Heterogeneity in Blood Pressure in UK Bangladeshi, Indian and

Pakistani, compared to White, populations: divergence of adults

and children

Hartesh S BATTU, Raj BHOPAL, Charles AGYEMANG

THE UNIVERSITY OF EDINBURGH, THE UNIVERSITY OF EDINBURGH and

UNIVERSITY OF AMSTERDAM

Email correspondence to Hartesh Battu: hartesh.battu@doctors.org.uk

[Word Count including references but not tables and legends: (3386 excluding references)]

Number of tables: 1

Number of figures: 5

Supplementary digital content: 3 documents

Running Title: Blood pressure in UK South Asians

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Abstract

Blood pressure (BP) and hypertension prevalence differences between UK South Asians

(Bangladeshis, Indians and Pakistanis) and White Europeans exist in childhood and

adulthood. This meta-analysis sought to quantify these differences. We searched MEDLINE

(1946-2017), EMBASE (1974-2017), and GLOBAL HEALTH (1973-2017) for comparative

studies and pooled the data with Revman (Cochrane Collaboration). Twenty-two studies were

included - fourteen on adults and eight on children. South Asian adults had lower systolic and

slightly lower diastolic BP. However, stark heterogeneity existed between South Asian

subgroups: Bangladeshis had markedly lower systolic BP (mean difference: -11.7mmHg in

men and women); Indians slightly lower (-2.0mmHg in men and -4.5mmHg in women); and

Pakistanis intermediately lower (-7.9mmHg in men and -8.6mmHg in women), compared to

White Europeans. However, South Asian children did not have lower systolic or diastolic BP

compared to White children, and their BP was often higher. This intergenerational change in

BP difference mirrored the change in body mass index (BMI) difference, particularly in

Bangladeshis. We conclude that ethnicity-related BP differences are heterogeneous and

dependent on age, sex and South Asian subgroup. South Asian children do not have lower BP

than White Europeans in contrast to their adult counterparts. There is concern that this pattern

may continue into adulthood, worsening the already high cardiovascular disease burden in

South Asians in future years. Further research is needed to ascertain the causes of this

evolving issue.

[Word Count: 229 / 250]

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Introduction

UK South Asians (Bangladeshis, Indians and Pakistanis) have higher incidence and mortality

from stroke, angina and myocardial infarction than White European populations (1, 2).

Biological, sociocultural, environmental and genetic hypotheses have been advanced to help

explain these differences (1). The role of hypertension, recognised as the leading risk factor

in global mortality (3, 4), has been explored in previous epidemiological studies and

systematic reviews examining blood pressure (BP) differences in South Asian groups (5-7).

In these reviews, South Asian adults had lower systolic blood pressure (SBP) but similar

diastolic blood pressure (DBP) overall compared to White Europeans, with important

differences identified between South Asian subgroups; specifically, slightly higher BP in

Indians, slightly lower in Pakistanis and much lower in Bangladeshis (5). A concerning

finding has been that South Asian children have higher BP than their White counterparts (6),

a difference which may track into adulthood and increase cardiovascular disease risk.

Despite these systematic reviews, there are still conflicting views about how BP differs

between South Asians and White Europeans in the academic and patient-oriented literature

(8, 9). Some writers claim that blood pressure is higher in South Asian populations than in

White European ones. Other than a recent meta-analysis (7) identifying that BP is lower in

South Asians originating from countries where Islam is the dominant religion, there is still

little emphasis on heterogeneity in different South Asian groups. Given the importance of

blood pressure, clarity and consensus is needed on this matter. This paper reviews the nature

of these BP differences. It updates previous reviews (5, 6) by including critically important

datasets published more recently, such as the Health Surveys for England (HSE) 2004 (10,

11) and the Child Heart and Health Study in England (CHASE) (12). It also presents data by

heterogeneous South Asian subgroups and presents the results of meta-analyses as Forest

plots to quantify the differences and aid interpretation. Children’s and adults’ data are

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presented to focus on inter-generational differences which help to predict cardiovascular risk

in South Asians in the future.

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Methods

Search Strategy

PRISMA guidelines were followed. EMBASE (1974 - 2017), MEDLINE (1946 - 2017) and

GLOBAL HEALTH (1973 - 2017) were searched by combining Medical Subject Headings

(MeSH) and keywords related to BP and South Asian ethnicity. Box 1 shows the detailed

strategy.

1. blood pressure/

2. blood pressure*.ti,ab

3. hypertension.ti,ab

4. 1 OR 2 OR 3

5. Asian continental ancestry group/

6. (Asian* OR Indian* OR Pakistani* OR Bangladeshi* OR Sri Lankan*).ti,ab

7. 5 OR 6

8. 4 AND 7

Box 1 – Search strategy

Searching across the databases was completed by HB on 02/10/17. Duplicates were

subsequently removed. Titles and abstracts were read to select potentially relevant papers on

UK participants. Inclusion and exclusion criteria were applied using full texts of the

remaining studies.

References of studies were examined for relevant studies. Additional papers were identified

using the “cited by” functions on PubMed and Google Scholar. Studies known to RB and CA

were included eg the reports of the Health Surveys for England (HSE) 1999 (13, 14) and

2004 (10, 11).

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Inclusion and Exclusion Criteria

Included studies measured BP in population-based samples of UK South Asian populations in

comparison with UK White European populations. Analysis was restricted to the UK as this

allowed us to compare blood pressure against a single reference population. Additionally, we

were aware that the majority of studies in this field were conducted in the UK setting.

The exclusion criteria were:

Reviews, meta-analyses, conference proceedings, case reports and letters.

Studies of either South Asian or White European populations only.

Studies of clinically-selected samples.

Studies not written in English.

Data Extraction

Study characteristics, population demographics and BP data (mmHg) were extracted by HB.

Where available, hypertension rates, anti-hypertensive medication usage rates and Body Mass

Index (BMI; kg/m2) data were extracted, alongside P-values and standard deviations. To

ensure accuracy, extracted data were verified by CA.

Data Analysis

Studies were grouped by ethnic group (eg Bangladeshi compared with White or Indian

compared with White). Mean BP, standard deviations and sample sizes were entered into

RevMan 5.3 (Cochrane Collaboration, Denmark) to calculate mean differences with 95%

confidence intervals, and to produce Forest plots with summary estimates using random

effects models. Where standard deviations were not reported, standard errors were entered

into the RevMan calculator to obtain them. This was also done for mean BMI, where

reported, and presented alongside the mean BP plots. Studies that reported only on combined

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sex groups or South Asians homogenously were not meta-analysed because of previously

highlighted and potentially misleading heterogeneity.

To assess their validity, included studies were assessed using subjective measures addressing

sampling, method of BP measurement and whether anti-hypertensive medication usage was

considered. For each criterion, a rating was assigned. The results are located in

[supplementary digital content].

Ethnicity – Concepts and Terms

We used recognised and standard concepts, terms and approaches. In the UK the concept of

ethnicity is used rather than race. Ethnicity is based on group identity and is mostly self-

selected from a list of ethnic groups based on the approach of the UK censuses. By South

Asian we include migrants from the countries of South Asia and their descendants living in

the UK. These groups are mainly self-defined Indian, Pakistani and Bangladeshi. The

comparison was with any White European population, or the general population which is

predominantly White European in the UK. Following the UK censuses we capitalise ethnic

group terms (though whenever appropriate we use the approach of the original authors) (15).

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Results

Search and Study Characteristics

Fig.1 shows the search flow diagram. Twenty-two studies (1-22) were included – fourteen on

adults (1-14) and eight on children and infants (15-22). References are presented in box 2.

Data were on 13 581 South Asians (8 988 adults and 4 593 children) and 105 659 White

Europeans (87 368 adults and 18 017 children). Since the previous reviews, two additional

studies (2, 14) in adults and five (17-22) in children were identified. No studies involved Sri

Lankans.

Table 1 shows the wide variation in study characteristics. Twenty-one (1-19, 21, 22) had a

cross-sectional design while one (20) was prospective longitudinal. Twenty (1-7, 9-16, 18-22)

were in England, one (17) in England and Wales and one (8) in Glasgow, Scotland. Samples

were derived from electoral registers and/or postcode sectors (8, 13, 14, 16, 18), general

practice lists (2-5), schools (15, 17, 19, 21, 22), workplaces (1, 7, 11), or local health

authority registers (10). One (6) sampled a combination of workplaces and general practice

lists and one (20) a hospital. Only twelve (3, 6, 8-10, 12-14, 16-18, 22) studies specified the

time-period in which data collection occurred.

In all studies (1-22), the aim involved comparing ethnicities. Thirteen (3-12, 15, 17) aimed to

investigate various cardiovascular risks, five (1, 2, 19, 20, 22) had BP-specific aims, while

four (13, 14, 16, 18) were part of the Health Surveys for England.

Assignment and indicators of ethnicity varied widely. Nine studies (5-10, 17, 19, 22)

employed multiple measures, including appearance (6, 17), country of birth (5, 6), parental

origin (9, 17, 19), grandparental origin (5, 10, 19), name (5-10) and self-reported ethnicity (7,

10). Others relied on self/parent-reported ethnicity (4, 12-14, 16, 18, 21), appearance (15) or

grandparental origin (20). Four (1-3, 11) studies did not specify how ethnicity was assigned.

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Table 1 shows the wide variety of response rates and age-groups studied. Of note are the

significantly lower response rates amongst Bangladeshis (2, 3, 13, 14, 16, 18). The Health

Surveys for England (13, 14, 16, 18) reported measurements for 5-15, 16-34, 35-54 and >55

year-olds, providing rich data on age-related BP patterns. Tables 2-6 show that some (3, 5, 7-

12, 17) studies provided adjusted BP; some (1, 2, 4, 13-16, 18-22) provided raw means and

one (6) provided a median.

Blood Pressure and BMI

Bangladeshi compared with White Ethnic Groups

Seven studies compared Bangladeshi with White populations: four in adults and three in

children (fig.2). BP, BMI and hypertension data are available in tables 1-3 in supplementary

document 3.

Bangladeshi men had lower mean SBP, DBP and BMI than White men (fig.2a shows pooled

mean differences of -11.72mmHg, -4.71mmHg and -2.23kg/m2, respectively). Bangladeshi

boys had higher mean SBP and DBP, but lower BMI than White boys across three studies

(fig.2b; mean differences of 0.37mmHg, 1.98mmHg and -0.32kg/m2, respectively). However,

only the difference in DBP had 95% CIs which excluded zero.

Mean SBP and DBP were lower in Bangladeshi women (fig.2c shows pooled mean

differences of -11.68mmHg and -2.34mmHg respectively) while BMI was lower in three

studies (mean difference of -1.32kg/m2). In three studies, Bangladeshi girls had lower mean

SBP, higher DBP and lower BMI (fig.2d; pooled mean differences of -1.49mmHg,

1.72mmHg and -0.22kg/m2, respectively). The 95% CIs for the difference in SBP excluded

zero while for DBP and BMI both 95% CIs included zero.

Indian compared with White Ethnic Groups

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Nine studies compared Indian with White populations; five in adults and four in children

(fig.3). BP, BMI and hypertension data are available in tables 4-6 in supplementary document

3.

In three out of five studies, Indian men had lower mean SBP than White men. Figure 3a

shows a pooled mean difference of -1.95mmHg, but the 95% CI included zero. Mean DBP

was higher in Indian men in three studies, equal in one and lower in one (fig.3a shows a

pooled mean difference of -0.32mmHg). Mean BMI was lower in Indian men in four studies

(fig.3a; pooled mean difference: -0.9kg/m2), with 95% CIs excluding zero. Indian boys had

higher mean SBP in two of four studies (fig.3b; pooled mean difference of 0.35mmHg) and

higher mean DBP in four studies (fig.3b; pooled mean difference of 2.04mmHg), but only the

DBP difference had 95% CIs that excluded zero. Their mean difference in BMI was -

0.21kg/m2 (fig.3b).

In three out of four studies, Indian women had lower mean SBP and DBP than White women

(fig.3c shows pooled mean differences of -4.46mmHg and -1.19mmHg, respectively). Mean

BMI was lower in two studies and higher in two studies (fig.3c; pooled mean difference:

0.21mmHg). Only the SBP difference had a 95% CI excluding zero. In two out of four

studies, Indian girls had higher mean SBP (fig.3d; pooled mean difference: 0.37mmHg).

Mean DBP was higher in all four studies (fig.3d; pooled mean difference: 1.14mmHg). There

was little difference (-0.08kg/m2) in mean BMI.

Pakistani compared with White Ethnic Groups

Six studies compared Pakistani with White populations; three in adults and three in children

(fig.4). BP, BMI and hypertension data are available in tables 7-9 in supplementary document

3.

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Pakistani men had lower mean SBP and DBP than White men (fig.4a shows pooled mean

differences of -7.87mmHg and -3.8mmHg, respectively). Mean BMI was lower in two out of

three studies, with the 95% CI for the pooled value excluding zero (fig.4a; pooled mean

difference: -0.67kg/m2). In two studies, Pakistani boys had higher mean SBP and in all three

studies higher DBP (fig.4b; pooled mean difference: 1.28mmHg and 2.76mmHg,

respectively). There was no difference in mean BMI.

Pakistani women had lower mean SBP than White women, lower DBP in two studies and

higher BMI in three studies (fig.4c shows pooled mean differences of -8.56mmHg, -

1.52mmHg and 0.63kg/m2, respectively). The SBP difference had 95% CIs excluding zero.

Pakistani girls had lower mean SBP in two studies, higher mean DBP in two studies and

lower BMI in two studies (fig.4d; mean differences: -0.49mmHg, 0.75mmHg and -0.2kg/m2,

respectively). None of the 95% CIs excluded zero.

Age and Inter-Ethnic Blood Pressure Variation

Fig.5 shows blood pressure differences between South Asian groups and White populations

stratified by age using cross-sectional data from the Health Surveys for England 1999 and

2004 shown separately. The data are available in tables 1, 4 and 7 in supplementary

document 3.

In Bangladeshi males the comparatively lower BP is not seen in the younger age groups (figs

5a and 5d). In Indian males the SBP was similar at all ages in 1999 but lower at all but the

youngest group in 2004 (fig 5b). The DBP was higher at most ages in Indians (fig 5e). In

Pakistani males SBP was variable but not lower in the youngest group (fig 5c). DBP was

higher in younger Pakistani males and similar in older groups (fig 5f).

In Bangladeshi females the patterns for SBP and DBP were U-shaped, but no data were

available for >55s (figs 5g and 5j). In Indian females the SBP and DBP was consistently

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slightly higher in most age groups (figs 5h and 5k). In Pakistani females, there was a U-

shaped curve with SBP and DBP being higher in the oldest group and similar or slightly

higher in the youngest group (figs 5i and 5l).

Box 2 – Included Studies1. Cruickshank JK, Jackson SH, Bannan LT, Beevers DG, Beevers M, Osbourne VL. Blood pressure in black, white and Asian factory workers in Birmingham. Postgraduate Medical Journal. 1983;59(696):622.2. Silman AJ, Evans SJ, Loysen E. Blood pressure and migration: a study of Bengali immigrants in East London. Journal of epidemiology and community health. 1987;41(2):152-5.3. McKeigue PM, Marmot MG, Syndercombe Court YD, Cottier DE, Rahman S, Riemersma RA. Diabetes, hyperinsulinaemia, and coronary risk factors in Bangladeshis in east London. British heart journal. 1988;60(5):390-6.4. Miller GJ, Kotecha S, Wilkinson WH, Wilkes H, Stirling Y, Sanders TA, et al. Dietary and other characteristics relevant for coronary heart disease in men of Indian, West Indian and European descent in London. Atherosclerosis. 1988;70(1-2):63-72.5. Cruickshank JK, Cooper J, Burnett M, MacDuff J, Drubra U. Ethnic differences in fasting plasma C-peptide and insulin in relation to glucose tolerance and blood pressure. Lancet (London, England). 1991;338(8771):842-7.6. McKeigue PM, Shah B, Marmot MG. Relation of central obesity and insulin resistance with high diabetes prevalence and cardiovascular risk in South Asians. Lancet (London, England). 1991;337(8738):382-6.7. Knight TM, Smith Z, Whittles A, Sahota P, Lockton JA, Hogg G, et al. Insulin resistance, diabetes, and risk markers for ischaemic heart disease in Asian men and non-Asian in Bradford. British heart journal. 1992;67(5):343-50.8. Williams R, Bhopal R, Hunt K. Health of a Punjabi ethnic minority in Glasgow: a comparison with the general population. Journal of epidemiology and community health. 1993;47(2):96.9. Cappuccio FP, Cook DG, Atkinson RW, Strazzullo P. Prevalence, detection, and management of cardiovascular risk factors in different ethnic groups in south London. Heart. 1997;78(6):555-63.10. Bhopal R, Unwin N, White M, Yallop J, Walker L, Alberti KGMM, et al. Heterogeneity of coronary heart disease risk factors in Indian, Pakistani, Bangladeshi, and European origin populations: cross sectional study. BMJ. 1999;319(7204):215.11. Whitty CJ, Brunner EJ, Shipley MJ, Hemingway H, Marmot MG. Differences in biological risk factors for cardiovascular disease between three ethnic groups in the Whitehall II study. Atherosclerosis. 1999;142(2):279-86.12. Primatesta P, Bost L, Poulter NR. Blood pressure levels and hypertension status among ethnic groups in England. Journal of human hypertension. 2000;14(2):143-8.13. Karlsen S, Primatesta P, McMunn A. Blood Pressure (Chapter 7). In: Erens B, Primatesta P, Prior G, editors. Health Survey for England - The Health of Minority Ethnic Groups '99. London: The Stationery Office; 2001. p. 175-97.14. Chaudhury M, Zaninotto P. Blood Pressure (Chapter 7). In: Sproston K, Mindell J, editors. Health SUrvey for England - The Health of Minority Ethnic Groups '04. London: The Stationery Office; 2006. p. 205-36.15. De Giovanni JV, Pentecost BL, Beevers DG, Beevers M, Jackson SH, Bannan LT,

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et al. The Birmingham blood pressure school study. Postgraduate Medical Journal. 1983;59(696):627-9.16. Nazroo J, Becher H, Kelly Y, McMunn A. Children's Health (Chapter 13). In: Erens B, Primatesta P, Prior G, editors. Health Survey for England — The Health of Minority Ethnic Groups '99. London: The Stationery Office; 2001.17. Whincup PH, Gilg JA, Papacosta O, Seymour C, Miller GJ, Alberti KG, et al. Early evidence of ethnic differences in cardiovascular risk: cross sectional comparison of British South Asian and white children. Bmj. 2002;324(7338):635.18. Fuller E. Children's Health (Chapter 12). In: Sproston K, Mindell J, editors. Health Survey for England - The Health of Minority Ethnic Groups '04. London: The Stationery Office; 2006. p. 377-400.19. Harding S, Maynard M, Cruickshank JK, Gray L. Anthropometry and blood pressure differences in black Caribbean, African, South Asian and white adolescents: the MRC DASH study. Journal of hypertension. 2006;24(8):1507-14.20. Bansal N, Ayoola OO, Gemmell I, Vyas A, Koudsi A, Oldroyd J, et al. Effects of early growth on blood pressure of infants of British European and South Asian origin at one year of age: the Manchester children's growth and vascular health study. Journal of hypertension. 2008;26(3):412-8.21. Henderson EJ, Jones CH, Hornby-Turner YC, Pollard TM. Adiposity and blood pressure in 7- to 11-year-old children: comparison of British Pakistani and white British children, and of British Pakistani children of migrant and British-born mothers. American journal of human biology : the official journal of the Human Biology Council. 2011;23(5):710-6.22. Thomas C, Nightingale CM, Donin AS, Rudnicka AR, Owen CG, Cook DG, et al. Ethnic and socioeconomic influences on childhood blood pressure: the Child Heart and Health Study in England. Journal of hypertension. 2012;30(11):2090-7.

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Discussion

Key Findings

The clear heterogeneity in BP in UK adult South Asian subgroups, with lower BP compared

with White populations, is absent in South Asian children. Pakistani and Bangladeshi adults

especially had lower SBP and DBP than White European adults, but the children did not;

there was even evidence for higher BP than in White European children. In Indian adults, the

lower SBP in women was not seen in Indian girls. Indian boys had higher DBP than White

European boys. South Asian adults, especially men, tended to have lower BMIs than White

European adults, but South Asian children had similar BMIs to White European children. In

Bangladeshi males and females, this change in BMI in adults and children mirrors the change

in BP. The Health Surveys for England showed a complex pattern across age, but while in

adult groups BP was often lower, especially in 15-55 age groups, this was never the case for

age groups under 16 years.

Strengths and Limitations

This study has several strengths. The broad-ranging search combined with knowledge of the

grey-literature allowed us to identify several large and relevant studies. Comparison of mean

differences (rather than absolute BP values) allowed us to combine data even when different

BP devices were used. Our focus on heterogeneous subgroups granted key insights that

would be lost by combining all South Asians.

The study has limitations. The Health Surveys for England (10, 11, 13, 14) did not report BP

data in some age groups because of small sample sizes. Some studies compared groups which

differed significantly in age profile without age-adjustment. The South Asian groups were

usually younger. Some studies did not use population samples which may bias the results. For

example, studies that used occupational samples (16-19) may suffer from healthy-worker

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effects, where the chronically unwell (who are more likely to have adverse BP) are more

likely to be unemployed (20). Some studies did not report anti-hypertensive usage rates.

Where these were reported, they were generally lower in Bangladeshis and Pakistanis, and

higher in Indians (tables 7-9), corroborating that Bangladeshis and Pakistanis have lower BP

and that Indians have higher BP than measured, compared to White Europeans.

Findings in Relation to the Scientific Literature

Hypertension is the leading modifiable risk factor for cerebrovascular disease (21). In a meta-

analysis of predominantly White European-origin populations (22), a log-linear relationship

between BP and stroke mortality was found: each 20mmHg increase in SBP was associated

with twofold increases in stroke mortality. The prospective randomised controlled SPRINT

trial of 9361 participants found that “intensive” BP control (target SBP of <120mmHg)

resulted in lower all-cause mortality than standard control (target SBP of <140mmHg) at a

median follow-up of 3.26 years (hazard ratio: 0.73; 95% CI 0.6 to 0.9) (23). In their 20-year

prospective longitudinal study of predominantly Sikh Punjabi UK South Asians, Eastwood et

al found that SBP and DBP were even more strongly correlated with stroke risk than in White

Europeans, after adjusting for age, smoking status, blood lipid profile, diabetes mellitus,

physical activity and heart rate (24). The evidence that even mildly elevated BP is deleterious

to stroke and mortality risk - particularly in South Asians - is growing.

With new data and heterogeneous analysis of Bangladeshis, Indians and Pakistanis, this

review supports previous findings (5, 7) that BP is lower in UK Bangladeshi and Pakistani

adults, but that BP in Indian and White European adults is similar. In addition, it strengthens

the finding that this lower BP is not mirrored in Bangladeshi and Pakistani children (6), and

that BMI may play a role in this, particularly in Bangladeshis.

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Despite having lower BP, UK Bangladeshi adults have been shown to have markedly higher

mortality from cerebrovascular (approximately 2-2.5 fold) and all circulatory (approximately

1.5-fold) disease compared to their White counterparts (2). This paradox has been highlighted

previously (25, 26). Higher stroke mortality is also evident amongst UK Indians and

Pakistanis (2). Numerous explanatory factors have been proposed. Smoking is known to be

more prevalent amongst Bangladeshi men than White Europeans, Indians and Pakistanis (27).

Lipid profiles amongst South Asians generally are adverse, with tendencies towards elevated

triglycerides and lower high-density lipoprotein (HDL), although total cholesterol is usually

lower (28-30). South Asians exercise less (31) and Bangladeshis in particular are known to be

of lower socioeconomic status than White Europeans (31). Recently, attention has shifted to

the hypothesis that hyperglycaemia may be a factor in excess cardiovascular disease risk in

South Asians (32), and there have been calls for non-classical potential risk factors such as

squatting at stool (linked to central arterial pressure), vitamin D deficiency, infection and

tobacco chewing to be investigated (25).

This review’s finding that Bangladeshi and Pakistani children do not have lower BP than

White Europeans is concerning as it may signal the loss of a major protective factor against

stroke in later life if it tracks into adulthood. Evidence suggests that this might occur. In their

meta-analysis of 50 studies, Chen et al (33) reported the childhood to adulthood BP tracking

mean correlation coefficients as 0.38 for SBP and 0.28 for DBP. However, most studies

included in the analysis were done on European or US populations. We are

unaware of any BP tracking cohort studies performed on South Asians, but the United States

Bogalusa Heart Study (34) compared Black and White populations over 15-year follow-ups.

It found that BP tracking was similar in both groups, ranging from 0.36 to 0.49 in the White

group and 0.38 to 0.50 in the Black group in SBP, and 0.26 to 0.42 in the White group and

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0.19 and 0.41 in the Black group in DBP. Research is needed to determine whether such an

association exists in South Asians.

Combining the evidence that even mildly elevated BP increases stroke risk; that elevated BP

is even more strongly correlated with stroke in South Asians than in White Europeans; that

Bangladeshi and Pakistani children do not have the BP-protection as seen in their adult

counterparts, which may track into adulthood; and that Bangladeshi and Pakistani children

are more likely to engage in poor dietary and physical inactivity behaviours than White

children (1), there is concern that the cardiovascular disease epidemic amongst Bangladeshis

and Pakistanis may worsen in the future, particularly when this current generation of children

reach old-age.

We identified, most clearly in Bangladeshis, that the change in difference in BP from adults

to children was mirrored by the change in difference in BMI. In adults, it is recognised that

BP is linearly correlated with BMI, and that hypertension is associated with obesity (35-37).

These associations have also been identified in Chinese pre-school children, where a 1kg/m2

difference in BMI was positively correlated with 1.2mmHg mean differences in SBP and

DBP in non-obese children (38). In Ethiopian, Vietnamese and Indonesian adult populations,

the BMI - BP correlation coefficient ranged between 0.23 and 0.27 in a cross-sectional study

(39). The evidence suggests that higher BMI causes higher BP in adults and children of

various ethnicities. Therefore, the finding that Bangladeshi children no longer have lower BP

than White Europeans may be partly explained by them no longer having lower BMI.

Conclusion

The confusion over whether BP is higher or lower in UK South Asians is caused by complex

heterogeneity: we have shown that it depends on ethnic subgroup (Bangladeshi, Indian or

Pakistani), sex and age. The pattern of lower BP in UK Bangladeshi and Pakistani adults in

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comparison to White Europeans is not evident in Bangladeshi and Pakistani children. This

pattern of change was seen clearly in both BP and BMI in Bangladeshis. Given the linear

relationship between BP and stroke, and that South Asians already have a significantly higher

risk of stroke and coronary artery disease than White Europeans, these findings are

concerning as they suggest that the stroke and coronary artery disease burden may increase

further still amongst South Asians and particularly Bangladeshis.

No funding

Conflicts of interest: The authors declare no conflict of interest.

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Figure Legends

Figure 1 - Search flow diagram. See supplementary document 1 for details of 42 excluded

studies.

Figure 2a - Blood pressure and BMI in Bangladeshi compared with White European men

Figure 2b - Blood pressure and BMI in Bangladeshi compared with White European boys

Figure 2c - Blood pressure and BMI in Bangladeshi compared with White European women

Figure 2d - Blood pressure and BMI in Bangladeshi compared with White European girls

Figure 3a - Blood pressure and BMI in Indian compared with White European men

Figure 3b - Blood pressure and BMI in Indian compared with White European boys

Figure 3c - Blood pressure and BMI in Indian compared with White European women

Figure 3d - Blood pressure and BMI in Indian compared with White European girls

Figure 4a - Blood pressure and BMI in Pakistani compared with White European men

Figure 4b - Blood pressure and BMI in Pakistani compared with White European boys

Figure 4c - Blood pressure and BMI in Pakistani compared with White European women

Figure 4d - Blood pressure and BMI in Pakistani compared with White European girls

Figure 5 – Age-related BP differences using data from the Health Surveys for England 1999

(“1999”) and 2004 (“2004”). Note that data are cross-sectional; not longitudinal.

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