Ethnic differences in obesity among immigrants from developing countries, in Oslo, Norway

Abstract

Objectives:

To compare ethnic and gender differences in generalized and central obesity and to investigate whether these differences persisted after adjusting for socio-demographic and lifestyle factors.

Design:

In 2002, the population-based cross-sectional, Oslo Immigrant Health study was conducted.

Subjects:

A total of 7890 Oslo residents, born between 1942 and 1971 in Turkey, Iran, Pakistan, Sri Lanka and Vietnam, were invited and 3019 attended.

Measurements:

Participants completed a health questionnaire and attended a clinical screening that included height, weight, waist and hip measurements.

Results:

Generalized obesity (BMI30 kg/m2) was greatest among women from Turkey (51.0%) and least among men from Vietnam (2.7%). The highest proportions of central obesity (waist hip ratio (WHR)0.85) were observed among women from Sri Lanka (54.3%) and Pakistan (52.4%). For any given value of BMI, Sri Lankans and Pakistanis had higher WHR compared to the other groups. Despite a high mean BMI, Turkish men (27.9 kg/m2) and women (30.7 kg/m2) did not have a corresponding high WHR. Ethnic differences in BMI, waist circumference and WHR persisted despite adjusting for socio-demographic and lifestyle factors.

Conclusion:

We found large differences in generalized and central obesity between immigrant groups from developing countries. Our data find high proportions of overweight and obese subjects from Pakistan and Turkey, but low proportions among those from Vietnam. Subjects from Sri Lanka and Pakistan had the highest WHR for any given value of BMI. Our findings, in light of the burgeoning obesity epidemic, warrant close monitoring of these groups.

Introduction

The global obesity epidemic, marked by alarming proportions in affluent countries and increasing numbers in some developing countries, raises several concerns.1, 2 This burden of obesity is not shared equally by all segments of society and varies by ethnicity.3

Obesity exhibits both genetic and environmental associations, suggesting individual susceptibility that interacts with adverse environmental conditions. While the exact causes of obesity remain to be fully elucidated, associations with demographic, socio-cultural, biological, behavioural and lifestyle factors have been observed.4, 5 The close linkage of obesity to type 2 diabetes and associations with a wide spectrum of morbidities make it one of the most important avoidable risk factors.6

While BMI is widely accepted as the measure of obesity, Deurenberg-Yap et al. among others have highlighted that some ethnic groups have higher body fat percentage (BF%) at relatively lower BMI.7, 8 Current literature supports evidence that immigrants are no exception to the obesity epidemic9 in the USA and Europe.10 However, European studies to date have been limited to few selected immigrant groups.

Immigration to Norway from developing countries, largest groups being from the Indian subcontinent and the Middle East,11 dates back only 30 years. Studies from countries of origin show fairly low levels of generalized and central obesity.12 However, to date, obesity among immigrants from developing countries in Norway has not been described in any detail.

The objectives of this paper are to analyse whether there are ethnic and gender differences in generalized and central obesity in five major immigrant groups, and furthermore to determine if these differences persist after adjusting for socio-demographic and lifestyle factors.

Subjects and methods

The population-based, cross-sectional, Oslo Immigrant Health Study was conducted by the Norwegian Institute of Public Health and the University of Oslo in 2002. Oslo residents, born in Pakistan, Sri Lanka, Turkey, Iran and Vietnam, were invited to attend. This study followed the Oslo Health Study (HUBRO 2000–2001), described in detail elsewhere (www.fhi.no), and both studies followed the same protocol. The Norwegian Data Inspectorate approved the study and it has been cleared by the Regional Committee for Medical Research Ethics.

Sample

From the 2001 population register, 7972 individuals (born 1942–1971) were eligible for participation, excluding those who had already participated in HUBRO (800 persons born in 1940, 1941, 1955, 1960 and 1970). Since 11 individuals had died and 72 had emigrated prior to the invitation, 7890 were eligible for participation but only 7607 were reached by mail. Of the 7607 reached by mail, 3019 attended a clinical screening, gave their written consent and met the criteria of inclusion (completion of at least one question in either of the questionnaires), attaining a final response rate of 39.7%. Participation rates according to country of birth are as follows: Turkey 32.7%, Sri Lanka 50.9%, Iran 38.8%, Pakistan 31.7% and Vietnam 39.5%, respectively. The nonresponder pattern among these groups was similar to that observed in the preceding Oslo Health Study, described in detail elsewhere.13

Data collection

Two weeks prior to the clinical screening the questionnaire, consent and information brochures and their appropriate translations were sent to participants. A single reminder was sent to nonresponders of the first invitation. Screenings, held at three local district stations, offered additional assistance of fieldworkers fluent in the five immigrant languages.

Anthropometry

Body weight (in kg, one decimal) and height (in cm, one decimal) were measured with an electronic Height and Weight Scale, with the participants wearing light clothing without shoes. BMI (kg/m2) was calculated based on weight and height. Both waist and hip were measured with a measuring tape of steel. Waist and hip circumference were used to calculate the waist hip ratio (WHR), using the formula waist (cm)/hip circumference (cm).

Questionnaire

The main questionnaire covered a wide range of issues, including general health status, self-reported disease, risk factors, as well as socio-demographic factors. The questionnaires were based on questions previously used for ethnic Norwegians, and were not validated for immigrants. The original questionnaires along with official English translations can be found at the following website: http://www.fhi.no/tema/helseundersokelse/oslo/index.html

Variables

The Norwegian Registry of Vital Statistics provided information on the age, gender, country of birth and residential address. Ethnicity was determined on the basis of country of birth from this register. A cross-check with Statistics Norway (SSB) registers confirmed that in 99.8% of cases the country of birth was identical to their ‘country of origin’.

Self-reported continuous variables included years of education, years lived in Oslo and number of children.

Respondents were asked about their smoking status; and their responses were categorized as: (1) yes, now (current smoker), (2) yes, earlier (previous smoker) and (3) never (nonsmoker).

Self-reported leisure-time physical activity was assessed by a four-graded measure (inactive to very active) shown to predict the mortality risk in both genders. Responses included: (1) ‘reading, watching television or other sedentary activities’ (inactive/sedentary); (2) walking, cycling or moving at least four times per week; (3) taking part in physical exercise/sport or heavy gardening; (4) hard exercise or participation in competitive sports regularly (very active).

Data analysis

Data were analysed using the SPSS package 11.0. We report gender-specific, age-adjusted descriptive statistics for BMI, WHR and waist circumference (WC). Means were compared by analysis of variance (ANOVA) and proportions by χ2 tests. Linear regression analysis, stratified by gender, explored associations between indices of obesity and ethnicity, adjusting for age, education, number of years lived in Oslo, smoking, number of children and physical activity.

Results

Sample characteristics

Background characteristics (Table 1) showed significant differences in age, with the Sri Lankans being the youngest and Pakistanis the oldest. Iranians were significantly more educated compared with all ethnic groups, the only exception being Sri Lankan women. Subjects from Turkey had the least education compared to all groups. Subjects from Pakistan had the longest length of stay in Oslo compared to those from Sri Lanka. Pakistani women had the highest parity compared to all ethnic groups. Over 45% of the respondents were sedentary, the greatest proportion being among Pakistanis. Smoking was least reported among Sri Lankans and most reported among the Turks.

Table 1 Background characteristics of adult immigrants from developing countries. Oslo Immigrant Health Study 2002

Anthropometric characteristics

After adjusting for age, Vietnamese men and women had the lowest mean height, whereas Turkish men and women had the highest mean weight (Table 2). BMI increased by age in all groups, except for the Pakistanis (Figure 1). After adjusting for age, the Vietnamese had the lowest BMI, whereas the Turks had the highest BMI for both genders (Table 2). All ethnic groups with the exception of Vietnam had a lower mean BMI for men than women. Mean WC was the greatest among Pakistani men and women. However, mean WHR was highest among Pakistani and Sri Lankan men and women.

Table 2 Age-adjusted anthropometric characteristics and age-adjusted obesity prevalence of adult immigrants
Figure 1
figure1

Mean BMI of adults from five ethnic groups (Oslo Immigrant Health Study, Norway).

Prevalence of obesity

A greater proportion of women were obese (BMI30 kg/m2) than men. Twice as many women from Turkey, Pakistan and Sri Lanka were obese compared to their men. The highest prevalence of obesity was among Turkish women (51.0%) and least among Vietnamese men (2.7%). Nearly 80% of Pakistanis and over 60% of Sri Lankans were found to have a BMI25 kg/m2. Central obesity measured by WHR was highest for Pakistani women (55.6%). Gender differences in WHR were greatest among the Sri Lankan men and women (8.6 and 51.3%).

Indices of obesity and associated factors

Despite adjustments for education, physical activity and smoking, the ethnic difference in BMI, WHR and WC between Vietnamese men and other ethnic groups (Table 3) persisted. These factors, including age, accounted for 14.6% (BMI), 22.6% (WHR) and 22.3% (WC) of the ethnic differences among men. In the case of women after adjusting, in addition to the other factors, number of children, ethnic differences persisted for BMI and WC between the Vietnamese and other groups, but only for Sri Lanka and Pakistan for WHR. These factors, including age, accounted for 27.9% (BMI), 18.7% (WHR) and 30.2% (WC) of the ethnic differences.

Table 3 Age- and multivariate-adjusted differencesa in BMI. WHR and WC between Vietnamese and other Immigrant groups

Relationship between the indices of obesity

After adjusting for age, positive associations between BMI and WHR were observed in all groups (Figure 2). For any given value of BMI, the mean value of WHR was higher in subjects from Sri Lanka and Pakistan compared to other groups (Figure 2). Despite having the highest BMI, Turks did not have corresponding highest values for WHR. Ethnic differences followed a fairly similar pattern for WC though differences were attenuated (Figure 3).

Figure 2
figure2

Association of WHR and BMI among adults from five ethnic groups (Oslo Immigrant Health Study, Norway).

Figure 3
figure3

Association of WC and BMI among adults from five ethnic groups (Oslo Immigrant Health Study, Norway).

Discussion

Our study has shown that immigrants in Oslo are no exception to the onslaught of the obesity epidemic. Generalized obesity was most frequent among the Turks, with one out of two Turkish women having a BMI30 kg/m2. However, central obesity was most frequent among the Pakistanis and Sri Lankans. For any given value of BMI, the WHR was considerably higher among Sri Lankans and Pakistanis compared to the other groups. Ethnic differences in BMI and WHR persisted despite adjusting for age, known socio-demographic, biological and lifestyle factors.

For the first time in Norway, we have been able to study and explore associations between actual anthropometric measurements and determinants of obesity among immigrants, from a considerable population-based sample (3000). The low participation rate (39.7%) cannot rule out possible self-selection. However, other researchers also report low attendance rates among marginalized groups, such as immigrants in large population surveys. In particular, accessing South Asian communities is difficult, and is a barrier to research.14

While one should be cautious in generalizing our findings to the entire population, it is unlikely that the large differences in obesity can be merely attributed to bias. Differences in prevalence of obesity between the Turks and the Vietnamese are so great that it is nearly inconceivable that they can be explained by selection bias. When comparing associations between the indices of obesity and risk factors between groups, selection bias will be less than when assessing prevalence estimates or population means of risk factors.15 A comprehensive analysis of the nonattendance in the Oslo Health Study (2000–2001, that preceded our study with the same protocol and similar dropout problem) showed that age, education, income and gender (women) were positively associated with attendance, and this also applied to non-Western immigrants in addition to the Norwegians. However, their analysis concluded that prevalence estimates were robust even in light of the considerable non-attendance.13

Norway's previously homogenous population has evolved to a multicultural society that needs to examine ethnic health inequalities. Few studies have investigated groups like the Vietnamese, Iranians and Turks in comparison to the South Asians. Age and gender differences of the ethnic groups reflect the historical perspectives of migration; Pakistanis came here first and are the oldest. Our data are also unique with regard to the most susceptible groups from South Asia. Previous studies have identified intra-ethnic subgroup differences as a limitation to inferences of data obtained, due to the heterogeneity of risk factors.16 In our study, the majority of immigrants from Pakistan (Punjabi) and Sri Lanka (Tamil) originate from one major ethnic group and therefore intra-ethnic differences have been considerably reduced.17

The prevalence of obesity (BMI30 kg/m2) among Pakistani women (39.8%) is four times higher than Norwegian Women (11.6%).18 Immigrant women from developing countries might be more traditional with regard to parity, physical activity, smoking and employment compared to Norwegian women. The anthropometric means (BMI, WHR and WC) among the Pakistanis are identical to the Riste et al.'s19 findings from Manchester in an urban but much smaller sample. Nevertheless, the mean BMI of Pakistani women (29.3 kg/m2) in our study is much higher than in a study from Pakistan (21.9 kg/m2).12 A study from Turkey reported lower prevalence of obesity (39.3%)20 than our sample.

If the recently21, 22 proposed WHO definitions23 are applied, an overwhelmingly large majority of the Pakistani men (77.1%) and women (80.4%) are obese (BMI>25 kg/m2), and 78.2% are overweight (BMI>23 kg/m2). While BMI cutoffs underestimate BF% in these groups, WHR has shown the strongest association with diabetes across the ethnic groups, confirming the limitation of using the BMI for this purpose.24

Ethnic differences in BMI persisted after controlling for socio-demographic and lifestyle factors. Migration is synonymous with change of living conditions, status in life and lifestyle. During migration, professional status enjoyed in the home country is often lost as education is not recognized by the host country. Immigrants from Pakistan and Turkey originate mainly from rural areas, have lower levels of education than other groups and are more obese.

However, Sri Lankans, despite being younger, their short stay in Norway, higher education, low parity and lower BMI show higher WHR for the same BMI, indicating a more complex interplay of these factors. Others have discussed the impact of socio-demographic factors in more detail, both concerning a possible increase in socio-economic gradient with time after migration, and the complexity of using SEP variables across ethnic groups being in different stages of transition in the European pattern of health inequalities.25

Greater proportions of women were found to be overweight and obese compared to men, except for the Vietnamese. Immigrant women26 might be shielded from Western societal norms and their associations with body image could differ in being more comfortable with extra kilograms. However, our data, being cross-sectional and quantitative, limit such inferences and these underlying processes must be pursued.

All immigrant groups were sedentary, notwithstanding the methodological limitations in assessing physical activity correctly in population-based surveys. Validity problems of questionnaire data are greater in immigrants given the language problems, different conceptual content, relevance and cultural norms about leisure time physical activity. However, for immigrants living in a cold northern Western country, outdoor physical activity remains challenging.

Discussing the socio-cultural adaptation, including issues such as integration, is beyond the scope of this study. However, it is clear that the differences between the ethnic groups in their socio-demographic characteristics and their migration history indicate that this adaptation varies by ethnicity. This is also confirmed by comparison with the ethnic Norwegian population, where differences are greatest with Pakistanis and Turks, but not as great with Iranians and Sri Lankans.

In summary, we found large differences in generalized and central obesity between immigrant groups from developing countries that add to the existing public health challenges. Diversity in obesity patterns between and within ethnic groups despite similarities in the physical environment has been documented. However, data constraints limit any inferences to gene–environmental interactions. Pathways between socio-demographic factors associated with obesity, particularly the directional effects of these relationships, need further investigation. The high prevalence of central adiposity in the South Asians identifies an obvious need for a long-term strategy of early prevention, particularly among young women. Minorities are often at cross-roads, and tailor-made strategies that are culturally sensitive need to be designed, developed and evaluated to halt this burgeoning epidemic.

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Acknowledgements

We thank Kathleen Glenday and Zumin Shi for assistance, Anne Johanne Søgaard and Aage Tverdal for valuable comments. The data collection was conducted as part of the Oslo Immigrant Health Study 2002 in collaboration with the Norwegian Institute of Public Health. BNK, HM, GHO and MW contributed to the conception and design of the study. BNK, HM and ID analysed the data and all authors contributed to the interpretation of the data. BNK drafted the article and HW, MW, GHO and ID commented upon and revised the drafts. All authors gave their approval to the final version submitted for publication. The Oslo Immigrant Health Study was funded by the Norwegian Institute of Public Health and University of Oslo. BNK's doctoral grant was funded through the Norwegian Research Council, and the Norwegian Directorate for Health and Social Affairs, Nutrition Division financially supported this piece of work. Competing interests: None declared.

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Kumar, B., Meyer, H., Wandel, M. et al. Ethnic differences in obesity among immigrants from developing countries, in Oslo, Norway. Int J Obes 30, 684–690 (2006). https://doi.org/10.1038/sj.ijo.0803051

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Keywords

  • ethnic minorities
  • immigrants
  • body mass index
  • waist circumference
  • waist hip ratio

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