depending on the age of the child, with the youngest being more susceptible to death in their home countries or during migration. In accordance to our findings, lower mortality was also observed among immigrants in the US and France who arrived at higher ages, regardless of duration of residence [13, 39, 40, 44], in line with the hypothesis of positive health selection .
The share of life spent in Norway attempts to simultaneously measure both length of stay and age at migration. Our findings show that mortality is low for immigrants who have lived only a small share of their lives in Norway, before it rises markedly, thus supporting the hypotheses of positive health selection, unfortunate social adaptation, as well as ‘social causation’ and allostatic load, or the health burden of chronic stress, related to migration .
Limitations and future research needs
Although this is a national study with long follow-up and relatively detailed and complete data, several limitations exist: Firstly, registrations of immigrants’ emigration are less complete than for natives. This is problematic because immigrants have greater emigration rates than the majority: In 2011, around 70% of all emigrations concerned immigrants . Furthermore, emigration probabilities depend on the reason for migration, length of stay and age at migration. We know that labor and education immigrants often spend only a short period in Norway. An alternative explanation for positive health selection for the low mortality we find for these groups may thus be missed emigration registrations. In our calculations of risk of death according to these characteristics, we did not detect evidence for consistent misclassifications in a specific direction, and as the risk of death increased with increasing length of stay, we conclude that possible missed emigration registrations are unlikely to drive our results. This is of critical importance since consistent errors in emigration registrations would make immigrants ‘immortal’ in a statistical sense , causing immigrants’ mortality to be incorrectly estimated too low.
Secondly, the immigrants included are relatively young because of Norway’s relatively short history of immigration. As such, the deaths we use in the analysis are relatively unevenly distributed for the characteristics under investigation resulting in some unstable estimates. As further research accumulates, our findings may be rebutted.
Thirdly, information on cause of death would have given us a better indication of health disparities, but this information is unfortunately not available and due to the young age of the immigrant population the numbers in the respective subgroups would be small.
Lastly, and most importantly, we lack information on health. Not all health differences translate into mortality differences. Furthermore, some mortality differences (albeit rare) may not relate only to health, such as for instance work accidents. As such, a more proximate measure of health could have given us more policy relevant information. This pertains both to immigrants’ health prior to arriving in Norway, and their health trajectories once in Norway. In general, information on immigrants’ health during their life course in Norway is only available from cross-sectional surveys based on self-selected samples. Knowledge of immigrants’ health prior to arrival in Norway is scarce and mostly anecdotal.
Norway and the other Nordic countries are welfare states with affordable and available health care and income security, resulting in less inequality across various areas of health than in many other countries. However, as we find that the risk of death is low initially, before it increases substantially with increasing length of stay, welfare policies may not successfully benefit immigrants in the long run. Unfortunately, we did not have access to the characteristics of immigrants before they leave their country of origin . However, our results of low mortality shortly after arrival may support the ‘healthy migrant’ hypothesis, perhaps suggesting that the health of migrants prior to migration may be better than the health of the general population in both the sending and the receiving country. On a similar note, we used the most recent United Nations’ HDI measure available for each country, irrespective of the migrants’ year of emigration. It would likely have been more optimal to use the HDI at migrants’ time of emigration from their country of origin. Unfortunately, this date is not available in our data. However, since the majority of the HDI measures have been relatively stable from 1990 onwards for sending countries of the largest immigrant groups in Norway, we believe it is unlikely that a different coding would majorly impact on our results.
Whether our findings may be generalized to countries with dissimilar welfare systems, especially health care systems, remains to be examined, and comparative research in this area is currently largely lacking [49, 50].