Jump to: Page Content, Site Navigation, Site Search,
You are seeing this message because your web browser does not support basic web standards. Find out more about why this message is appearing and what you can do to make your experience on this site better.
D A Lawlor Department of Social Medicine,
University of Bristol, Bristol BS8 2PR Correspondence to: D A Lawlor D.A.Lawlor{at}bristol.ac.uk
| |
Abstract |
|---|
|
|
|---|
Objective:
To examine secular trends and geographical variations in sex differences in mortality from coronary heart disease
and investigate how these relate to distributions in risk factors.
Design:
National and international data were
used to examine secular trends and geographical variations in sex
differences in mortality from coronary heart disease and risk factors.
Setting:
England and Wales, 1921-98; Australia,
France, Japan, Sweden, and the United States, 1947-97; 50 countries,
1992-6.
Data sources:
Office for National Statistics, World
Health Organization, and Food and Agriculture Organization of the
United Nations.
Results:
The 20th century epidemic of coronary heart disease affected only men in most industrialised countries and had a
very rapid onset in England and Wales, which has been examined in
detail. If this male only epidemic had not occurred there would have
been 1.2 million fewer deaths from coronary heart disease in men in
England and Wales over the past 50 years. Secular trends in mean per
capita fat consumption show a similar pattern to secular trends in
coronary heart disease mortality in men. Fat consumption is positively
correlated with coronary heart disease mortality in men
(rs=0.79; 95% confidence interval 0.70 to
0.86) and inversely associated with coronary heart disease mortality in
women (
0.30;
0.49 to
0.08) over this time. Although sex ratios
for mortality from coronary heart disease show a clear period effect,
those for lung cancer show a cohort effect. Sex ratios for stroke
mortality were constant and close to unity for the entire period.
Geographical variations in the sex ratio for coronary heart disease
were associated with mean per capita fat consumption (0.64; 0.44 to
0.78) but were not associated with the sex ratio for smoking.
Conclusion:
Sex differences are largely the result of environmental factors and hence not inevitable. Understanding the
factors that determine sex differences has important implications for
public health, particularly for countries and parts of countries where
the death rates for coronary heart disease are currently increasing.
|
What is already known on this topic
What this study adds
|
| |
Introduction |
|---|
|
|
|---|
It is well known that there is a sex difference in mortality from coronary heart disease; the reason for this difference is widely assumed to be due to the protective effect of oestrogen. However, trials in the 1960s and 1970s to prevent coronary heart disease in men by giving them high doses of oestrogen had unfavourable results.1 If environmental factors play a part in the sex difference in the occurrence of coronary heart disease then it may be possible to reduce mortality in men to levels similar to those found in women.
Few studies have looked at secular trends in the sex difference in
mortality in coronary heart disease despite the obvious potential for
such analyses to provide valuable insights into this phenomenon. In
this study we examine secular and geographical trends in the sex ratio
for coronary heart disease mortality and other related conditions and
compare these to trends in distributions in risk factors.
| |
Methods |
|---|
|
|
|---|
Secular trends
We used Office for National Statistics data to examine secular
trends from 1921-98 in mortality for coronary heart disease and other
conditions that coronary heart disease may have been misdiagnosed
as
stroke, other circulatory disease, renal disease, respiratory
disease, and ill-defined mortality
in men and women aged 34 to 75, in
England and Wales. In addition, we assessed secular trends in sex
ratios for mortality from lung cancer from 1940, when lung cancer was
first included in International Classification of Diseases (ICD) codes.
Total mean per capita proportion of energy derived from fat and total
mean per capita alcohol consumption for the United Kingdom over the
period 1921-97 were obtained from published
sources.2-5
Geographical variations
We used WHO data to calculate the sex ratio of mortality from
coronary heart disease and lung cancer using age standardised five year
aggregate death rates (1992-6) for 50 countries. For each country we
calculated a five year aggregate (1992-6) mean daily per capita total
energy derived from fat using data from the Food and Agriculture
Organization (FAO) of the United Nations.6 Sex specific
smoking prevalence for a single year only (1990) and for European
countries only was obtained from the WHO.
Accuracy and completeness of mortality data
Between 95% and 100% of the deaths for all of the data examined
in this study had been certified. In addition, for all countries over
all time periods the proportion of deaths attributed to the diagnostic
category "signs and symptoms and other ill defined conditions" was
less than 5% and did not differ between the sexes. The only exception
was Brazil, where over 16% of deaths were for ill defined conditions.
However, this did not vary between men and women, and excluding data
from Brazil from the analyses did not affect any of the outcomes.
Statistical analysis
All rates were age standardised by the direct method weighted to
the WHO European standard population. Regression modelling was used to
determine the year in which there was a significant change in observed
trends.7 Spearman's rank correlation coefficient
(rs) was used to assess associations
between sex ratios and risk factor distributions. All analyses used
Stata version 6.0.
|
| |
Results |
|---|
|
|
|---|
Secular trends
From 1921 to 1949, in England and Wales, coronary heart disease
mortality was higher in men than in women but the pattern of change was
similar in both. From 1949 the trends diverged, with a marked increase
in men, peaking in the early 1970s. Rates in women over the same time
period were stable or declined (fig 1). These changes resulted in an
increase in the sex ratio from a constant value of 1.5 between 1921 and
1949 to a peak of 3.5 in 1972 (fig 2). This change began in the same
year (1949) in all age groups (fig 3). If the sex ratio had remained at
1.5 and rates for women stayed as they were for the whole period, 1.2 million fewer deaths would have occurred in men between 1949 and 1998.
|
|
0.30,
0.49 to
0.06, P=0.01). The
calculations incorporating the assumption that there is a 10 year lag
in the effect of dietary fat on coronary heart disease9 slightly strengthen the correlation between fat consumption and the sex
ratio in coronary heart disease mortality to 0.96 (0.94 to 0.98, P<0.01).
Mean per capita alcohol consumption was correlated with the sex ratio
in mortality from coronary heart disease over this period (0.51, 0.32 to 0.66, P<0.01); it was weakly positively correlated with male
mortality from coronary heart disease and inversely correlated with
female mortality from coronary heart disease (0.25, 0.03 to 0.45, P=0.04;
0.49,
0.64 to
0.30, P<0.01, respectively).
For lung cancer the sex ratio showed a clear cohort effect, with the
peak occurring in later years for each successively older cohort (fig
4). Death rates for stroke decreased in both men and women over the
entire period with the sex ratio remaining around unity for the period.
There was no corresponding increase in death rates in women or decrease
in the sex ratios for any of the diagnostic categories to which
misdiagnosed coronary heart disease deaths could possibly have been
assigned.
|
|
Geographical trends
Across the 50 countries considered, the sex ratio for mortality
from coronary heart disease ranged from 1.4 to 2.9 (table). The highest
ratios were seen in Poland, France, and Norway and the lowest in rural
China, Cuba, and Armenia. The sex ratio for mortality from coronary
heart disease was positively associated with mean per capita fat
consumption (0.64, 0.44 to 0.78, P<0.01) but was not associated with
either the sex ratio for lung cancer mortality or the sex ratio for
smoking prevalence. The sex ratio for lung cancer was associated with
the sex ratio for smoking prevalence (0.49, 0.09 to 0.67, P=0.01).
|
| |
Discussion |
|---|
|
|
|---|
The sex difference in mortality from coronary heart disease varies
over time and geographically
the 20th century epidemic of coronary
heart disease affected only men in England and Wales and other
industrialised countries. A protective effect of oestrogen alone cannot
explain these trends because it is inconceivable that levels of
oestrogen in women have changed dramatically over the past century or
vary greatly among women of different countries. Indeed, the dramatic
"period effect" seen in the secular trends in the sex ratio for
mortality from coronary heart disease suggests an environmental impact
that affects only men and occurred before the late 1940s.
Artifact as a possible explanation
Secular trends may be affected by changes in coding practice,
diagnostic fashion, and increased survival of the
population.10 Changes in coding practice and increased survival should affect men and women in the same way and would therefore not explain changes in the sex ratio. Our data show that
trends in male and female mortality from coronary heart disease mirrored each other between 1921 and 1949, during which time there were
three ICD changes. We could find no compensatory change in death rates
in any other causes of death to which women with coronary heart disease
could plausibly be misdiagnosed. The population denominators used in
this study have changed over time. In particular, during both world
wars the populations referred to civilian populations only and had a
lower proportion of healthy individuals.11 The changes in
population denominators for the war period affected both sexes in the
same way and therefore cannot explain the sex differences in secular
trends.11 By using death rates that were age standardised
we have adjusted for the changing age distribution of the population.
that is, in the
1920s.
14 15
None of these studies attempt to explain why
the risk of heart disease mortality in men should have increased over
time and differently between places.
Sex differences in effect or distribution of known risk factors
The level of risk for smoking, hypertension, and cholesterol
the
major risk factors for coronary heart disease
is the same for men and
women.16 Changes in sex differences in smoking behaviour
in the United States over the past 30 years predict secular trends in
sex differences in lung cancer; they do not predict changes in sex
differences for coronary heart disease.17 Our analyses
over a longer period concur with these results. The secular trends in
the coronary heart disease sex ratio suggest an exposure with a
differential impact affecting all generations at the same time
that
is, a period effect. This contrasts with the pattern for lung cancer,
where the cohort effect suggests effects influencing successive
generations throughout their lives
the uptake of smoking is the
obvious exposure. If the observed trends for sex ratio for coronary
heart disease were due to sex differences in smoking distribution we
would expect to find a cohort relationship similar to that seen for
lung cancer, which is undeniably caused by smoking. Furthermore,
geographical variation in sex ratios for coronary heart disease is not
associated with sex ratios in prevalence of lung cancer or smoking.
Although it is abundantly clear that cigarette smoking is an important
determinant of male or female individual susceptibility to coronary
heart disease, our findings show that a sex difference in smoking rates
is not the explanation for the sex difference in coronary heart
disease. Sex differences in hypertension over time or between countries cannot explain the sex differences in coronary heart disease as there
are no sex differences in stroke mortality, which is clearly influenced
by hypertension. Age adjusted mean cholesterol concentrations do not
differ between men and women in the WHO MONICA (monitoring trends and
determinants in cardiovascular disease) study centres18 and in the United States have not differed over time between the sexes
since the 1960s.19
Alcohol consumption
The relation between mean alcohol consumption and coronary heart
disease risk is J shaped in both men and women and there is evidence
that drinking pattern is also important in coronary heart disease, with
binge drinking being harmful.20 It is possible that our
secular trend results reflect different drinking patterns between men
and women, with mean per capita increases reflecting an increase of
binge drinking in men. This is unlikely, however, as there was no
similar change in the sex difference in stroke mortality over this period.
Food consumption
Both secular and geographical trends in the sex ratio are strongly
correlated to total mean per capita fat consumption. This implies
either that dietary fat intake differs between men and women or that
women and men differ in their response to dietary fat. A differential
response between men and women to dietary fat has been suggested.
Evidence from randomised controlled trials shows that the concentration
of high density lipoprotein cholesterol is increased in women more
readily than in men in response to diets high in saturated fat, and it
is reduced with low fat diets to a greater extent in women than
men.
21 22
Recent studies have shown that atherogenic
lipid profiles are associated with increased risk of ischaemic, but not
haemorrhagic, strokes.23 A change over time in the sex
difference in ischaemic stroke mortality may not be discernible in our
study, which, when routine data are used, is unable to distinguish
between types of strokes. Further studies are required to assess
whether there is indeed a differential response to dietary fat between
women and men.
War as an explanation for these trends
Feinleib suggested that because the male epidemic in
coronary heart disease began in the 1920s in the United States, factors
associated with the first world war may have been responsible for the
increased mortality from coronary heart disease in men.15 In our data for the United Kingdom, the divergence begins shortly after
the second world war. Large numbers of the fittest men may have been
lost in conflict, with the result that rates of coronary heart disease
were higher in the less fit men who remained. Although there is no
direct evidence that war leads to greater depression in men than women,
it has been shown that depression is associated with an increased risk
of coronary heart disease.28 War is an unlikely
explanation for the secular trends because mortality from coronary
heart disease in men continued to increase in both the United States
and the United Kingdom for over 20 years after the end of the conflicts
and increased in men of all ages. Conflict cannot explain geographic
variations in the sex difference of mortality from coronary heart disease.
Conclusion
Secular and geographical trends indicate that a protective
effect of endogenous oestrogen does not explain the sex difference in
occurrence of coronary heart disease and that environmental factors are
important. Identification of the factors responsible for sex
differences in occurrence of coronary heart disease could importantly
inform preventive strategies, particularly in countries or parts of
countries where rates of coronary heart disease are currently increasing.
| |
Acknowledgments |
|---|
Contributors: All authors designed the study and formulated the hypotheses. DAL retrieved data, undertook the analysis, and wrote the initial draft of the paper. All authors contributed to the final paper and all act as guarantors.
| |
Footnotes |
|---|
Funding: None.
Competing interests: None declared.
Full details of all data sources
and ICD codes are provided on the BMJ's website
| |
References |
|---|
|
|
|---|
| 1. |
Coronary Drug Project Research Group.
The coronary drug project. Findings leading to discontinuation of the 2.5-mg day estrogen group.
JAMA
1973;
226:
652-657 |
| 2. | Stephen AM, Sieber GM. Trends in individual fat consumption in the UK 1900-1985. Br J Nutr 1994; 71: 775-788[CrossRef][Medline]. |
| 3. | Petersen S, Mockford C, Rayner M. Coronary heart disease statistics. British Heart Foundation statistics database 1999. London: British Heart Foundation, 1999. |
| 4. | Advisory Panel on Diet in relation to Cardiovascular and Cerebrovascular Disease. Diet and coronary heart disease. London: HMSO, 1974. |
| 5. | Plant M. Trends in alcohol and illicit drug-related diseases. In: Charlton J, Murphy M, eds. The health of adult Britain 1841-1994. London: Stationery Office, 1997:114-127. |
| 6. |
Sasaki S, Kesteloot H.
Value of Food and Agriculture Organization data on food-balance sheets as a data source for dietary fat intake in epidemiologic studies.
Am J Clin Nutr
1992;
56:
716-723 |
| 7. | Kim HJ, Fay MP, Feuer EJ, Midthune DN. Permutation tests for joinpoint regression with applications to cancer rates. Stat Med 2000; 19: 335-351[CrossRef][Medline]. |
| 8. | Charlton J, Murphy M. The health of adult Britain 1841-1994. London: Stationery Office, 1997. |
| 9. | Stamler J. Opportunities and pitfalls in international comparisons related to patterns, trends and determinants of CHD mortality. Int J Epidemiol 1989; 18: S3-18[Abstract]. |
| 10. | Stehbens WE. An appraisal of the epidemic rise of coronary heart disease and its decline. Lancet 1987; i: 606-611. |
| 11. | Charlton J. Trends in all cause mortality: 1841-1994. In: Charlton J, Murphy M, eds. The health of adult Britain: 1841-1994. London: Stationery Office, 1997:17-29. |
| 12. |
Zhang XH, Sasaki S, Kesteloot H.
The sex ratio of mortality and its secular trends.
Int J Epidemiol
1995;
24:
720-729 |
| 13. | Uemura K, Pisa Z. Trends in cardiovascular disease mortality in industrialized countries since 1950. World Health Stat Q 1988; 41: 155-178[Medline]. |
| 14. |
Anderson TW.
Mortality from ischemic heart disease. Changes in middle-aged men since 1900.
JAMA
1973;
224:
336-338 |
| 15. | Feinleib M. Trends in heart disease in the United States. Am J Med Sci 1995; 310(suppl 1): S8-14. |
| 16. | Isles CG, Hole DJ, Hawthorne VM, Lever AF. Relation between coronary risk and coronary mortality in women of the Renfrew and Paisley survey: comparison with men. Lancet 1992; 339: 702-706[CrossRef][Medline]. |
| 17. | Waldron I. Recent trends in sex mortality ratios for adults in developed countries. Soc Sci Med 1993; 36: 451-462. |
| 18. | Kuulasmaa K, Tunstall-Pedoe H, Dobson A, Fortmann S, Sans S, Tolonen H, et al. Estimation of contribution of changes in classic risk factors to trends in coronary-event rates across the WHO MONICA project populations. Lancet 2000; 355: 675-687[CrossRef][Medline]. |
| 19. | Posner BM, Franz MM, Quatromoni PA, Gagnon DR, Sytkowski PA, D'Agostino RB, et al. Secular trends in diet and risk factors for cardiovascular disease: the Framingham Study. J Am Diet Assoc 1995; 95: 171-179[CrossRef][Medline]. |
| 20. |
Britton A, McKee M.
The relation between alcohol and cardiovascular disease in Eastern Europe: explaining the paradox.
J Epidemiol Community Health
2000;
54:
328-332 |
| 21. |
Clifton PM, Nestel PJ.
Influence of gender, body mass index, and age on response of plasma lipids to dietary fat plus cholesterol.
Arterioscler Thromb
1992;
12:
955-962 |
| 22. |
Walden CE, Retzlaff BM, Buck BL, McCann BS, Knopp RH.
Lipoprotein lipid response to the national cholesterol education program step II diet by hypercholesterolemic and combined hyperlipidemic women and men.
Arterioscler Thromb Vasc Biol
1997;
17:
375-382 |
| 23. |
Hart CL, Hole DJ, Smith GD.
The relation between cholesterol and haemorrhagic or ischaemic stroke in the Renfrew/Paisley study.
J Epidemiol Community Health
2000;
54:
874-875 |
| 24. |
Stephen AM, Wald NJ.
Trends in individual consumption of dietary fat in the United States, 1920-1984.
Am J Clin Nutr
1990;
52:
457-469 |
| 25. | Cooper S. Snoek piquante. The trials and tribulations of the British housewife. In: Siaaons M, French P, eds. Age of austerity 1945-51. Oxford: Oxford University Press, 1986:34-57. |
| 26. | Charles N, Kerr M. Women, food and families. Manchester: Manchester University Press, 1997. |
| 27. | Oren L. The welfare of women in labouring families: England, 1860-1950. In: Hartman MS, Banner L, eds. Clio's consciousness raised: new perspectives on the history of women. London: Harper and Row, 1974:226-244. |
| 28. |
Hemingway H, Marmot M.
Evidence based cardiology: psychosocial factors in the aetiology and prognosis of coronary heart disease. Systematic review of prospective cohort studies.
BMJ
1999;
318:
1460-1467 |
(Accepted 17 May 2001)
Read all Rapid Responses