Social Inequality, Psychosocial Factors and CHD:
What Have We Learned
from the Research in Rich Countries?
John Lynch
Department of Epidemiology, Biostatistics and Occupational Health
McGill University, Montreal, Canada
PURE - Dubai, January 2006
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SocialAdvantage
The Social Gradient in CHD
SocialDisadvantage
What have we learned from social epidemiology?
The First Whitehall Study
0
1
2
3
4
5
Administrative Professional Clerical Other
RR
Rose and Marmot. Br Heart J (1981)
2.1
3.2
4.0*Adjust for smoking, blood pressure, cholesterol, overweight etc
1.8
2.3
2.6
35%
“The social class difference was partly explained by known
coronary risk factors: men in the lower grades smoked more
and exercised less, they were shorter and more overweight,
and they had higher blood pressures and lower levels of
glucose tolerance. Most of the difference, however, remains
unexplained. It seems that there are major risk factors yet to
be identified, …”
Rose and Marmot (1981, p.13)
“… if these aspects of lifestyle account for less than a third of the social gradient in
mortality, what accounts for the other two thirds? The second question occupies the
rest of this book.” (p. 45 of 320) Marmot (2004)
1. There must be other mechanisms at the individual and contextual level that
generate social gradients in CHD such as stress, job control, autonomy,
social participation, neighborhood effects, social capital, etc.
i.e., a range of psychosocial factors
Implications (1)
Type A Behavior Pattern
Cynical Distrust
Anger/Anger-in/Anger-out/
Hostility
Social Isolation
Social Support
Control
Sense of Control
Mastery
Hopelessness
Depression
Stress
Sense of Coherence
Hardiness
Optimism
John Henryism
Job Strain
Ways of Coping
Anxiety
Self esteem
Resilience
Social cohesion
Social capital
Psychosocial factors in social epidemiology
CHD
2. Interventions focused on health behaviors and conventional risk factors are unlikely
to appreciably reduce the social gradient in health.
For instance, a 1998 JAMA study that has been cited more than 200 times (Web of
Science), stated that, “Thus, public health policies and interventions that exclusively
focus on individual risk behaviors have limited potential for reducing socioeconomic
disparities in mortality.” (p. 1707)
Implications (2)
Behaviours do not matter
Behaviours matter but they are just not the “big story”
The downplaying of behaviours and their physiological correlates
in understanding social inequalities in CHD
influences research, funding, interventions and policy.
Social Inequality
CHD
Traditional RiskFactors
P-N-E Immune Function
ControlDepression
Stress
behaviours
INTERHEART: PAR ~ 75%
• Conventional risk factors – smoking, hypertension, dyslipidemia and diabetes do explain
most CHD in populations
• INTERHEART study (2004) show PAR for 4 conventional risk factors is 76%
• Emberson, Whincup, et al (2005) in BRHS show smoking, blood pressure and cholesterol
account for 81% PAR (adjusted for regression dilution bias)
• Stamler (1992,1999) and Greenland (2003) show that 75-100% of all CHD cases occur
among those exposed to at least one conventional risk factor
What have we learned from CHD epidemiology?
So how can it be that the factors accounting for most CHD in a population
do not seem to account for most of the social gradient in CHD, when the
social gradient simply emerges from sub-grouping the population
according to some indicator of social position?
A Paradox?
1000 cases of CHD
Least educated
600
Middle educated
300
Most educated
100
0
100
200
300
400
500
600
700
LeastEducated
MostEducated
Lipids, hypertension, smoking, diabetes
A Paradox?
• Population sample of 2,682 Finnish men – Kuopio IHD Study
• Stratified the population into lower and higher risk groups based on standard clinical
definitions - current smoking, hypertension, dyslipidemia and prevalent diabetes
• 34.7% were current smokers, 58.7% had hypertension, 42.7% had dyslipidemia, 6.5%
had diabetes, and 84.9% had at least one of these risk factors
• Fatal (ICD9 codes 410-414) and nonfatal CHD, classified according to MONICA criteriia
• There were 425 CHD events (108 fatal, 317 non-fatal) during an average follow-up of
10.5 years.
An Illustration
Lynch, Davey Smith, Harper, Bainbridge. J Epidemiol Community Health (in press)
• Of the 425 total cases - 402 (94.6%) occurred among men exposed to at least one of
the four conventional risk factors
• 70%+ of cases occurred in men with at least 2 risk factors
• PAR ~ 70%
• Similar to INTERHEART (PAR ~ 75%) and with US cohorts where 90%+ of cases occur
among those exposed to at least one conventional risk factor
Thus these results are consistent with the idea that
conventional risk factors DO EXPLAIN the vast majority of CHD cases
Accounting for Cases of CHD in this Population
• Social gradient in CHD comparing high to low education is RR = 1.90
• After adjustment for conventional risk factors RR = 1.68
• This corresponds to a 24% reduction in the excess RR
Thus these results are consistent with the idea that
conventional risk factors DO NOT EXPLAIN the social gradient in CHD
Accounting for the Social Gradient in CHD in this Population
What would population levels and social gradients in CHD look like
if there were no conventional risk factors in this population?
N(%)
No. of Cases (%)
Risk(per K)
RR Risk
ER (per K)
Education
< Primary school
1,121(41.8)
218 (51.3)
194 1.83 88
Some high school
1,128(42.1)
161(37.9)
143 1.35 37
High school
graduate
433(16.1)
46(10.8)
106 1.0 0
Total 2,682 425 158 - -
N(%)
No. of Cases (%)
Risk(per K)
RR Risk
ER (per K)
Education
< Primary school
122 (30.2)
8 (34.8)
66 1.63 25
Some high school
184 (45.5)
11(47.8)
60 1.46 19
High school
graduate
98 (24.3)
4(17.4)
41 1.0 0
Total 404 23 57 - -
Whole KIHD PopulationN = 2,682
Low Risk Segment of KIHD PopulationN = 404 (15.1%)
0
50
100
150
200
250
Least Educated Most Educated
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66 6041
Excess Risk (whole pop) = 88 per 1000Excess Risk (“low risk” pop) = 25 per 1000
Make it a low risk pop = 72% reduction in the excess risk of social inequality in CHD194
143
106
Low risk population
Low risk population
Low risk population
RR = 1.8
RR = 1.6
In a low risk population with no smoking, hypertension, dyslipidemia and
diabetes
• Relative social gradient in CHD remains
RR = 1.8whole vs 1.6low risk
• Absolute social gradient is reduced by 72%
ER = 88whole vs 25low risk per 1,000
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Social Disadvantage
Original social inequality in CHD
Give the disadvantaged the same risk factor levels as the most advantaged
If we intervened to substantially reduce risk factors in all social groups
Which social inequality is “better”?
Social Advantage
• Within an absolute risk framework, there is no paradox between the observations from
CHD and social epidemiology. Conventional risk factors do account for most CHD and for
most of the absolute social gradient in CHD (72% of the excess risk).
• However, when explaining relative social gradients in CHD, the apparent paradox may
arise that the factors which explain most cases of CHD do not explain the relative social
gradient.
• Adjustment for conventional risk factors only reduced the relative social gradient in CHD by
24%. This is normally interpreted to mean that most of the effects of social inequality on
CHD do not work through mechanisms linked to conventional risk factors.
• The extent to which a 3rd variable reduces the RR in an exposure-outcome association
(an indication of confounding of the association) depends on the relative distributions of
the exposure over strata of the 3rd variable and the strength of its association with the
outcome.
• In this case there is a more extreme relative distribution of education over strata of
hopelessness than over strata of the conventional risk factors (partly because the
prevalence of conventional risk factors is high), and so hopelessness/depression appears
to be a stronger confounder (in this case interpreted as a mechanism) of the association
between education and CHD.
What does it take to be a confounder?
Education
CHD
Depression
Conventional Risk Factors
28%
24%
SocialGradient RR=1.9
on the basis of the adjusted RR analysis we would normally interpret hopelessness/depression
as an important mechanism in the causation of the social gradient in CHD
• intervene to eliminate hopelessness / depression
reduces the relative social gradient 28%
eliminates 14% of CHD cases (confounded estimate)
• intervene to eliminate smoking, hypertension, dyslipidemia and diabetes
smaller reduction in the relative social gradient – 24%
eliminate 90%+ of CHD cases and 72% of the absolute social gradient
How important are these 2 mechanisms?
• 72% reduction in ER is an underestimate because “low risk” population
is not really low risk
• No differences in blood pressure and have higher BMI
• but low risk population has ex-smokers, higher cholesterol and LDL,
and are 5 cm shorter
• Deciding on the “importance” of various risk factors for elucidating the mechanisms
behind social gradients in CHD cannot be done on the basis of relative comparisons
alone.
• As Geoffrey Rose commented:
“Relative risk is not what decision-taking requires … relative risk is only for researchers;
decisions call for absolute measures.”
p. 19, Strategy of
Preventive Medicine.
0
50
100
150
200
250
300
350
400
1900 1910 1920 1930 1940 1950 1960 1970 1980 1990
Infant M
ortalit
y per
1,000
0
0.5
1
1.5
2
2.5
3
Relati
ve Dis
parity
Black – White Inequality in Infant Mortality
over the 20th Century, USA
Relative Inequality
White
Black
0
50
100
150
200
250
300
350
400
1900 1910 1920 1930 1940 1950 1960 1970 1980 1990
Infant M
ortality
per 1,0
00
0.0
20.0
40.0
60.0
80.0
100.0
120.0
140.0
160.0
180.0
200.0
Absolut
e Dispa
rity
Absolute Inequality
White
Black
0
20
40
60
80
100
1
3
5
7
9
RR
Age-specific Mortality Differences between the
Richest and Poorest 20% of the World’s Population
Gwatkin (2000)
Poorest 20%
Richest 20%
Mo
rtal
ity
Rat
e p
er 1
000
RR
• Explaining and reducing relative social gradients in CHD is a legitimate and important
focus of research and intervention because it can help reveal novel CHD risk factors and
mechanisms that are unevenly distributed across social groups.
• However, explanations for relative social gradients need to be understood within the
context of what causes most cases of CHD. Otherwise they may deflect attention from
the most important population-level causes.
• Rose – if everyone in the population smoked we would be finding that radon or
asbestos were the most important causes of lung cancer
• In populations where the prevalence of conventional risk factors is high, it is possible that
there are no or small social gradients in those risk factors such that they cannot account
for relative CHD differences across social groups but contribute substantially to the
absolute risk of CHD in all social groups.
• In the Whitehall Study there are small social differences in blood pressure and no social
differences in total cholesterol
• So reducing major, high prevalence risk factors from the population may have little effect
on the relative social gradient but a large effect on the absolute social gradient as
indicated by a reduction in the excess risk.
• Importantly, this also means that whatever proximal (CRP) and distal factors (social
capital) are identified as causes of the relative social gradient in CHD, if their behavioral
and biological mechanisms do not involve conventional risk factors then they probably
account for a small proportion of CHD cases.
Social Inequality
CHD
Traditional RiskFactors
P-N-E Immune Function
ControlDepression
Stressbehaviours
INTERHEART: PAR ~ 80%
?
200
300
400
500
600
700
1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
rate
pe
r 1
00
,00
0
10
20
30
40
50
60
70
80
gin
i co
eff
icie
nt/
po
vert
y
heart disease
income inequality
Income Inequality, Poverty and Heart Disease: 1900-2000, USA
poverty
700.00
800.00
900.00
1,000.00
1,100.00
1,200.00
1,300.00
1,400.00
1,500.00
1,600.00
1,700.00
1968 1970 1972 1974 1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998
40.0
45.0
50.0
55.0
60.0
65.0
70.0
Race-specific Voting Participation in Presidential Elections and age-adjusted, all-cause mortality, USA, 1968 - 1998
Year
All-
cau
se m
orta
lity
per
100
,000
% V
oting in Pre
sidential elections
Black Mortality
White Mortality
Black Voting
White Voting
Lynch and Davey Smith (2003)
0
100
200
300
400
500
600
700
800
1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
0
500
1000
1500
2000
2500
3000
AA
DR
Per C
apita Consum
ptionSex-Specific Smoking Trends and Heart Disease, 1900-1998, USA
Male Heart Disease
Female Heart DiseaseMale Smoking
Female Smoking
0
10
20
30
40
50
60
70
80
90
100
1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000
0
500
1000
1500
2000
2500
3000
Gin
iP
er Capita C
onsumption
Sex-Specific Smoking Trends and Income Inequality, 1900-1998, USA
Male Smoking
Female Smoking
Income Inequality
37
38
39
40
41
42
43
44
45
46
47
1980 1985 1990 1995 2000
4.9
5
5.1
5.2
5.3
5.4
5.5
5.6
Sex-Specific Cholesterol Trends and Income Inequality, 1980-2002, USA
Total Cholesterol Trends from Minnesota Heart Survey: Arnett et al. Circulation (2005)
Gini
Male Cholesterol
Female Cholesterol
• We should re-affirm that smoking, hypertension, dyslipidemia and diabetes are the most
important causes of CHD in populations and of social gradients in CHD.
• If our concern is to reduce the overall population health burden of CHD and the
population health burden of CHD inequalities, then reducing conventional risk factors will
do the job.
• Eliminating the social gradient in CHD attributable to non-traditional risk factor
mechanisms will make a modest contribution to improving overall population health
because the magnitude of the between social group CHD differences is small relative to
the total risk variation in the population and to that due to traditional risk factors.
Conclusion
We should increase our efforts to find ways to influence the multiple pathways
from international, national and local policy through to individual behaviour that will
reduce conventional risk factors among current and future generations in richer
and poorer countries.
Conclusion
Individual and Population Level Causation
Issues for PURE
0
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500
600
700
“Heart Disease”
All Stroke
RiskFactors
SEP
INTERHEART
Psychosocial – CHD
PAR ~ 30%Psychosocial
CHD
Stress
SEP
?
CHD
Black Africans Coloured White
SEP Steyn, et al Circulation (2005)
Social Inequality
Major RiskFactors
PsychosocialFactors
CHD
PURE
Social, economic, demographic, behavioural transition
ReportingTendency
Thank you
Triangulating Epidemiology
Populations
Sub-groups
Individuals
Biology
Genetics
Disease
Disease Trends
Populations
Sub-groups
Individuals
Biology
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1) Original population levels and social inequality in CHD
2) Social inequality and levels of CHD after reduction in social inequality and/or psychosocial causes?
3) Social inequality and levels of CHD after population-wide reductions in risk factors?
Which social inequality is “better”?
SocialAdvantage
SocialDisadvantage
• in terms of CHD and probably many other diseases as well, we should focus
on the developmental influences (political, economic, social, psychological,
biological, genetic) on population levels and social inequalities in the major
health behaviors in rich and poor countries
Implications for Research on Human Growth and Development
Important to reiterate Geoffrey Rose
• The causes of individual cases of CHD.
The positive predictive value for individual risk prediction is very low because lots of
people with conventional risk factors don’t get CHD
– what makes people susceptible to the risk factors?
Vs
Current or Former Smoker
CHD (fatal or non-fatal) Lung Cancer Death
172 / 1000 15 / 1000
Never Smoker 12 / 1000 0
Risk of CHD and Lung Cancer by Smoking Status
Vs
• The causes of population levels of CHD
Almost all cases of CHD do have the conventional risk factors and so population levels almost completely accounted for 3-4 conventional risk factors
Thus eliminating the risk factors eliminates the disease
“If causes can be removed, then susceptibility ceases to matter”
Geoffrey Rose
Extensions
1. Understand why a relative social gradient (RR=1.6) remains even in a low risk population
2. Given the differential distribution of exposure to at least 1 risk factor across educational
groups, is the exposure distribution enough to account for the greater disease burden
generated among the low educated?
Greater exposure or greater susceptibility?
% exposed to 1+ CHD Risk per 1,000
High ed. 77 65
Mid ed. 84 83
Low ed. 89 128
15% 97%
(1997)