Patterns of coronary heart disease mortality over the 20th century in England and Wales: Possible plateaus in the rate of decline

1471-2458-8-148 1471-2458 Research article Patterns of coronary heart disease mortality over the 20th century in England and Wales: Possible plateaus in the rate of decline Allender Steven steven.allender@dphpc.ox.ac.uk Scarborough Peter peter.scarborough@dphpc.ox.ac.uk O'Flaherty Martin moflaher@liv.ac.uk Capewell Simon capewell@liverpool.ac.uk

Division of Public Health and Primary Health Care, University of Oxford, Oxford, UK

Division of Public Health, University of Liverpool, UK

BMC Public Health 1471-2458 2008 8 1 148 http://www.biomedcentral.com/1471-2458/8/148 18452595 10.1186/1471-2458-8-148 06 9 2007 01 5 2008 01 5 2008 2008 Allender et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Background

Coronary heart disease (CHD) rates in England and Wales between 1950 and 2005 were high and reasonably steady until the mid 1970s, when they began to fall. Recent work suggests that the rate of change in some groups has begun to decrease and may be starting to plateau or even reverse.

Methods

Data for all deaths between 1931 and 2005 in England and Wales were grouped by year, sex, age at death and contemporaneous ICD code for CHD as cause of death. CHD mortality rates by calendar year and birth cohort were produced for both sexes and rates of change were examined.

Results

The pattern of increased burden of CHD mortality within older age groups has only recently emerged in men, whereas it has been established in women for far longer. CHD mortality rates among younger people showed little variation by birth cohort. For younger women (49 and under), the rate of change in CHD mortality has reversed in the last 20 years, indicating a future plateau and possible reversal of previous improvement in CHD mortality rates. Among younger men the rate of change in CHD mortality has been consistent for the past 15 years indicating that rates in this group have continued to fall steadily.

Conclusion

Although CHD mortality rates continue to drop in older age groups the actual burden of coronary heart disease is increasing due to the ageing of the population. The rate of improvement in CHD mortality appears to be beginning to decline and may even be reversing among younger women.

Background

Cardiovascular disease appears set to continue as the dominant cause of death and disability in the UK. Age-standardised coronary heart disease (CHD) rates in England and Wales were high between 1950 and the mid 1970s. After this time CHD mortality rates began to fall and have been falling since 1. Age-standardisation of CHD mortality rates allows for direct comparison between different time periods, when the age structure of England and Wales were significantly different. However, little work has been done on long term trends in age-stratified CHD mortality rates. One recent study suggested a period effect: that patterns in CHD mortality rates between 1920 and 1986 were similar for diverse age groups and, while rates were higher in higher age groups, all age groups experienced a peak in the mid 1970s 2. Closer examination of age-stratified rates is very important because, when only age-standardised rates are considered, reductions in the mortality rate in older age groups may obscure less positive trends in younger men and women.

The recent trends in cardiovascular risk factor prevalence in younger people are disturbing. Obesity levels in people aged 45 and under have been rising for over ten years, and there has been a similar increase in type 2 diabetes. Physical activity levels in younger people decreased slightly over the last fifteen years, and smoking levels within this age group have remained high, with approximately 25% of men and 20% of women under 45 smoking 3. These adverse trends could begin to slow, or even reverse, the previously observed decline in mortality rates within younger age groups. Evidence from Australia 4 and America 5 suggests some levelling out of CHD mortality rates among younger men and women and warn that CHD mortality rates in these groups may be starting to increase.

Studying the patterns of mortality over time for chronic disease is important. Firstly, to assess whether current disease reduction strategies are proving to be successful. Secondly, to allow inferences to be made about the contribution of different population factors to disease risk. It is useful to examine long term trends as this allows for recent trends to be viewed in perspective as well as providing a history of the disease burden. As well as recording age-stratified mortality rates over time, it is also useful to record patterns in the number of CHD deaths experienced by different age groups. Such patterns allow for an estimate of the burden of CHD that incorporates the dynamics of an ageing population which are otherwise obscured by declining mortality rates.

A useful alternative to recording trends by calendar year is to examine the experiences of different birth cohorts. This approach allows for a direct comparison of CHD mortality rates within different generations. Such a method can be used to compare the effect of environmental exposures over the whole life course, or those which are typical for a given generation 6.

Recording long-term CHD mortality trends requires use of different definitions for CHD drawn from different International Classification of Diseases (ICD) revisions. Inconsistencies in definitions between revisions effectively limits the potential time period under consideration; it is generally agreed that reliable coding of CHD did not begin until the fourth ICD revision (in 1931) 7. Reasonably consistent definitions have existed since the seventh ICD revision in 1967 8. Because of discontinuities in trends due to definition revisions the patterns in CHD mortality from the first half of the twentieth century should be treated with caution.

This paper therefore examines the variation in CHD mortality by calendar year and by birth cohort for all registered deaths between 1931 and 2005 in England and Wales with a particular focus on recent trends for the younger age groups.

Methods

Data on all deaths in England and Wales in the twentieth century by year, sex, age at death and contemporaneous ICD code for cause of death were provided by the Office for National Statistics, along with population estimates for each year-age-sex group. These data were accompanied by data on population estimates, and the number of CHD deaths by age and sex for 2001 to 2005. The data used in this study were subject to previous ethical review within the Office for National Statistics. Separate ethics approval was not considered necessary for this analysis.

A review of literature considering long term trends in CHD produced a framework for the coding of CHD over different revisions of the ICD 67910. Where there was ambiguity over ICD codes one of the authors (SC), a researcher with extensive experience in heart disease, provided a final decision on CHD codes. A coding frame for CHD incorporating ICD revisions 4 to 10 was constructed and is shown in Table 1. This coding frame was used to reduce the twentieth century data to deaths from CHD since 1931.

Table 1

Coding frame for coronary heart disease, 1931 to 2005

ICD revision

ICD code

Primary description

Secondary description

ICD-4

Diseases of the coronary arteries, Angina pectoris

ICD-5

94b

Angina pectoris without mention of coronary disease

ICD-5

94a

Diseases of the coronary arteries

ICD-6

4202

Arteriosclerotic heart disease, including coronary disease

Angina pectoris without mention of coronary disease

ICD-6

4201

Arteriosclerotic heart disease, including coronary disease

Heart disease specified as involving coronary arteries

ICD-6

4200

Arteriosclerotic heart disease, including coronary disease

Arteriosclerotic heart disease so described

ICD-7

4202

Arteriosclerotic heart disease, including coronary disease

Angina pectoris without mention of coronary disease

ICD-7

4201

Arteriosclerotic heart disease, including coronary disease

Heart disease specified as involving coronary arteries

ICD-7

4200

Arteriosclerotic heart disease, including coronary disease

Artetriosclerotic heart disease so described

ICD-8

4149

Asymptomatic ischaemic heart disease

Without mention of hypertensive disease

ICD-8

4140

Asymptomatic ischaemic heart disease

With hypertensive disease

ICD-8

4139

Angina pectoris

Without mention of hypertensive disease

ICD-8

4130

Angina pectoris

With hypertensive disease

ICD-8

4129

Chronic ischaemic heart disease

Other endocardial structures

ICD-8

4124

Chronic ischaemic heart disease

Cardiovascular disease without mention of hypertension or chronic ischaemic heart disease

ICD-8

4123

Chronic ischaemic heart disease

Chronic ischaemic heart disease with no mention of hypertension

ICD-8

4122

Chronic ischaemic heart disease

Cardiovascular disease with hypertension but no mention of chronic ischaemic heart disease

ICD-8

4121

Chronic ischaemic heart disease

Chronic ischaemic heart disease with hypertension

ICD-8

4120

Chronic ischaemic heart disease

ICD-8

4119

Other acute and sub-acute forms of ischaemic heart disease

Without mention of hypertensive disease

ICD-8

4110

Other acute and sub-acute forms of ischaemic heart disease

With hypertensive disease

ICD-8

4109

Acute myocardial infarction

Without mention of hypertensive disease

ICD-8

4100

Acute myocardial infarction

With hypertensive disease

ICD-9

4149

Other forms of chronic ischaemic heart disease

Unspecified

ICD-9

4148

Other forms of chronic ischaemic heart disease

Other

ICD-9

4141

Other forms of chronic ischaemic heart disease

Aneurysm of heart

ICD-9

4140

Other forms of chronic ischaemic heart disease

Coronary atherosclerosis

ICD-9

4130

Angina pectoris

ICD-9

4120

Old myocardial infarction

ICD-9

4110

Other acute and subacute forms of ischaemic heart disease

ICD-9

4100

Acute myocardial infarction

ICD-10

I20

Angina pectoris

ICD-10

I21

Acute myocardial infarction (AMI)

ICD-10

I22

Subsequent myocardial infarction

ICD-10

I23

Certain current complications following AMI

ICD-10

I24

Other acute ischaemic diseases

ICD-10

I25

Chronic ischaemic heart disease

The age-stratified number of CHD deaths, and the age-stratified CHD mortality rate (number of deaths/population) for men and women by calendar year were tabulated and graphed. The rate of change in CHD mortality rates was tracked by calculating the percentage difference between two sequential years, using moving five year averages for smoothing. The rate of change was tabulated and graphed by calendar year.

Ten year birth cohorts were constructed by subtracting the mean age of each five year age band from the year of death. The population for each birth cohort was derived within gender and age groups from annual population figures. Age-stratified CHD mortality rates were estimated as the number of CHD deaths within these groups, divided by the population. Confidence intervals for rates were calculated using the method described by Altman 11. It should be noted that mortality rates for ages 30–34 and 35–39 within the 1895–1904 birth cohort were calculated using CHD mortality deaths that occurred from 1931 onwards. Age-stratified population levels for this cohort were calculated in a similar way as for other birth cohorts.

Results

Age-stratified CHD mortality rates for men and women by calendar year are shown in Figure 1. They show a consistent pattern, both within age groups and gender, of a sharp increase until the mid 1970s, and then a steady decline. A sharp rise in the CHD mortality rate for both men and women is evident in 1967, the first year of the ICD-7 revision.

Figure 1

Crude CHD death rates and mortality rate per 100,000, by age group (45 and older), men and women, 1931 to 2005

Crude CHD death rates and mortality rate per 100,000, by age group (45 and older), men and women, 1931 to 2005.

Figure 1 also shows the number of CHD deaths in older age groups of men and women by calendar year. The pattern of a higher burden of CHD mortality for older age groups has only recently emerged in men, whereas it has been established in women for far longer. As an example the CHD death rate among women aged 80–84 exceeded that for women age 60–64 for the first time in 1949, a phenomenon which did not occur in the same age groups in men until 1985 (Table 2).

Table 2

Coronary heart disease deaths, mortality rate, rate ratio and 95% confidence intervals for rate ratios by sex, age and birth cohort

Men

30–34

35–39

40–44

45–49

50–54

55–59

60–64

65–69

Deaths

1895–1904

162

851

3113

10759

28186

55648

92238

127362

1905–1914

306

1757

7127

19881

43720

77885

115431

150718

1915–1924

955

3943

11902

28017

51781

78397

106744

128117

1925–1934

1461

5170

13436

26591

43228

58544

72621

81940

Population (000s)

1895–1904

1669

1566

1598

1587

1524

1435

1292

1091

1905–1914

1683

1693

1688

1626

1562

1480

1337

1142

1915–1924

1728

1705

1696

1657

1602

1511

1383

1214

1925–1934

1533

1545

1523

1490

1436

1364

1259

1117

Mortality rate per 100,000

1895–1904

195

678

1850

3877

7139

11670

1905–1914

104

422

1223

2799

5264

8634

13201

1915–1924

231

702

1690

3232

5190

7719

10557

1925–1934

335

882

1785

3011

4293

5770

7334

95% CI mortality rate per 100,000

1895–1904

(8, 11)

(51, 58)

(188, 202)

(665, 691)

(1828, 1872)

(3846, 3909)

(7094, 7183)

(11609, 11730)

1905–1914

(16, 20)

(99, 109)

(412, 432)

(1206, 1240)

(2773, 2825)

(5228, 5300)

(8586, 8681)

(13139, 13263)

1915–1924

(52, 59)

(224, 239)

(689, 714)

(1671, 1710)

(3205, 3260)

(5155, 5226)

(7675, 7764)

(10502, 10611)

1925–1934

(90, 100)

(326, 344)

(867, 897)

(1764, 1806)

(2983, 3039)

(4259, 4327)

(5730, 5811)

(7285, 7382)

Rate ratio

1895–1904

1905–1914

1.9

2.2

1.8

1.5

1.4

1.2

1.1

1915–1924

5.7

4.3

3.6

2.5

1.7

1.3

1.1

0.9

1925–1934

9.8

6.2

4.5

2.6

1.6

1.1

0.8

0.6

95% CI rate ratio

1895–1904

1905–1914

(1.7, 2.1)

(1.8, 2.0)

(2.1, 2.2)

(1.8, 1.8)

(1.5, 1.5)

(1.3, 1.4)

(1.2, 1.2)

(1.1, 1.1)

1915–1924

(5.3, 6.1)

(4.1, 4.4)

(3.5, 3.7)

(2.5, 2.5)

(1.7, 1.8)

(1.3, 1.3)

(1.1, 1.1)

(0.9, 0.9)

1925–1934

(9.3, 10.3)

(6.0, 6.3)

(4.5, 4.6)

(2.6, 2.7)

(1.6, 1.6)

(1.1, 1.1)

(0.8, 0.8)

(0.6, 0.6)

Women

30–34

35–39

40–44

45–49

50–54

55–59

60–64

65–69

Deaths

1895–1904

264

615

1938

5513

14124

32942

62900

1905–1914

110

317

1006

3082

7750

18683

39662

69061

1915–1924

158

485

1700

4250

9835

20067

37440

59255

1925–1934

233

741

2180

4437

8624

15657

25687

35007

Population (000s)

1895–1904

1739

1709

1669

1648

1607

1554

1480

1366

1905–1914

1773

1750

1710

1670

1640

1595

1516

1394

1915–1924

1756

1752

1722

1702

1665

1609

1534

1430

1925–1934

1541

1539

1527

1503

1466

1419

1359

1270

Mortality rate per 100,000

1895–1904

118

343

909

2226

4603

1905–1914

185

473

1172

2616

4953

1915–1924

250

591

1247

2441

4143

1925–1934

143

295

588

1103

1890

2757

95% CI mortality rate per 100,000

1895–1904

(3, 5)

(14, 17)

(34, 40)

(112, 123)

(334, 352)

(894, 924)

(2203, 2250)

(4568, 4639)

1905–1914

(5, 7)

(16, 20)

(55, 63)

(178, 191)

(462, 483)

(1155, 1188)

(2590, 2641)

(4917, 4989)

1915–1924

(8, 10)

(25, 30)

(94, 103)

(242, 257)

(579, 603)

(1230, 1264)

(2417, 2466)

(4110, 4176)

1925–1934

(13, 17)

(45, 52)

(137, 149)

(287, 304)

(576, 601)

(1086, 1120)

(1868, 1913)

(2729, 2786)

Rate ratio

1895–1904

1905–1914

1.6

1.2

1.6

1.4

1.3

1.2

1.1

1915–1924

2.4

1.8

2.7

2.1

1.7

1.4

1.1

0.9

1925–1934

4.0

3.1

3.9

2.5

1.7

1.2

0.8

0.6

95% CI rate ratio

1895–1904

1905–1914

(1.3, 2.0)

(1.0, 1.3)

(1.5, 1.7)

(1.5, 1.6)

(1.3, 1.4)

(1.3, 1.3)

(1.2, 1.2)

(1.1, 1.1)

1915–1924

(2.0, 2.8)

(1.6, 2.0)

(2.6, 2.8)

(2.1, 2.2)

(1.7, 1.8)

(1.4, 1.4)

(1.1, 1.1)

(0.9, 0.9)

1925–1934

(3.5, 4.5)

(2.9, 3.4)

(3.7, 4.0)

(2.4, 2.6)

(1.7, 1.8)

(1.2, 1.2)

(0.8, 0.9)

(0.6, 0.6)

* Base for rate ratio is the age-stratified mortality rate for the 1895–1904 cohort.

† 95% confidence intervals constructed assuming Poisson distribution of death count variable (Altman, 2000)

In 1945 there were 1,823 and 178 less CHD deaths in the older age group (aged 80 to 84) than in the younger age group (aged 60 to 64) among men and women respectively. Ten years later, in 1955, the older age group among women experienced 1,608 more CHD deaths than the younger age group compared with 2,409 less CHD deaths among men. Another fifty years on in 2005 there were 6,114 and 7,839 more CHD deaths in the older age group among men and women respectively.

The rate of change of CHD mortality rates for each age-sex group is shown in Figures 2 and 3. For younger women (under 50), the rate of change in CHD mortality has reversed in the last 20 years. The line in these charts crossing zero suggests a future plateau and possible reversal of previous improvement in CHD mortality rates. Among younger men, the rate of change in CHD mortality has been more consistent than for women over the past 15 years. The line in these charts remaining below zero indicates that CHD mortality rates in this group have continued to fall steadily. In men aged 45 to 49 and 50 to 54 there appears to be a small reverse in the most recent years included in this series. This pattern is very different within older people where the rate of change in CHD mortality rates has continued to improve over the past 20 years.

Figure 2

Change in CHD mortality rate per 100,000, by age group (35 to 64), men and women, 1931 to 2005

Change in CHD mortality rate per 100,000, by age group (35 to 64), men and women, 1931 to 2005.

Figure 3

Change in CHD mortality rate per 100,000, by age group (65 and older), men and women, 1931 to 2005

Change in CHD mortality rate per 100,000, by age group (65 and older), men and women, 1931 to 2005.

Variations in CHD mortality rates between those birth cohorts with deaths up to age 59 shows that for both men and women the cohort born in 1925 to 1934 experienced higher rates of coronary heart disease than the 1895 to 1904 cohort (Figures 2, 3 and 4). This trend was observed for all ages from 30–34 to 55–59. As an example of one extreme the CHD rate ratio for 1925 – 1934 cohort using the 1895–1904 cohort as a reference shows that among younger men the rate was as much as ten times higher than the earlier cohort (for men aged 30–34) and four times higher for women (aged 30–34). Rate ratios (and 95% confidence intervals) suggest that these comparisons represent significant differences in the rates between the two time periods. Similarly the rate ratio (and 95% CIs) for those aged 60 and over for both men and women are less than 1.0 suggesting that the trend is for lower mortality rates in older birth cohorts. Table 3 presents mortality rates and rate ratios for ten year time periods. Among men in the youngest age groups the rate ratio comparing CHD mortality in recent calendar years with the referent time period (1936–45) shows that CHD mortality rates were consistently higher in all but the oldest male age group. The rate ratios for women suggest that the progress in relative reduction of CHD mortality rates has been more consistent over time.

Table 3

Coronary heart disease deaths, mortality rate, rate ratio and 95% confidence intervals for rate ratios by sex, age and year of death

Men

30–34

35–39

40–44

45–49

50–54

55–59

60–64

65–69

Deaths

1936–45

273

936

2561

5347

10076

15752

21094

23970

1946–55

810

2291

6376

13949

24001

34165

47520

57763

1956–65

1396

4783

10782

21895

41820

65473

83693

92738

1966–75

1576

4946

13834

29887

50471

77214

114210

141632

1976–85

1520

4524

10966

24027

46480

77437

109151

143514

1986–95

1051

3333

8248

16436

28719

49653

81613

119728

1996–2005

810

2332

5550

10987

19740

30404

45011

66886

Mortality rate per 100,000

1936–45

147

226

311

1946–55

163

289

492

736

1956–65

135

268

443

662

1040

1966–75

180

315

522

854

1251

1976–85

167

311

513

789

1257

1986–95

195

374

627

987

1996–2005

111

177

334

577

Rate ratio

1936–45

1.0

1946–55

2.9

2.3

2.0

1.9

2.0

2.2

2.4

1956–65

5.4

4.7

3.4

3.2

3.1

3.0

2.9

3.3

1966–75

6.2

5.5

4.6

4.3

3.6

3.8

4.0

1976–85

5.0

4.1

3.8

3.9

3.6

3.5

4.0

1986–95

3.2

3.0

2.4

2.1

2.2

2.5

2.8

3.2

1996–2005

2.4

1.9

1.5

1.4

1.3

1.2

1.5

1.9

95% CI rate ratio

1936–45

1946–55

(2.7, 3.1)

(2.2, 2.4)

(1.9, 2.0)

(2.0, 2.1)

(1.8, 1.9)

(1.9, 2.0)

(2.2, 2.2)

(2.3, 2.4)

1956–65

(5.1, 5.6)

(4.6, 4.8)

(3.3, 3.4)

(3.1, 3.2)

(3.1, 3.1)

(3.0, 3.0)

(2.9, 2.9)

(3.3, 3.4)

1966–75

(5.9, 6.5)

(5.4, 5.7)

(4.5, 4.7)

(4.2, 4.3)

(3.6, 3.7)

(3.5, 3.6)

(3.8, 3.8)

(4.0, 4.0)

1976–85

(4.8, 5.3)

(4.0, 4.2)

(3.7, 3.9)

(3.9, 4.0)

(3.5, 3.6)

(3.5, 3.5)

(4.0, 4.1)

1986–95

(3.0, 3.4)

(2.9, 3.1)

(2.3, 2.4)

(2.1, 2.2)

(2.2, 2.3)

(2.5, 2.6)

(2.8, 2.8)

(3.2, 3.2)

1996–2005

(2.3, 2.6)

(1.8, 2.0)

(1.4, 1.5)

(1.3, 1.3)

(1.2, 1.2)

(1.5, 1.5)

(1.8, 1.9)

Women

30–34

35–39

40–44

45–49

50–54

55–59

60–64

65–69

Deaths

1936–45

111

267

541

1199

2452

4733

8301

12243

1946–55

133

371

924

2351

4911

9884

19053

31573

1956–65

226

574

1542

3348

7360

15934

30830

50826

1966–75

275

762

2147

4666

9469

18883

39113

67127

1976–85

312

711

1753

3935

9260

20032

37935

65485

1986–95

247

575

1349

2730

5744

13102

29180

55030

1996–2005

190