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7 Blood pressure
Saffron Karlsen, Paola Primatesta and Anne McMunn SUMMARY
The relationship between coronary heart disease (CHD) and stroke and raised systolic and diastolic blood pressure has been well established.1,2,3 A meta-analysis of clinical trials of high blood pressure management has indicated that a reduction of 5-6 mmHg in diastolic blood pressure (DBP) was associated with a highly significant reduction in morbidity and mortality from cardiovascular disease in 36,908 patients with high blood pressure from 14 randomised trials in Europe, the United States and Australia.4 The control of high blood pressure is an important factor in reducing the morbidity and mortality associated with cardiovascular disease. Differences in the prevalence of raised blood pressure among different minority ethnic groups have been found across the world and in different areas in England. Some,5,6 but not all these studies,7 showed higher rates of raised blood pressure among some minority ethnic groups, particularly among people of Black Caribbean and South Asian origin. Like the Health Survey, these studies used measured blood pressure. However, they were based on specific local populations sampled for example from general practitioner lists, or people in work. The large nationally distributed random sample of the Health Survey overcomes some of the potential problems of sample bias in these other studies (for example, in studies based on GP lists, those registered with a doctor might be more likely to self-report than the non-registered; and workplace studies are dealing with a population less likely to have ill health than those who are not working). A study based on self-reporting, which tried to investigate differences among South Asian subgroups, suggested that people from White, Pakistani and Bangladeshi groups report similar rates of diagnosed hypertension, while Indian, African Asian and Chinese informants report lower rates and Black Caribbeans report rates almost 50 percent higher than White informants.8 Ethnic differences in hypertension have also been shown to vary by gender and age. The Health Survey included both self-reported diagnosis of high blood pressure (see Chapter 3, Section 3.2.1) and direct measurements. These two methods are likely to produce different prevalence rates of high blood pressure. There are several possible reasons for this. For instance, in order to obtain a diagnosis of hypertension the informant must have visited the doctor, been able to explain their symptoms, and obtained an answer that they were able to understand and communicate to the interviewer. Language and other communication difficulties are likely to be particularly pertinent for members of some minority ethnic groups. Such issues will not be relevant to the blood pressure measurements. In general, this chapter presents findings based on blood pressure measurement. However, the inclusion of both types of method has also permitted some exploration of differences between self-report and more objective measurement methods. Blood pressure in adults aged 16 and over has been measured in each round of the Health Survey for England since 1991. The main purpose of this chapter is to present distributions of informants' blood pressure by minority ethnic group and age (Sections 7.3 and 7.4). Variations in blood pressure by socio-economic position, using social class of the head of household and equivalised household income (Section 7.5), are also reported. This chapter presents data on informants aged 16 years or over. Blood pressure distributions of those aged under 16 are presented in Chapter 13. 7.2.1 Measurements As in previous years of the Health Survey, blood pressure was measured in informants aged 5 and over using an automated device, the Dinamap 8100 monitor. The detailed protocol for blood pressure measurement is contained in Appendix B. After five minutes' rest, three blood pressure readings were taken on the right arm, using an appropriately sized cuff, with the informant in a seated position. The data presented here are based on the mean of the second and third measurements for informants who had all three recordings completed. Blood pressure was not measured in pregnant women or in those who had drunk alcohol, eaten or smoked in the half hour prior to the nurse visit. Blood pressure data presented here should not be directly compared with blood pressure values obtained using an auscultatory method as the Dinamap is designed against direct intra-arterial criteria of accuracy, rather than against indirect auscultatory measurement criteria.9 The Dinamap tends to provide higher systolic and lower diastolic blood pressure levels than mercury sphygmomanometer fourth phase readings.10,11 In addition, these results should be interpreted with caution as this is a cross-sectional study in which blood pressure was measured at one single point in time. Four blood pressure measurements are presented: systolic blood pressure (SBP); diastolic blood pressure (DBP); mean arterial pressure (MAP), which is derived by adding the level of DBP to one-third of the difference between SBP and DBP; and pulse pressure, derived by subtracting DBP from SBP. 7.2.2 Classification of blood pressure levels Adult informants were classified into one of four groups on the basis of their
SBP and DBP and current use of anti-hypertensive medications. The use
of anti-hypertensive medications was assessed during the nurse visit,
and only if the medicine taken was reported by the informant as having
been prescribed to treat their high blood pressure was the informant
classified as taking anti-hypertensive medication. The four groups are
as follows:
The latter three groups (those who were normotensive treated or hypertensive treated or untreated) were defined as having 'high blood pressure' for the purpose of this report. The threshold of 140/90 mmHg is in accordance with the latest guidelines on hypertension management.12,13,14,15 7.2.3 Response Of those men who were seen by a nurse, the proportion with valid blood
pressure measurements ranged from 76.2% of Bangladeshi men to 89.2%
of Chinese men. The proportion of valid blood pressure measurements
for women ranged from 79.5% of Black Caribbean women to 88.8% of Indian
women. The majority of the remaining informants were excluded because
they had eaten, drunk alcohol or smoked in the half hour before the
nurse interview. 7.3 Blood pressure measurements 7.3.1 Blood pressure measurements in men Although there was little difference between the six minority ethnic groups explored, or between them and the general population, in terms of the four blood pressure measurements used here, there were some significant variations. Unlike the other measures of blood pressure used here, findings for SBP were not normally distributed. Table 7.2 therefore presents median as well as mean SBP measurements, although only mean SBP is reported on. In men, those minority ethnic groups with the youngest age profiles
generally showed lower observed mean blood pressure measurements. In
particular, Bangladeshi and Pakistani men had the lowest observed SBP,
DBP and MAP: SBP was 126.5 mmHg in Bangladeshi men and 129.7 mmHg in
Pakistani men (compared with 136.8 mmHg in men in the general population);
DBP was 72.9 mmHg and 72.6 mmHg respectively (and 76.2 mmHg in the general
population); and MAP was 93.7 mmHg and 94.1mmHg respectively (and 98.9
mmHg in the general population).
After age standardisation, mean SBP in Chinese, Pakistani and Bangladeshi men was significantly lower than for men in the general population, and mean SBP was significantly lower for Bangladeshi men than for men in the other minority ethnic groups. After age standardisation DBP was significantly higher in men of Indian origin than in the general population, while other minority ethnic groups did not differ significantly from the general population. Observed mean pulse pressure was highest among Black Caribbean men (61.6 mmHg)
and lowest among Bangladeshi men (53.6 mmHg). After age standardisation
men of South Asian and Chinese origin showed significantly lower mean
pulse pressure than the general population, while Black Caribbean and
Irish men were not significantly different.
7.3.2 Blood pressure measurements in women Among women from the minority ethnic groups, mean SBP ranged from 120.2 mmHg in Bangladeshis to 130.4 mmHg in Irish women, with the mean for the general population at 132.5 mmHg. Age standardisation confirmed the low mean SBP among Bangladeshi women, and also showed that Chinese women have a significantly lower mean SBP than the general population; Pakistani women by contrast had significantly higher mean SBP.
The observed differences between minority ethnic groups in mean DBP were very small, and after age standardisation none of the groups was significantly different from women in the general population. Observed mean pulse pressure was lowest among Pakistani, Bangladeshi and Chinese
women. After age standardisation, Chinese, Bangladeshi and Indian women
had lower mean pulse pressure than women in the general population.
After age standardisation Black Caribbean women had significantly higher
mean MAP.
In summary, Chinese, Bangladeshi and Indian women had significantly low pulse
pressure, relative to the general population, which is consistent with
the finding among men. Also consistent with the findings for men is
the significantly low SBP of Bangladeshi and Chinese women. 7.3.3 Blood pressure measurements by age Tables 7.3 to 7.6 show mean SBP, DBP, MAP and pulse pressure by age, sex and minority ethnic group. Sex differences in blood pressure measurements were fairly consistent across minority ethnic groups. Women had lower mean SBP and pulse pressure than men among those aged 16-54 in the general population and in each of the minority ethnic groups. Similarly, women had lower mean DBP and MAP than men in every age group, both in the general population and in the minority ethnic groups (with the exception of Pakistani and Chinese informants aged 55 and over, which had sample sizes too small to provide reliable estimates). Also, women had lower mean SBP and pulse pressure in the 16-54 age groups, but experienced higher mean SBP and pulse pressure than their male ethnic counterparts from the age of 55. The relationship between age and blood pressure was also fairly consistent across minority ethnic groups. Mean SBP, DBP and MAP increased with age for men and women in each minority ethnic group. Mean pulse pressure for women also increased with age, but in men it was higher in the youngest and oldest groups than in the middle age group. Tables 7.3, 7.4, 7.5, 7.6 Table 7.7 shows the observed proportion of informants with high blood
pressure (see Section 7.2.2 for definition
of high blood pressure), as well as standardised risk ratios, by minority
ethnic group and gender.
The observed proportions of men with high blood pressure were lower in the Chinese and South Asian groups than among men in the other groups or in the general population. However, after controlling for the effects of age, it was only Bangladeshi and Chinese men who were significantly (almost 25%) less likely to have high blood pressure than men in the general population. While the observed prevalence of high blood pressure in Black Caribbean men was higher than in the general population, this difference was no longer significant once age was controlled for. The observed proportion of women with high blood pressure was lower for each minority ethnic group than it was for women in the general population, with Pakistani and Bangladeshi women having a particularly low observed prevalence of high blood pressure. However, after age-standardisation, the picture was quite different: only Irish women had a lower prevalence of high blood pressure than women in the general population, while Pakistani and Black Caribbean women were significantly more likely to have high blood pressure than women in general. These findings are interesting when compared to earlier studies which
found higher rates of raised blood pressure among Black Caribbean and
South Asian (particularly Pakistani and Bangladeshi) groups.5,6,7
While the findings for women to some extent support those of these earlier
studies, findings for men appear to contradict them. As stated in Chapter 3, the survey also shows the prevalence of medical diagnoses of high blood pressure as reported by informants.
All rates of reported high blood pressure diagnosis were lower than the survey-defined prevalence of high blood pressure, in both sexes and in all minority ethnic groups. In the general population, of those who were found to have survey-defined
high blood pressure, about a third (36.5%) of men and half of women
(48.2%) reported having been told by a doctor or a nurse they had high
blood pressure. This was generally true also among the minority ethnic
groups, with the exception of Black Caribbeans, where a higher proportion
(49.2% of men and 74.3% of women) reported having been diagnosed, and
of South Asian women, who tended to be diagnosed less frequently. After
age standardisation, Black Caribbean men and women and Irish women were
more likely to report that they had been diagnosed as having high blood
pressure than the other minority ethnic groups and the general population.
Bangladeshi men and women and Indian women were the least likely.
Among both men and women, the prevalence of untreated survey-defined
hypertension was generally lower among minority ethnic groups than it
was among the general population as a whole; Irish men were an exception,
as they had a similar prevalence (32.8%) to the general population (32.3%).
After controlling for the effect of age, however, it was only Pakistani,
Bangladeshi and Chinese men, and Black Caribbean and Chinese women,
who were less likely than the general population to have untreated hypertension.
(Table not shown.) The treatment rate for hypertension (defined as the proportion of those with survey-defined high blood pressure who were taking anti-hypertensive medication) for each minority ethnic group is summarised in the table below. Treatment rate among hypertensives Black General
Among men, Black Caribbeans, Indians and Bangladeshis had higher observed treatment rates (34.8%, 29.0% and 28.6%) than the general population, where only about one in five men with high blood pressure were receiving treatment (20.9%); all other minority ethnic groups had rates similar to that of the general population. After age standardisation, Black Caribbean men were more likely to be treated than were men in the general population who had high blood pressure (standardised ratio 1.73). Bangladeshi and Indian men were also significantly more likely to be treated than the general population, while the other minority ethnic groups were not significantly different. Looking at the observed rates among women, over half of Black Caribbean women
with high blood pressure were treated (51.8%), by far the highest treatment
rate among minority ethnic groups of either sex. One third or less of
women with hypertension in all other minority ethnic groups and in the
general population were treated. Age-standardisation confirmed the high
treatment rate of Black Caribbean women (standardised ratio 2.23) while
no significant differences with the general population were observed
for women of other minority ethnic groups. As with SBP and pulse pressure, women in minority ethnic groups tended
to have lower rates of high blood pressure than their male counterparts
in the 16-34 and 35-54 age categories (although because of small sample
bases the differences are not always statistically significant). Among
those aged 55 and over, women and men in the general population were
equally likely to have high blood pressure, a pattern which was also
apparent among the other minority ethnic groups (although the analysis
amongst this age category is limited because of very small sample bases
for some of the groups).
7.5.1 Social class of head of household Table 7.9 shows observed blood pressure levels and standardised risk ratios for high blood pressure by social class of head of household within minority ethnic group. There was no consistent pattern of difference across minority ethnic groups between men in manual and non-manual social classes. In some groups the age-standardised prevalence of high blood pressure was significantly higher among manual social classes (for example, Bangladeshi and Indian men), while in others the reverse was the case (Chinese men). In the case of women, previous Health Surveys have shown a relationship
between social class and high blood pressure for women in the general
population.16 Results from the 1999 Health Survey show some
evidence of a similar tendency for women in minority ethnic groups.
The prevalence of age-standardised high blood pressure was higher in
manual than non-manual social classes, with the difference reaching
significance in some groups (Indian and Chinese women, and the general
population) but not in all. 7.5.2 Equivalised household income Table 7.10 shows blood pressure levels by equivalised household income tertile
within minority ethnic group. In general, there was no apparent relationship
between high blood pressure and income for these minority ethnic groups.
There were, however, exceptions to this. Chinese women and Pakistani
men appeared to experience a reduced risk of high blood pressure with
increasing equivalised household income (as did women in the general
population). Indian men and Irish women in the highest income tertile
were significantly less likely to have high blood pressure. References and notes 1 MacMahon S, Peto R, Cutler J, et al. Blood pressure, stroke, and coronary heart disease I: prolonged differences in blood pressure: prospective observational studies corrected for the regression dilution bias. The Lancet 1990; 335:765-74. 2 Collins R, Peto R, MacMahon S, et al. Blood pressure, stroke, and coronary heart disease II: short-term reductions in blood pressure: overview of randomised drug trials in their epidemiological context. The Lancet 1990; 335:827-38. 3 Stamler J, Stamler R, Neaton JD. Blood pressure, systolic and diastolic, and cardiovascular risks. Arch Intern Med 1993; 153:598-615. 4 Collins R, MacMahon S. Blood pressure, antihypertensive drug treatment and the risks of stroke and of coronary heart disease. Br Med Bull 1994; 50:272-298. 5 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; 78:555-563. 6 Chaturvedi N, McKeigue PM, Marmot MG. Resting and ambulatory blood pressure differences in Afro-Caribbeans and Europeans. Hypertension 1993; 22:90-96. 7 Cruickshank JK, Jackson SH, Bannan LT, Beevers DG, Beevers M, Osbourne VL. Blood pressure in black, white and Asian factory workers in Birmingham. Postgrad Med J 1983; 59:622-626. 8 Nazroo JY. The Health of Britain's Ethnic Minorities. Policy Studies Institute, London, 1997. 9 O,Brien E, Fitzgerald D, O'Malley K. Blood pressure measurement: current practice and future trends. Br Med J 1985; 290:729-734. 10 Weaver MG, Park MK, Lee KH. Differences in Blood Pressure Levels Obtained by Auscultatory and Oscillometric Methods. AJDC 1990; 144:911-914. 11 Bolling K. Dinamap 8100 calibration study, OPCS. HMSO, London, 1994. 12 Joint National Committee on Prevention, Detection, Evaluation and Treatment of High Blood Pressure and the National High Blood Pressure Education Program Coordinating Committee. The sixth report of the Joint National Committee on prevention, detection, evaluation, and treatment of high blood pressure. Arch Intern Med 1997; 157:2413-2446. 13 1999 World Health Organization - International Society of Hypertension Guidelines for the Management of Hypertension. J Hypertens 1999; 17:151-183. 14 Ramsay LE, Williams B, Johnston GD, MacGregor GA, Poston L, Potter JF, Poulter NR, Russell G. British Hypertension Society guidelines for hypertension management 1999: Summary. BMJ 1999; 319:630-635. 15 Modern Standards and Service Models: National Service Framework for Coronary Heart Disease. Stationery Office, London, 2000. 16 Boreham R, Erens B, Falaschetti E, Hirani V, Primatesta P. Risk factors for cardiovascular disease (Chapter 3) in Erens B and Primatesta P. (eds) Health Survey for England 1998, The Stationery Office, London, 1999. 7.1 Response to blood pressure measurement, by minority ethnic group 7.2 Blood pressure measurements, by minority ethnic group 7.3 Systolic blood pressure (SBP), by age within minority ethnic group 7.4 Diastolic blood pressure (DBP), by age within minority ethnic group 7.5 Mean arterial pressure (MAP), by age within minority ethnic group 7.6 Pulse pressure, by age within minority ethnic group 7.7 Blood pressure levels, by minority ethnic group 7.8 Blood pressure levels, by age within minority ethnic group 7.9 Blood pressure levels, by social class of head of household within minority ethnic group 7.10 Blood pressure levels,
by equivalised household income tertile within minority ethnic group
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