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
What have we learned from social epidemiology?
CHD Rate / 100K
The Social Gradient in CHD
Social
Disadvantage
Social
Advantage
The First Whitehall Study
5
4
*Adjust for smoking, blood pressure, cholesterol, overweight etc
4.0
RR
3.2
3
2.6
2.1
2
2.3
35%
Clerical
Other
1.8
1
0
Administrative
Professional
Rose and Marmot. Br Heart J (1981)
“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)
Implications (1)
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
Psychosocial factors in social epidemiology
Type A Behavior Pattern
Stress
Cynical Distrust
Sense of Coherence
Anger/Anger-in/Anger-out/
Hardiness
Hostility
Optimism
Social Isolation
John Henryism
Social Support
Job Strain
Control
Ways of Coping
Sense of Control
Anxiety
Mastery
Self esteem
Hopelessness
Resilience
Depression
Social cohesion
Social capital

CHD
Implications (2)
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)
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
Control
Depression
Stress
behaviours
P-N-E
Immune Function
Traditional Risk
Factors
INTERHEART: PAR ~ 75%
CHD
What have we learned from CHD epidemiology?
• 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
A Paradox?
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?
Lipids, hypertension,
smoking, diabetes

1000 cases of CHD

Most
educated
100
Middle
educated
300
Least
educated
600
700
600
500
400
300
200
100
0
Le a s t
E duc a t e d
M o st
E duc a t e d
An Illustration
• 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.
Lynch, Davey Smith, Harper, Bainbridge. J Epidemiol Community Health (in press)
Accounting for Cases of CHD in this Population
• 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 the Social Gradient in 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
What would population levels and social gradients in CHD look like
if there were no conventional risk factors in this population?
Whole KIHD Population
N = 2,682
N
(%)
Low Risk Segment of KIHD Population
N = 404 (15.1%)
No. of Risk RR
Cases (per Risk
(%)
K)
N
(%)
ER
(per
K)
No. of Risk RR
Cases (per Risk
(%)
K)
ER
(per
K)
Education
Education
1,121 218
(41.8) (51.3)
194
1.83
88
< Primary 122
8
school
(30.2) (34.8)
66
1.63
25
Some high 1,128 161
school
(42.1) (37.9)
143
1.35
37
Some high 184
11
school
(45.5) (47.8)
60
1.46
19
433
46
(16.1) (10.8)
106
1.0
0
High
school
graduate
41
1.0
0
2,682
158
-
-
Total
57
-
-
< Primary
school
High
school
graduate
Total
425
98
4
(24.3) (17.4)
404
23
250
Excess Risk (whole pop)
Excess Risk (“low risk” pop)
CHD Risk / 1000
200
150
194
RR = 1.8
= 88 per 1000
= 25 per 1000
Make it a low risk pop = 72% reduction in
the excess risk of social inequality in CHD
143
100
50
0
106
66
RR = 1.6
60
Low risk
population
Low risk
population
Least Educated
41
Low risk
population
Most Educated
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
Which social inequality is “better”?
Original social inequality in CHD
CHD Rate / 100K
Give the disadvantaged the same
risk factor levels as the most
advantaged
If we intervened to substantially
reduce risk factors in all social
groups
Social Disadvantage
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.
What does it take to be a confounder?
• 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.
Depression
Education
 28%
Social
Gradient
RR=1.9
 24%
Conventional
Risk Factors
CHD
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
How important are these 2 mechanisms?
• 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
• 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.
Black – White Inequality in Infant Mortality
3
Relative
Inequality
300
2
250
200
150
2.5
1.5
Black
1
100
50
White
0
1900 1910 1920 1930 1940 1950 1960 1970 1980 1990
0.5
0
Infant Mortality per 1,000
Infant Mortality per 1,000
350
400
Relative Disparity
400
200.0
180.0
160.0
140.0
120.0
350
300
250
200
Black
150
100
50
White
Absolute
Inequality
0
1900 1910 1920 1930 1940 1950 1960 1970 1980 1990
100.0
80.0
60.0
40.0
20.0
0.0
Abs olute Dis parity
over the 20th Century, USA
Age-specific Mortality Differences between the
Richest and Poorest 20% of the World’s Population
100
Poorest 20%
Mortality Rate per 1000
RR
9
80
7
60
5
40
Richest 20%
20
0
3
1
4
0-
Gwatkin (2000)
14
5-
9
-2
5
1
4
-4
0
3
9
-5
5
4
9
-6
0
6
70
+
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
Control
Depression
Stress
behaviours
P-N-E
Immune Function
?
Traditional Risk
Factors
INTERHEART: PAR ~ 80%
CHD
Income Inequality, Poverty and Heart Disease: 1900-2000, USA
700
80
poverty
income
inequality
heart
disease
60
500
50
40
400
30
300
20
200
1900
1910
1920
1930
1940
1950
1960
1970
1980
1990
10
2000
gini coefficient/poverty
rate per 100,000
600
70
Race-specific Voting Participation in Presidential Elections
and age-adjusted, all-cause mortality, USA, 1968 - 1998
1,700.00
70.0
1,600.00
65.0
White Voting
1,400.00
60.0
1,300.00
Black Mortality
1,200.00
55.0
1,100.00
50.0
1,000.00
White Mortality
Black Voting
900.00
% Voting in Presidential elections
All-cause mortality per 100,000
1,500.00
45.0
800.00
700.00
40.0
1968
1970
1972
1974
1976
1978
1980
1982
1984
Year
1986
1988
1990
1992
1994
1996
1998
Lynch and Davey Smith (2003)
Sex-Specific Smoking Trends and Heart Disease, 1900-1998, USA
800
3000
700
2500
2000
AADR
500
400
1500
300
1000
200
Male Smoking
Female Heart Disease
500
Female Smoking
100
0
1900
0
1910
1920
1930
1940
1950
1960
1970
1980
1990
2000
Per Capita Consumption
Male Heart Disease
600
Sex-Specific Smoking Trends and Income Inequality, 1900-1998, USA
100
3000
Male
Smoking
90
2500
80
Income Inequality
2000
Female
Smoking
60
Gini
Per Capita Consumption
70
50
1500
40
1000
30
20
500
10
0
1900
1910
1920
1930
1940
1950
1960
1970
1980
1990
0
2000
Sex-Specific Cholesterol Trends and Income Inequality, 1980-2002, USA
47
5.6
46
5.5
45
5.4
44
43
Male Cholesterol
5.3
42
Gini
5.2
41
40
5.1
Female Cholesterol
39
5
38
37
4.9
1980
1985
1990
1995
2000
Total Cholesterol Trends from Minnesota Heart Survey: Arnett et al. Circulation (2005)
Conclusion
• 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.
Individual and Population Level Causation
Issues for PURE
Black Africans
700
600
500
Coloured
White
CHD
“Heart
Disease”
SEP
400
300
Risk
Factors
200
All Stroke
100
SEP
0
?
Stress
SEP
INTERHEART
Psychosocial – CHD
CHD
PAR ~ 30%
Psychosocial
Steyn, et al Circulation (2005)
PURE
Social, economic, demographic, behavioural transition

Major Risk
Factors
Social
Inequality
CHD
Psychosocial
Factors
Reporting
Tendency
Thank you
Triangulating Epidemiology
Populations
Disease Trends
Sub-groups
Populations
Individuals
Sub-groups
Biology
Individuals
Genetics
Biology
Disease
Genetics
Which social inequality is “better”?
CHD Rate / 100K
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?
Social
Disadvantage
Social
Advantage
Implications for Research on Human Growth and Development
• 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
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
Risk of CHD and Lung Cancer by Smoking Status
CHD (fatal or non-fatal)
Lung Cancer Death
Current or Former
Smoker
172 / 1000
15 / 1000
Never Smoker
12 / 1000
0
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+
High ed.
77
Mid ed.
84
Low ed.
89
CHD Risk per 1,000
65
15% 
83
128
97% 
(1997)