Anne McMunn, Marion Brookes, Emanuela Falaschetti, Paola Primatesta
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SUMMARY
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It is well known that coronary heart disease (CHD) and stroke, which are important sources of morbidity in Scotland (see Chapter 2), are positively associated with both systolic and diastolic blood pressure.1,2,3 The control of high blood pressure is, therefore, an important element in the reduction of cardiovascular disease. 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 Scottish Health Survey is the only survey to provide data on blood pressure based on a nationally representative sample of Scottish adults. The 1998 Health Survey is the first to provide this data also for children (aged 5-15) and for older adults (aged 65-74). The purpose of this chapter is to describe blood pressure levels and the prevalence of high blood pressure for the Scottish population in 1998. Variations in blood pressure between regions and social classes will be examined for both adults and children. Trends in adult blood pressure since 1995 will be presented and comparisons between Scotland and England will be made using blood pressure results from the 1998 Health Survey for England.
12.2.1 Measurement method
Blood pressure was measured in informants aged 5-74 using an automated device, the Dinamap 8100 monitor. Three blood pressure readings were taken on the right arm with the informant in a seated position after five minutes rest. Blood pressure of pregnant women was not measured. The detailed protocol for blood pressure measurement is contained in Appendix B in Volume 2. The data presented here are based on the mean of the second and third readings from informants in whom all three recordings were completed. Blood pressure data collected using a Dinamap should not be compared directly with blood pressure values obtained using the standard sphygmomanometer as the two methods tend to give somewhat different readings.5
Blood pressure is known to have a stronger relationship with age, height and weight in children than in adults.6,7,8 This is reflected in the most recent guidelines on high blood pressure in children which take account of both specific age year and height percentile.9 Consequently, children's blood pressure values in this chapter are always presented by height tertile or are height-standardised.
12.2.2 Classification of blood pressure levels
Adult informants were classified into one of four groups on the basis of their systolic (SBP) and diastolic (DBP) blood pressure and current use of anti-hypertensive medications as follows:
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Normotensive-untreated |
SBP <140 mmHg and DBP <90 mmHg, not currently taking any anti-hypertensive drug(s) |
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Normotensive-treated |
SBP <140 mmHg and DBP <90 mmHg, currently taking anti-hypertensive drug(s) |
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Hypertensive-treated |
SBP ³ 140 mmHg and/or DBP ³ 90 mmHg, currently taking anti-hypertensive drug(s) |
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Hypertensive-untreated |
SBP ³ 140 mmHg and/or DBP ³ 90 mmHg, not currently taking any anti-hypertensive drug(s) |
The latter three groups (those who are normotensive treated or hypertensive treated or untreated) are defined as having 'high blood pressure' for the purpose of this report.
This year, the survey's SBP and DBP threshold for adult high blood pressure has been changed from 160/95 mmHg ('old' definition) to 140/90 mmHg ('new' definition), in accordance with the latest guidelines on hypertension management.10,11,12 The potential benefit of drug treatment in patients with blood pressure in the range 140-159 mmHg SBP and 90-94 mmHg DBP may be questionable. However, it is clear from studies that have followed people over time that blood pressures in this range are associated with increased risk, particularly among individuals who also have additional cardiovascular risk factors, such as high lipid levels, diabetes or target organ damage.13 For this report the adult prevalence of high blood pressure, rates of treatment and control, and trends in blood pressure levels between 1995 and 1998 (Tables 12.12 -12.14, 12.26) will all be presented using both the old and new thresholds for hypertension. Tables presenting 1998 regional and social class differences and differences between Scotland and England in the prevalence of high blood pressure (Tables 12.17, 12.18, 12.22, 12.23, 12.29) will use only the 'new' definition of high blood pressure.
Currently, the guidelines which are most widely used for blood pressure in children are those published in 1996 by the National High Blood Pressure Education Program Working Group on Hypertension Control in Children and Adolescents in the USA.14 These 1996 guidelines define high blood pressure as values above the 95th percentile of a child's age, sex and height specific curve. High normal rates fall between the 90th and 95th percentiles. The 90th and 95th percentiles for children's blood pressure are included in this chapter. No direct comparisons with the American curves are possible because the US measurements were obtained using a sphygmomanometer in more ethnically diverse samples than the Scottish Health Survey sample.
12.2.3 Rates of successful measurement
Valid blood pressure readings were obtained from 6,758 adults (3,031 men and 3,727 women) and 2,120 children (1,066 boys and 1,054 girls), which is 90.7% of all adults and 84.1% of all children visited by a nurse. Rates of successful measurement were slightly lower for women aged 16-44 because 66 (3%) of them were excluded due to pregnancy. Among children, response rates were equal for boys and girls. Rates were slightly higher for boys aged 10-15 than for boys aged 5-9. Rates rose with age for girls.
Among adult informants who had three valid blood pressure readings, 461 men and 634 women were taking one or more anti-hypertensive agents that may affect blood pressure readings. Of these, 34.5% of men and 53.1% of women were on diuretics, 42.9% of men and 36.5% of women were on beta-blockers, 26.3% of men and 21.5% of women were taking ACE inhibitors and 38.4% of men and 28.8% of women were on calcium antagonists. (It should be noted that these categories of medicine are not mutually exclusive). Informants who were taking any of these medications are included in each of the tables for this chapter (unless otherwise stated).
12.3 BLOOD PRESSURE BY AGE AND SEX
12.3.1 Systolic blood pressure (SBP)
Mean SBP was 132.4 mmHg for men and 127.4 mmHg for women aged 16-74. As expected, mean SBP increased continuously with age for both men and women. Mean SBP for men ranged from 125.0 mmHg in those aged 16-24 to 145.0 mmHg in those aged 65-74 and for women ranged from 116.7 mmHg in the 16-24 age group to 148.5 mmHg for the 65-74 age group. Men had higher mean SBP than women in all but the 65-74 age group in which women had higher mean SBP. Similarly, in this age group women were more likely than men to have an SBP reading of 180 mmHg or higher (7.7% compared with 4.2%).
Blood pressure in children is known to be positively and independently associated with both age and height.14,15,16,17,18 As expected, mean SBP rose with age and height for both boys and girls. Mean SBP rose from 104.7 mmHg in boys aged 5-6 to 116.0 in boys aged 13-15. For girls, mean SBP rose from 104.5 mmHg in the 5-6 age group to 112.0 mmHg in the 13-15 age group. There were no substantial sex differences in children's SBP.
12.3.2 Diastolic blood pressure (DBP)
Mean DBP was 73.5 mmHg for men and 69.5 mmHg for women aged 16-74. Mean DBP rose with age until the 55-64 age group where it reached 79.8 mmHg for men and 73.9 mmHg for women, and then dropped slightly in the 65-74 age group. Mean DBP was higher for men than women in all but the youngest age group, where there was no difference.
Mean DBP was 55.8 mmHg for boys and 56.4 mmHg for girls. There was no clear relationship between mean DBP and age, height or sex in children's mean DBP.
12.3.3 Pulse pressure
Pulse pressure is derived by subtracting DBP from SBP. Mean pulse pressure was 58.9 mmHg for men and 57.9 mmHg for women. Mean pulse pressure decreased from the 16-24 age group to the 35-44 age group and then increased with age for both men and women (peaking at 67.0 mmHg for men and 75.1 mmHg for women aged 65-74). Men had higher mean pulse pressure than did women among the 16-44 age groups, but women had higher mean pulse pressure than men in those aged 45-74.
Mean pulse pressure increased with age and slightly with height for both boys and girls. Mean pulse pressure rose from 48.7 mmHg in boys aged 5-6 to 61.1 in boys aged 13-15. For girls, mean pulse pressure rose from 48.8 mmHg in the 5-6 age group to 55.8 mmHg in the 13-15 age group.
12.3.4 Mean arterial pressure (MAP)
Mean arterial pressure is defined as the sum of the level of DBP plus one third of the difference between SBP and DBP. Mean MAP increased with age in both sexes. Mean MAP rose from 86.8 mmHg in men aged 16-24 to 103.7 mmHg in men aged 65-74 and from 83.5 mmHg in women aged 16-24 to 101.2 mmHg in women aged 65-74. Mean MAP was higher for men than women in each age group.
Mean MAP rose slightly with age for both boys and girls. Mean MAP rose from 75.9 mmHg in boys aged 5-6 to 79.2 mmHg in boys aged 13-15. For girls, mean MAP rose from 75.1 mmHg in the 5-6 age group to 78.5 mmHg in the 10-12 age group and 78.2 mmHg 13-15 age group. There was virtually no increase in mean MAP with height.
12.4 BLOOD PRESSURE LEVELS AND CONTROL
12.4.1 High blood pressure
Using the 'old' definition, the prevalence of high blood pressure was 17.2% for men and 17.9% for women in 1998. The prevalence increased with age for both men and women. It rose from 1.8% of men aged 16-24 to 51.5% of men aged 65-74, while for women it rose from 0.5% in the 16-24 age group to 58.1% in the 65-74 age group.
Using the 'new' definition, the prevalence of high blood pressure was 33.1% for men and 28.4% for women. As with the 'old' definition of high blood pressure, the prevalence increased with age for both men and women. It rose from 9.8% of men aged 16-24 to 73.5% of men aged 65-74, while for women it rose from 3.5% in the 16-24 age group to 75.5% in the 65-74 age group.
The prevalence of high blood pressure was higher for men than for women in those aged 16-54 using the 'old' definition and in those aged 16-64 using the 'new'. This sex difference was larger when using the 'new' definition than when using the 'old'. Most of the sex difference was concentrated among untreated hypertensive informants.
Table 12.12, Figure 12A
Figure 12A Prevalence of high blood pressure using pre-1998 definition by age and sex
Figure 12A Prevalence of high blood pressure using the 1998 definition, by age and sex
12.4.2 Treatment and control of high blood pressure
Using the 'old' definition of high blood pressure, the treatment rate (defined as the proportion of those with survey-defined high blood pressure who are taking anti-hypertensive medication) was 66.5% for men and 72.3% for women. Changing to the 'new' definition of high blood pressure reduced the proportion of those on treatment to 34.5% for men and 45.5% for women. Among those aged 16-64, women were more likely than men to have their high blood pressure treated, particularly when the 'new' definition for high blood pressure is used, while men were more likely than women to have their high blood pressure treated among those aged 65-74. Treatment rates were higher for informants aged 45-74 than for those aged 16-44, particularly when using the 'new' definition of high blood pressure.
Among those who were on anti-hypertensive medication, the rate of successful control (defined as those taking anti-hypertensive medication who had blood pressure readings below the survey defined levels for high blood pressure) using the 'old' definition of high blood pressure (SBP < 160 mmHg and DBP < 95 mmHg) was 79.5% in men and 79.7% in women. The control rate using the 'new' definition of high blood pressure (defined as the proportion of those taking anti-hypertensive medication who had SBP < 140 mmHg and DBP < 90 mmHg) was 46.7% in men and 46.9% in women. Treatment appeared to be less effective in controlling high blood pressure in informants aged 65-74 than in the younger age groups for both men and women and using either the 'new' or 'old' definitions of high blood pressure to determine the control rate.
12.5 BLOOD PRESSURE AND REGION
12.5.1 Region and mean systolic and diastolic blood pressure
Table 12.15 shows mean SBP and mean DBP by region. As was the case in 1995, regional differences were small for both mean SBP and mean DBP before adjusting for age. Unadjusted mean SBP ranged from 130.3 mmHg to 134.9 mmHg for men and from 125.7 mmHg to 130.3 mmHg for women. Grampian & Tayside (and Forth Valley, Argyll & Clyde for women) had the lowest unadjusted mean SBP while the Highland & Islands had the highest for both men and women. Among men, unadjusted mean DBP ranged from 72.4 mmHg in Grampian & Tayside to 74.8 mmHg in the Highland & Islands. For women, unadjusted mean DBP ranged from 68.0 mmHg in Grampian & Tayside to 71.5 mmHg in the Highland & Islands.
On adjustment for age, using linear regression, significant variations in mean SBP between regions were found for women (p<0.001) but not for men (p=0.236). For women, mean SBP was 2.5 mmHg lower than the overall mean in Forth Valley, Argyll & Clyde and 1.3 mmHg lower than the overall mean in Grampian and Tayside. Women's mean SBP was highest in the Highland & Islands at 2.7 mmHg greater than the overall mean SBP and also higher, by 1.5 mmHg, in Lanarkshire, Ayrshire & Arran. For men, mean SBP was 1.6 mmHg lower in Grampian & Tayside, but there were no other significant regional differences in mean SBP.
With DBP, after adjusting for age using linear regression, there were significant regional variations in mean DBP for women (p=0.001) but not for men (p=0.245). Women's mean DBP was 1.8 mmHg higher than the overall mean in the Highland & Islands and 1.2 mmHg lower than the overall mean in Grampian & Tayside.
12.5.2 Region and high blood pressure
The prevalence of high blood pressure (using the 'new' definition) by region, age and sex is shown in Tables 12.17 and 12.18. There were no large regional differences in the prevalence of high blood pressure. Age-standardised prevalence varied from 27.9% in Grampian & Tayside to 34.9% in Borders, Dumfries & Galloway for men and from 25.5% in Lothian & Fife to 31.5% in the Highland & Islands for women.
12.5.3 Region and child blood pressure
Table 12.19 shows regional variation in children's mean SBP and mean DBP (height-standardised). The four age groups used in previous tables of child blood pressure were combined to two age groups for this and subsequent tables on child blood pressure due to the small number of children in some of the groups.
Regional differences in children's blood pressure were small. Boys' mean SBP ranged from 107.7 mmHg in Borders, Dumfries & Galloway to 111.5 mmHg in Lothian & Fife while boys' mean DBP ranged from 54.5 mmHg in Greater Glasgow to 57.0 mmHg in Lanarkshire, Ayrshire & Arran. Both mean SBP and mean DBP were slightly lower for boys in Borders, Dumfries & Galloway and in Greater Glasgow than in other regions.
There was no significant regional variation in girls' blood pressure. Girls' mean SBP ranged from 107.9 mmHg in the Forth Valley, Argyll & Clyde region to 111.4 mmHg in the Highland & Islands region. Girls' mean DBP ranged from 55.3 mmHg in the Forth Valley, Argyll & Clyde region to 57.5 mmHg in the Highland & Islands region.
12.6 BLOOD PRESSURE AND SOCIAL CLASS
12.6.1 Mean systolic and diastolic blood pressure and social class
Table 12.20 shows mean SBP and mean DBP by social class. Social class is defined by the occupation of the chief income earner in the informant's household (see Appendix E in Volume 2 for details). There were no social class variations in mean SBP or mean DBP for men or women when unadjusted for age.
On adjustment for age, using linear regression, there were no significant social class variations in mean SBP or mean DBP for men (p=0.220 for SBP and p=0.562 for DBP) or women (p=0.276 for SBP and p=0.121 for DBP).
12.6.2 High blood pressure and social class
The prevalence of high blood pressure, using the 'new' definition, by social class, age and sex is shown in Tables 12.22 and 12.23. There was no social class gradient in the age-adjusted prevalence of high blood pressure for men. For women, the age-adjusted prevalence of high blood pressure was lowest in Social Class I (16.7%) and highest in Social Class V (33.6%) with a very slight increase with social class between these two.
12.6.3 Child blood pressure and social class
Table 12.24 shows social class variation in children's mean SBP and mean DBP (height-standardised). For this table, Social Classes I and II and IV and V have been combined due to the small number of children in some of the groups. There did not appear to be any social class gradient in mean SBP or mean DBP for boys or girls.
12.7 TIME TRENDS IN ADULT BLOOD PRESSURE: 1995 AND 1998
12.7.1 Time trends in mean systolic and diastolic blood pressure
Blood pressure trends over time can be presented only for informants aged 16-64 as children and people aged 65-74 were not included in the 1995 survey. Overall, there was no significant change in mean SBP or mean DBP between 1995 and 1998 in Scotland, either for men or for women.
12.7.2 Time trends in high blood pressure
Using the 'old' definition of high blood pressure, the prevalence of high blood pressure appeared to increase slightly for men in the oldest and youngest age groups (from 33.6% to 38.1% for those aged 55-64 and from 0.4% to 1.8% in those aged 16-24). Conversely, the prevalence of survey-defined high blood pressure seemed to decrease slightly for women in the middle age groups (25-54).
Using the 'new' definition of high blood pressure, the prevalence of high blood pressure again increased slightly for men in the oldest age group (from 57.5% to 61.8%). In women in the 25-54 age groups the decrease was much smaller using the 'new' rather than the 'old' definition.
12.8 BLOOD PRESSURE IN SCOTLAND AND ENGLAND
12.8.1 Comparability of blood pressure in the two surveys
This section compares the 1998 blood pressure results in Scotland with those from the 1998 Health Survey for England (HSE). Scottish results are compared with England as a whole as well as with Northern England which is comprised of the two regional health authorities of Northern & Yorkshire and North West.
The surveys for Scotland and England are similar in design. Blood pressure data are collected using exactly the same equipment and measurement protocols. Also, the same research personnel train the nurses working in Scotland and England. As a result, it is very unlikely that there are any systematic differences in the measurement of blood pressure between the two surveys.
Response rates to the blood pressure measurements were broadly similar between the two countries with the exception of 5-6 year old girls who had a lower response rate in Scotland. (Response rates for England are not shown).
12.8.2 Comparison of adult systolic and diastolic blood pressure
Mean SBP was slightly lower in Scotland than in England. Men's mean SBP was about 3 mmHg lower in Scotland than in England overall, ranging from 1.1 to 3.4 mmHg lower across age groups. The difference decreased for women from 3.4 and 3.6 mmHg lower in Scotland for the two youngest age groups to 0.7 mmHg lower in those aged 65-74. Differences between Scotland and Northern England were smaller than those for England as a whole and were only evident for the 16-44 age group. These differences are much smaller than those found in 1995, especially in comparison with the Northern Region. This reflects reductions in mean SBP in England rather than increases in mean SBP in Scotland. Variations in median SBP followed the same patterns as those for mean SBP.
Mean DBP was lower in Scotland than in England for both men (73.5 mmHg compared with 76.0 mmHg) and women (69.5 mmHg compared with 71.7 mmHg) and across all age groups. As with SBP, DBP values were much lower in Northern England than in England as a whole; hence differences between Scotland and Northern England were smaller than the differences between Scotland and England as a whole. Median DBP followed a pattern similar to mean DBP.
12.8.3 Comparison of high blood pressure
The prevalence of high blood pressure is compared using the 'new' definition (that is, normotensive treated, hypertensive treated or hypertensive untreated, with hypertensive defined as SBP > 140 mmHg or DBP > 90 mmHg). Overall, the prevalence of high blood pressure was lower in Scotland than in England for both men (33.1% in Scotland and 40.1% in England) and women (28.4% in Scotland and 29.4% in England), the differences being much larger for men than for women. The prevalence of high blood pressure was also lower in Scotland than England for all age groups for men and for all but the 45-64 age group for women. With one age-group exception (65-74), the prevalence of high blood pressure (using the 'new' definition) was lower in Scotland than in Northern England for men with no consistent pattern of differences across the age groups for women.
While rates of cardiovascular mortality tend to be higher in Scotland than in England, both mean SBP and DBP as well as the prevalence of high blood pressure are lower in Scotland than in England. Similar results were found in the 1995 surveys: then, mean blood pressure was lower in Scotland than in England and the prevalence of high blood pressure was lower in Scotland once treatment rates were taken into account.19 These results indicate that factors other than blood pressure may be associated with higher levels of ischaemic heart disease and stroke in Scotland. For instance, Scottish smokers appear to smoke more than English smokers (see Chapter 8), diets appear to be slightly poorer in Scotland (see Chapter 10), and physical activity levels are lower in Scotland than in England among those aged 55-74 (see Chapter 6).
12.8.4 Comparison of children's blood pressure
Children's blood pressure was slightly lower in Scotland than in England or Northern England, but not by much. For boys, mean SBP in Scotland was 0.3 mmHg lower than in England and 0.9 mmHg lower than in Northern England. Boys mean DBP in Scotland was 0.6 mmHg lower than in England as a whole and 0.3 mmHg lower than in Northern England. Among girls, mean SBP in Scotland was 0.6 mmHg lower than in England and 0.5 mmHg lower than in Northern England. Mean DBP in Scotland for girls was 1.0 mmHg lower than in England and 1.1 mmHg lower than in Northern England. This relationship was not consistent for all age groups. For girls aged 5-9, both mean SBP and mean DBP were higher in Scotland than in Northern England, while for boys aged 5-9 mean SBP was higher in Scotland than in England as a whole.
Median SBP and DBP followed similar patterns to mean SBP and DBP. Median SBP and DBP were lower in Scotland than in England or Northern England for both boys and girls overall and for both boys and girls in the 10-15 age group. However, median SBP was highest in Scotland and median DBP was higher in Scotland than in England as a whole for boys aged 5-9. Also, median SBP was higher in Scotland than in both Northern England and England as a whole and median DBP was higher in Scotland than in Northern England for girls aged 5-9.
Figure 12B Adults's mean systolic blood pressure for Scotland, England and Northern England, by age and sex
Figure 12B Children's mean systolic blood pressure for Scotland, England and Northern England, by age and sex
