Migration and health: a review of the international literature

s for each of the 362 papers were retrieved and read by three researchers. From this, a further list of inclusion and exclusion criteria was drawn up, to reduce the number of studies to be reviewed and to limit the range of health issues under consideration. The following inclusion criteria were used: must be primary empirical studies; must focus on actual migrants who make the move, not second generation, siblings, or ethnic groups established within countries; must have a control group, i.e. compare migrants to either the host population or the population in the country or region from which they migrated must be quantitative Studies focusing on the following groups and health related outcomes were excluded: migrant farm/agricultural workers return migrants refugees/asylum seekers health related behaviour (smoking, diet and exercise) learning disabilities physical disabilities mental health admissions access/use of health care Opinion pieces and review articles were excluded, while papers on physical and mental health, all cause and cause specific mortality, physical development and functioning (birth weight, height, Blood Pressure etc.) were included. The 362 abstracts were re-read by three researchers in the light of these inclusion/exclusion criteria, resulting in the selection of 136 papers which met all criteria. Each of these selected papers was retrieved and read in full by a single researcher to ensure inclusion was merited. Exclusion was decided by at least two researchers. Each paper in turn was analysed by a single researcher extracting information on the following areas onto a standard form (see section 6) with the following fields: aim of the study country of origin (of the study) health outcome migration details (from, to, and type) sample size age distribution gender distribution ethnicity comparison group factors controlled for methods time factor (year of migration) results/findings/conclusions The papers were then grouped into five areas: Internal Migration MRC Social and Public Health Sciences Unit Page 4 Occasional Paper Number 12 International Migration: All cause and cardiovascular mortality International Migration: Cancer mortality International Migration: Mental health International Migration: Morbidity, risk factors and anthropometry The summaries of each study are reproduced in section 6, grouped as above. Section 3 gives a narrative summary. MRC Social and Public Health Sciences Unit Page 5 Occasional Paper Number 12 3 Summary 3.1 Internal Migration Migration within a country is known as internal or inter-regional migration. The aim of this research is to study geographical variation and determine which is the stronger predictor of a health outcome: ‘place of birth’ or ‘place of residence’. There is also interest in the effects of coming from a high to low risk area or vice versa, or moving from a rural to an urban area. Moreover, ‘selective migration’ is an important factor which is considered within many of the studies. Many studies investigate internal migration within Italy, due to known differences in mortality/morbidity between the North and the South, for example, higher rates of cancer deaths in the North. Several studies show that ‘area of birth’ is often a more important determinant of cancer rates than ‘area of residence’. This was found to be true for cancers of the mouth, pharynx, oesophagus, larynx, stomach, bladder (Vigotti et al., 1988), in addition to lung cancer (Buiatti et al., 1985) and colorectal cancer (Fascioli et al., 1995). Women from the South benefit from a ‘protective effect’ in terms of retention of a lower incidence of breast cancer mortality even after migration to the North. This advantage may be due to genetic factors or the retention of certain dietary practices, since associations have been found between breast cancer and body size, and daily intake of fat, in particular saturated fat, and alcohol consumption (Toniolo et al., 1989). It is apparent that various environmental factors and/or genetic elements influence the mortality rates of different cancers after migration, and such effects are not only apparent between the North and the South, but between provinces in Italy of varying risk. Ceppi et al. (1995) investigated the ‘province of birth’ as a risk indicator for lung and stomach cancer mortality among Genoa residents born in other Italian provinces. They discovered that for lung and stomach cancer, migrants originating from high-risk areas display higher risk than Genoa natives. Dietary habits in the first years of life may have induced an increase of absolute risk which could not be reversed by successive dietary changes. In other words, changes in habits and health behaviours after migration would not necessarily cause changes in mortality and morbidity rates. In seeking to explain mortality or morbidity rates in migrants, it may be important to consider not only certain behavioural factors, such as diet and smoking status, but also ‘socioeconomic status’ (SES). Barbone et al. (1996) studied cancer mortality amongst Italian migrant females moving to Northern Italy, to investigate the influence which ‘place of origin’ and SES (measured by occupation and education) exert upon breast cancer. Those who came from low risk areas remained at relatively low risk if subsequent migration occurred in adulthood. Barbone et al. argued that the determinants of the association between breast cancer and SES and geographical origin remain largely obscure. However, since education, professional achievements and geographical origin are closely related to conditions of the subject and of her family early in life, the findings indirectly support the hypothesis that factors which act at an early age play an important role in the aetiology of breast cancer. Similar studies to the Italian papers exist within the settings of the UK and the US. Coggon et al. (1990) observed that stomach cancer varied from place to place within England and Wales (E&W) and sought to find out which was the stronger influence, ‘place of birth’ or ‘place of death’. They found that proportional mortality from stomach cancer was more closely related to county of birth. This association was found in migrants both out of, and into, high-risk areas. On the other hand, place of death may exert a strong influence on specific conditions, with the low risk of stroke associated with living in Greater London being acquired by individuals from other regions of E&W who move there (Strachan et al., 1995). Elford et al. (1990) found that regional variations in the UK in Blood Pressure were strongly influenced by where the men had lived for most of their adult lives, rather than by where they were born and brought up. An appreciable geographic gradient in both systolic and diastolic MRC Social and Public Health Sciences Unit Page 6 Occasional Paper Number 12 BP was apparent in the males. Irrespective of where they were born, men living in Southern England showed lower mean BP than those living in Scotland. Studies in the US are often based on known differences in mortality/morbidity between Southern and Northern States. Striking differences in cancer mortality were found between southern-born blacks who moved to New Jersey (NJ) and those born in NJ (Greenberg and Schneider, 1995). Southern-born black male and female migrants had an all-cancer mortality rate 31% and 10% higher, respectively, than their NJ counterparts. The Southern-born showed significantly higher rates for cancer of the cervix, oesophagus, male lung, prostate and stomach than the NJ-born. In contrast, low rates were evident among foreign-born blacks in NJ. Similarly, a study of Ohio residents by place of birth identified an increased cancer risk among black migrants born in the South compared with Ohio-born Blacks. The author maintains that genetics and poverty and malnutrition endemic in the early years of life, provided Southern-born individuals with the basis for increased susceptibility to ill health (Mancuso, 1977). Various studies have investigated movements between rural or traditional areas and urban areas within a country. These rural-to-urban migration studies often focus upon the potential negative effect, physically and/or emotionally, not only of the stress of movement and adaptation to a new and very different lifestyle, but of movement to an area with more health damaging exposures. The area may be less healthy in terms of factors relating to the physical environment, socio-cultural environment, and health behaviours. Verheij et al. (1988) suggests that urban populations in the Netherlands reported more health problems, suffered more frequently from chronic conditions, and more often considered their health status to be “less than good”. Although change is common to all kinds of internal migration, it is particularly pronounced in rural to urban movement. Luo tribe members moving from rural land in Western Kenya to urban Nairobi, displayed an increase in mean systolic Blood Pressure (BP) after migration, and exhibited a greater prevalence of hypertension, than tribe members who did not migrate (Poulter et al., 1990). Similarly, migrants moving from South Western rural China to the urban area of Xichang City showed an increase in serum total cholesterol lipid levels which could lead to elevated coronary heart disease risk (He et al., 1996). This increase may result from a diet higher in saturated fats and lower in fibre, combined with alcohol consumption, cigarette smoking and physical inactivity. Torun et al. found that high proportions of young Guatemalan women in rural and urban areas are overweight and sedentary, and that migration to a city further augments sedentarism and undesirable eating habits among both men and women. Moreover, rural-to-urban migrants in developing countries experience higher child mortality after settling in cities, than do lifelong urban residents. This may be due to concentration of migrant