Heterogeneity of coronary heart disease risk factors in Indian, Pakistani, Bangladeshi, and European origin populations: cross sectional studyBMJ 1999; 319 doi: http://dx.doi.org/10.1136/bmj.319.7204.215 (Published 24 July 1999) Cite this as: BMJ 1999;319:215
- Raj Bhopal, professor ()a,
- Nigel Unwin, senior lecturer in epidemiologyb,
- Martin White, senior lecturer in public health medicinea,
- Julie Yallop, research associateb,
- Louise Walker, research associateb,
- K G M M Alberti, professorc,
- Jane Harland, research associateb,
- Sheila Patel, research associateb,
- Naseer Ahmad, research associateb,
- Catherine Turner, research nurseb,
- Bill Watson, research associateb,
- Dalvir Kaur, study administratorb,
- Anna Kulkarni, research nurseb,
- Mike Laker, readerd,
- Anna Tavridou, PhD studentd
- a Department of Epidemiology and Public Health, Medical School, University of Newcastle, Newcastle upon Tyne NE2 4HH
- b Departments of Medicine and Epidemiology and Public Health, Wellcome Laboratories, Royal Victoria Infirmary, Newcastle upon Tyne
- c Department of Medicine, Medical School, University of Newcastle
- d Department of Clinical Biochemistry, Medical School, University of Newcastle
- Correspondence to: R Bhopal Public Health Sciences, Medical School, Edinburgh EH8 9AG
- Accepted 28 April 1999
Objective: To compare coronary risk factors and disease prevalence among Indians, Pakistanis, and Bangladeshis, and in all South Asians (these three groups together) with Europeans.
Design: Cross sectional survey.
Setting: Newcastle upon Tyne.
Participants: 259 Indian, 305 Pakistani, 120 Bangladeshi, and 825 European men and women aged 25-74 years.
Main outcome measures: Social and economic circumstances, lifestyle, self reported symptoms and diseases, blood pressure, electrocardiogram, and anthropometric, haematological, and biochemical measurements.
Results: There were differences in social and economic circumstances, lifestyles, anthropometric measures and disease both between Indians, Pakistanis, and Bangladeshis and between all South Asians and Europeans. Bangladeshis and Pakistanis were the poorest groups. For most risk factors, the Bangladeshis (particularly men) fared the worst: smoking was most common (57%) in that group, and Bangladeshis had the highest concentrations of triglycerides (2.04 mmol/l) and fasting blood glucose (6.6 mmol/l) and the lowest concentration of high density lipoprotein cholesterol (0.97 mmol/l). Blood pressure, however, was lowest in Bangladeshis. Bangladeshis were the shortest (men 164 cm tall v 170 cm for Indians and 174 cm for Europeans). A higher proportion of Pakistani and Bangladeshi men had diabetes (22.4% and 26.6% respectively) than Indians (15.2%). Comparisons of all South Asians with Europeans hid some important differences, but South Asians were still disadvantaged in a wide range of risk factors Findings in women were similar.
Conclusion: Risk of coronary heart disease is not uniform among South Asians, and there are important differences between Indians, Pakistanis, and Bangladeshis for many coronary risk factors. The belief that, except for insulin resistance, South Asians have lower levels of coronary risk factors than Europeans is incorrect, and may have arisen from combining ethnic subgroups and examining a narrow range of factors.
South Asians have more coronary heart disease than Europeans despite apparently lower levels of risk factors
This study shows that Indians, Pakistanis and Bangladeshis differ in a wide range of coronary risk factors and combining their data is misleading
Among South Asians, Indians were least and Bangladeshis most disadvantaged in a range of coronary risk factors. South Asians were disadvantaged in comparison with Europeans
Future research and prevention strategies for coronary heart disease in South Asians should acknowledge a broad range of risk factors, the heterogeneity of these populations, linguistic and cultural needs, and environmental factors
Coronary heart disease is apparently commoner in South Asians in Britain than in the general population1 despite lower levels of several classic coronary risk factors.2 3 Insulin resistance is proposed to be the underlying factor in high rates of coronary heart disease among South Asians worldwide and has been related to lack of exercise and obesity. Bhopal, and Shaukat and de Bono, however, emphasised a wide range of risk factors including smoking and poverty.4 5 Williams et al concluded that South Asians had a higher prevalence of a broad range of non-biochemical risk factors than the general population.6 Nazroo showed that the prevalence of self reported coronary heart disease was higher in Bangladeshis and Pakistanis combined, and lower in Indians, than in the white population after standard of living was adjusted for.7 The Newcastle heart project compared coronary heart disease risk factors in Indians, Pakistanis, and Bangladeshis and also compared South Asians as a whole with Europeans.8 9
Participants and methods
The methods and some data on the European study have been published,8 9 and more detail is available on the BMJ's website. South Asians are defined as Newcastle residents with ancestral origins in India, Pakistan, or Bangladesh and who had three or more grandparents born there. Indians, Pakistanis, and Bangladeshis self identified as such at interview, using 1991 census categories of ethnic group Europeans are defined as Newcastle residents with ancestral origins in European countries and were identified by excluding people from ethnic minority populations. In referring to published work we generally use the authors' terms (white, general population, etc).
We selected European subjects from the 6448 people identified from the family health services authority register for the Newcastle health and lifestyle survey (NHLS).8 9 People with South Asian sounding names were selected from the full register.10 The age group studied was 25-74 years. The sampling frame was divided into 10 year age and sex strata, and equal numbers from each stratum randomly selected. Europeans were screened between April 1993 and October 1994 and South Asians between May 1995 and March 1997.
Participants not requiring insulin fasted from 2200 the night before attending a clinic at Royal Victoria Infirmary, Newcastle. Venous blood was taken for the measurement of lipids (including Lp(a) lipoprotein), insulin, and glucose. Subjects not reporting a diagnosis of diabetes took a standard World Health Organisation oral glucose tolerance test and glucose tolerance was based on the 2 hour result, as previously described.9 Insulin was measured using an enzyme linked immunosorbent assay (DAKO Diagnostics, Ely).
Anthropometric measurements, blood pressure, pulse, and electrocardiography
Height, weight, waist and hip circumference, and blood pressure were measured as previously described for the European subjects.8 9 We used established criteria to define risk factors for coronary heart disease.11 12 Participants with a carbon monoxide concentration >8 ppm on the Bedfast Smokerlyzer carbon monoxide monitor13 and who did not admit to smoking were counted as carbon monoxide adjusted smokers. A 12 lead resting electrocardiogram was recorded and Minnesota coded by two independent coders.8
Participants completed a questionnaire including questions on state of health, health behaviour, and socioeconomic circumstances. Europeans self completed the questionnaire. The questionnaire was translated into four South Asian languages then independently retranslated into English, with translators and researchers conferring and agreeing on equivalence of meaning. South Asian interviewers completed the questionnaire in the participants' homes and preferred languages. The Rose chest pain questionnaire was interpreted as recommended.14
Analysis of data
We analysed data using SPSS/PC+ version 6. Direct age standardisation was to the 1991 England and Wales population. Differences between Europeans and South Asians for continuous variables were assessed by independent samples t tests, and differences between Indians, Pakistanis and Bangladeshis by analysis of variance. Income data, for men only, were adjusted for household composition using the formula: income/(1+0.7 × adults + 0.5 × children).15 As triglycerides, Lp(a) lipoprotein, and insulin had skewed distributions log transformations were used in analysis and geometric means are presented. For categorical variables, age adjusted variances were calculated.
Newcastle upon Tyne joint ethics committee approved the study. Informed consent was obtained from participants. If participants did not consent to three venepunctures, our priority was baseline and then 2 hour samples. For example, 20 Indian, 26 Pakistani, and 22 Bangladeshi women did not consent to a 2 hour sample.
Of 2160 people with South Asian sounding names, 1050 people were eligible and contacted; 288 refused and 53 completed only the interview, leaving 709 (67.5% of 1050). Of these, 684 classified themselves as Indian, Pakistani, or Bangladeshi Of 1744 people sampled from the Newcastle health and lifestyle survey, 1308 were contacted and 840 were screened (64.2%) Fourteen were South Asian and one of African origin, leaving 825 Europeans.
Table 1 shows Bangladeshi men were the youngest group and the most recent immigrants (data on BMJ's website). Indians were most, and Bangladeshis least, educated. Indians were most likely to be in social classes I, II and IIIN (70%) and Bangladeshis least (26%) Europeans and Indians had the highest median income and Bangladeshis the lowest. Table 2 shows similar findings in women.
Table 3 shows the highest prevalence of smoking was in Bangladeshi men. Pakistanis and Indians were most likely to eat fruit or vegetables daily. Few Pakistanis and Bangladeshis drank alcohol; most Indians did. Indians were the most physically active South Asians, Bangladeshis the least Large differences existed between Europeans and South Asians except in smoking.
Few Indian, Pakistani, or Bangladeshi women smoked or drank alcohol (table 3) Daily consumption of fruit or vegetables was commoner in Indians than in Bangladeshis and Europeans. Bangladeshis were the least, and the Indians themost, physically active South Asians. The differences between Europeans and South Asians were large.
Prevalence of clinical problems
Table 4 shows non-significant variation in diabetes between the three male South Asian groups, which collectively had a five times higher prevalence of diabetes than Europeans. There were important differences between the three South Asian groups in total cholesterol:high density lipoprotein cholesterol ratio and triglyceride concentration. South Asians had lower high density lipoprotein cholesterol concentration, higher total cholesterol: high density lipoprotein cholesterol ratio and higher triglyceride concentrations than Europeans.
Obesity was commoner in Pakistanis and Indians than in Bangladeshis Differences in central obesity between South Asian groups were small Waist: hip ratios of ≥0.95 were commoner in South Asians than Europeans. Differences in hypertension between Indians, Pakistanis and Bangladeshis were not significant, but hypertension was least common in Bangladeshis and less common in South Asians than Europeans.
Prevalence of Rose angina was similar among the South Asian groups and between them and Europeans. Possible myocardial infarction was higher (not significant) in Bangladeshis than Indians or Pakistanis. Evidence of coronary heart disease on electrocardiography was similar among the three South Asian groups, which combined had more probable heart disease than Europeans.
A higher propertion of Indian women had diabetes than Pakistanis and Bangladeshis (not significant). Diabetes was four to five times commoner in South Asians than in Europeans (table 5). Among South Asians, Bangladeshis were most likely to have low high density lipoprotein cholesterol concentration, high cholesterol:high density lipoprotein cholesterol ratio and high triglyceride concentrations. South Asians had a less favourable lipid profile than Europeans with the exception of total cholesterol.
Obesity was commoner in Indian and Pakistani women than in Bangladeshis High waist:hip ratios were commoner in Pakistanis and Bangladeshis, and about four times commoner in South Asians than Europeans.
Coronary heart disease was too rare for reliable comparisons among South Asian groups, but on both questionnaire and electrocardiography there was slightly less coronary heart disease in Bangladeshis than Indians and Pakistanis. South Asians had more possible myocardial infarction on questionnaire and probable coronary heart disease on electrocardiography than Europeans.
Table 6 shows that Bangladeshi men and women had the highest risk profiles for 9 of 15 coronary heart disease risk factors. Indians were advantaged by comparison. South Asians had higher levels than Europeans in 10 of 15 factors.
Newcastle South Asians, mostly from the north of the Indian subcontinent and Sylhet, have a mix of religions, languages, and lifestyles, similar to those described nationally.16 Our findings that coronary risk factors patterns are different in Indians, Pakistanis, and Bangladeshis and that South Asians combined have higher levels than Europeans, probably apply elsewhere. The heterogeneity of South Asian populations has too rarely been acknowledged in the context of coronary heart disease.2 3 17–20 New and larger studies are needed to assess whether the incidence and prevalence of coronary heart disease and diabetes differs between Indians, Pakistanis, and Bangladeshis as suggested here and elsewhere.1 7
We acknowledge potential bias because Europeans self completed the questionnaire whereas South Asians had home interviews and Europeans and South Asians were studied sequentially. These decisions were pragmatic and resource driven; self completion of questionnaires by South Asians was inappropriate, and interviewing Europeans beyond our resources. The South Asian study needed staff with appropriate languages and cultural knowledge so screening them separately was more practical. Changes in disease and risk factors would be small between 1993-4 (European study, midpoint January 1994) and 1995-7 (South Asian study, midpoint August 1996). This paper, moreover, focuses on variations among South Asian subgroups, for whom data were collected simultaneously.
Hypotheses for the high rates of coronary heart disease in South Asians include the use of ghee and other cooking oils21; non-vegetarian diets22; subclinical hypothyroidism23; stress, racism, and poverty6; deprivation in infancy and childhood6 24; and insulin resistance.2 17 The insulin resistance hypothesis has overshadowed other explanations.3 17 25 This study draws attention to a wide range of risk factors and shows that combining data for South Asians is misleading.
As ethnic and racial differences are almost never demonstrably genetic, social and environmental differences are likely to be crucial. Our observations emphasise poverty (among Pakistanis and Bangladeshis), smoking (among Bangladeshis, Pakistanis, and European men), high blood pressure (among Europeans and Indians), obesity (in all groups), and a lack of exercise (in all groups). Our study supports a role for infant deprivation (South Asians were shorter, an indicator of poorer early life nutrition),24 central obesity and insulin resistance (all South Asians), abstinence from alcohol (especially Pakistanis and Bangladeshis), and chronic inflammation (higher white cell counts in Pakistani and Bangladeshi men; data shown on BMJ's website) as potentially important causes of coronary heart disease.26
Strategies to control coronary heart disease in South Asians should emphasise all important factors including social and environmental ones such as employment and poverty, propose linguistic and cultural adaptations, and consider the heterogeneity of Indians, Pakistanis, and Bangladeshis.
We thank Margaret Miller, Mavis Brown, Amanda McEwan, Heather Armstrong, Afroz Qureshi, Ayesha Motala, Kaushik Ramaiya, and Dilip Singh for help at the screening sessions; Peter Stevenson for both screening and analysis of electrocardiograms; Nan Keen for coding electrocardiograms; Denise Howel for statistical advice; David Whiting for writing the name search programme; Linda Ashworth for measuring insulin; Sheinaz Mughal for advice; and Carole Frazer for preparing the manuscript. The interviews were done by a team of 20 interviewers, whom we thank. They were Jusna Ahmed, Mushtaq Ahmed, Shuhel Ahmed, Rafiqul Alam, Masooma Ali, Showkat Ali, Santokh Bamrah, Parul Begum, Manju Chandra, Malik Chaudhry, Shubh Ghai, Amarjit Ghura, Sultana Kimti, Raminder Pal Singh, Rajindar Ghura, Salma Hasan, Nasir Iqbal, Surbhi Khanna, Pardeep Lally, Rakesh Prasad, Arati Roy, Nasim Shafiq, Baldev Singh, Salah Uddin, Anita Sarkar, and Prehlad Kanwar.
Contributors: RB contributed to the study hypotheses and design, supervision of project, planning and interpretation of data analyses, and was the lead writer. NU and MW contributed to the study hypotheses and design, supervision, screening, planning, and interpretation of data. JY participated in management of screening in South Asian study, analysi of data, and drafting methods section. LW participated in preparation and analysis of data, and drafting methods, results, and tables of manuscript. KGMMA contributed to the study hypotheses and design and supervision of project. JH participated in development of study design, methods, and questionnaire for European study, management and screening of European population, and data coding. SP participated in screening South Asians, community liaison and recruitment to study, and data coding. NA contributed to development of South Asian questionnaire, translation, sampling, screening, recruitment, and data preparation.NU, MW, JY, LW, KGMMA, JH, SP, and NA commented on the manuscript CT participated in screening, development of questionnaire, recruitment, and community liaison. BW managed and participated in screening for European and South Asian samples and helped with entry and preparation of data for analysis DK participated in coordination of recruitment and data collection for the South Asian study, data analysis on response rates, and drafting text. AK participated in screening, development of questionnaire, community liaison, and recruitment ML advised on biochemical methods, supervised laboratories doing biochemical tests, and had responsibility for Lp(a) lipoprotein assays. AT participated in the Lp(a) lipoprotein study and provided data and advice on Lp(a) lipoprotein RB, GA, NU, and MW are the study guarantors.
Funding Barclay Trust, British Diabetic Association, Newcastle Health Authority, research and development directorate of the Northern Regional Health Authority, Department of Health, and British Heart Foundation.
Competing interests None declared.
website extra A longer version of this paper is available on the BMJ's website www.bmj.com