Today more and more people are migrating to other countries, and international migrants currently account for 3% of the world population . Global migration is a complex phenomenon that draws on a multiplicity of health, economic, social and security aspects in an increasingly interconnected world. Although migration, accepted and established in many countries, has become an avenue to economic well-being, the resulting variation in population has drastically increased disease rates . Several mechanisms connected to the individual histories of migrants have been explained for the differences in health status between immigrants and natives. The healthcare habits and lifestyles of immigrants may be marked by the original ones learned their country of origin mixed with those acquired by acculturation in their host country, a phenomenon that increases with the duration of the stay. Despite the general public interest, the increased risk for diseases  and the likely impact on public health systems in destination countries , the literature on immigrant health status remains scarce and provides contradictory results .
An increase in morbidity and mortality among immigrants, as compared to that for natives, has been described for a wide spectrum of diseases, among them cardiovascular ones. As a reliable marker, blood pressure (BP) is used to assess the impact of changing domiciles, as it responds quickly to migration . In addition, hypertension (HTN), a very prevalent and costly condition, is considered a good indicator of the overall well-being of particular population groups across countries . Although high BP is increasing in prevalence in children and adolescents, because of the obesity epidemic, the importance of BP goes beyond its relation to obesity. Longitudinal studies have revealed a relation between childhood BP and future BP values in young adults independent of BMI . In a previous study, BP at adolescence linearly predicts progression to HTN in young adulthood, even in the low-normotensive range . Given that adolescents with high BP are likely to become adults with HTN, with the consequent HTN-induced organ damage, the impact will be substantial. Even when the relation between BP in youths and future HTN is very well known, the economic burden of high BP in children and adolescents worldwide has not yet been evaluated.
Despite the potential benefits of knowledge about high BP at a young age, information on the impact of immigration on HTN in youth is practically absent from the literature. Filling the gap, in the current issue of the Journal of Hypertension, Peled et al. present a study carried out in Israel with a remarkable cohort size, 2.7 million adolescents. Their study assesses the association between immigration and age at immigration with the prevalence of HTN at 17 years of age. The age at immigration addresses the entire pediatric age, from 0 to 19 years, with different BMI categories and countries of origin.
The results revealed that despite a very low prevalence of HTN, those born in Israel had a lower HTN crude prevalence as compared with study participants immigrated. Those aged 12–19 years at immigration had a lower prevalence of HTN in a fully adjusted analysis for factors influencing BP values such as weight status, age and sex. These differences were still present when the country origin was taken into account. In parallel with the differences in risk of HTN, the recent immigrants exhibited lower rates of overweight (8.1%) and obesity (3.4%) than did those Israeli-born, in which overweight was 9.1% and obesity 4.5%.
In this study, a very low prevalence of HTN has been reported, similar to that described by Lo et al. but lower than the prevalence in previous studies from Europe and the United States [11,12]. The prevalence of pediatric HTN worldwide is not known, because of regional differences in the definition of HTN, the distribution of reference BP data and the BP measurement methodology . The main reason for the low prevalence in the present study is that the diagnosis was based on multiple office BP measurements as the European Society of Hypertension Guidelines in Children and Adolescents  clearly state. In fact, a child should not be diagnosed with HTN until he or she has shown evidence of sustained BP elevation. An additional factor to explain the low prevalence of HTN is the low number of overweight and obese study participants, less than half the figures seen in Europe .
The potential factors responsible for BP elevation in immigrants need to be taken into consideration. The lifestyle and healthcare habits of immigrants may be marked by habits adopted in their country of origin that they will lose progressively as they adopt the habits of the host country. This process intensifies in relation to the duration of their stay. The most relevant acculturation factors with a negative impact on health are stress, low levels of physical exercise and changes in diet. Immigration to affluent societies with richer and more varied diets is often associated with increased fat and sodium intake and lower physical activity. Whether or not the higher prevalence of HTN in those migrants arriving at early age is because of more years of exposure, to acculturation or whether it is a consequence of exposure in a more vulnerable period of their lives is a matter of interest. The attendant lifestyle changes become major predisposing factors for developing HTN, and there is little doubt that without intervention high BP in childhood will increase the risk of premature cardiovascular disease.
A matter of interest derived from the study is to see if looking at the health gap between immigrants and natives across host countries is a relevant issue. It may be attributed to cross-country differences in health status because of either differences in health selection at migration or to differences in the opportunities of integration of immigrants across countries. Specific migratory history or more restrictive legal framework for immigration may explain stronger health selection at migration in some countries . The advantage of the Peled et al.'s study is that it was conducted in the same host-country including data from the last five decades. Based in the same host-country, migrants from different origin countries have shown relevant differences. The immigrants from the former USSR and from Ethiopia who arrived in Israel during early childhood had higher odds ratios (OR) for being overweight or obese compared with those migrating in late childhood and adolescence. Similarly, graded increase in OR for HTN with decreasing age at immigration was observed in all origin groups except for immigrants arriving from Western countries. The reasons for these differences are based on the health and social conditions of the country of origin and the impact of acculturation.
The necessity of a tailored approach to improving the healthcare of immigrants should be stated. Determining the healthcare needs of specific immigration groups should lead to the establishment of evidence-based guidelines for providing screening and healthcare services to immigrant populations, not only for the benefit of the individuals concerned but also for that of the host countries . This can be especially relevant in the case of childhood and adolescence, periods characterized by growth and maturation. High BP is a clearly established, but modifiable, risk factor for early disability and death. Prospective studies are needed to better understand how acculturation influences health behaviors across different immigrant racial/ethnic groups. Intervention studies that test tailored strategies to improve lifestyle behaviors across specific diverse groups of immigrant are required.
Immigrant studies can provide some insights into the impact of lifestyles on cardiovascular risk and their interaction with genetic factors. The differences seen in various populations as they acclimate to new societies provide a window into the relevance of environmental factors in the development of cardiovascular risk factors and their consequences. Today it is well established that BP values depend on the interaction among genetics, environmental and fetal factors. The impact of each one of these factors in the population as a whole and in the individual study participant differs greatly. An improved knowledge of each factor can help to design actions that reduce the risk of high BP. Although genetics cannot be modified, fetal factors can be improved by controlling the mothers’ pregnancy and avoiding toxic exposure to substances like tobacco, alcohol and drugs. Several studies  are confirming the importance of a mother's nutritional condition at the moment of conception in determining the immediate and lifelong health of her baby. The longer term effects are those described by the developmental origin of the adult health and disease hypothesis. In contrast, environmental factors are multiple, including diet, physical exercise, social structure, pollution and others not yet well recognized. Studies performed in immigrants are a window of opportunity to assess the relevance of lifestyle factors, their duration and, more importantly, in which period of life the exposition occurs.
Migration is an increasing phenomenon driven by different factors. The huge impact on the health status of immigrants and the mounting burden on healthcare systems of the host countries require more careful attention be paid to them. Nevertheless, there are multiple impediments to appraising the information. This is a result of the multiple and varied racial, cultural and socioeconomic characteristics of the migrant population, the toughness found in the country of reception and, consequently, how the acculturation is produced. Future studies should be performed to obtain more precise information on the behavior of the migrant population. Still, these will address specific situations found in each country, and information and experiences in specific countries cannot be generalized, although a few relevant issues can be extracted from them. Studies like that of Peled et al. have contributed to a better understanding of this complex phenomenon in Israel and abroad.
Conflicts of interest
There are no conflicts of interest.
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