Department of Mental Health Sciences, Royal Free and University College Medical School, London
Department of Primary Care and Population Sciences, Royal Free and University College Medical School, London
Department of Mental Health Sciences, Royal Free and University College Medical School, London, UK
Correspondence: Dr D. P. J.Osborn, Department of Mental Health Sciences, Hampstead Campus, Royal Free and University College Medical School, Rowland Hill Street, London NW3 2PF, UK.Tel: +44 (0) 207 794 0500 x 3950; fax: +44 (0) 207 830 2808; e-mail: d.osborn{at}medsch.ucl.ac.uk
Declaration of interest None. Funding detailed in Acknowledgements.
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Aims To compare the main risk factors for CHD in people with and without SMI in primary care, to investigate the role of socio-economic variables, and to examine any association between antipsychotic medication and CHD risk.
Method Cross-sectional screening.
Results In total, 75 of 182 general practice patients with SMI and 150 of 313 such patients without SMI attended the interview. SMI was associated with: raised 10-year CHD risk scores (OR=1.8,95% CI 1.03.1); high-density-lipoprotein (HDL)-cholesterol levels <1.0 mmol/l (OR=4.0, 95% CI 1.510.7); raised cholesterol/HDL-cholesterol ratios (OR=1.8,95% CI 1.03.2); diabetes mellitus (OR=3.8,95% CI 1.113.3) and smoking (OR=3.0,95% CI 1.73.4). These associations varied significantly with age. Adjustment for unemployment did not fully explain the associations.
Conclusions Excess risk factors for CHD are not wholly accounted for by medication or socio-economic deprivation. There is an urgent need for CHD screening and for relevant interventions for smoking cessation and diabetes, as well as advice on diet and exercise, in patients with SMI.
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We aimed to compare the prevalence of the four most important risk factors for CHD (Khot et al, 2003) in people with and without SMI in primary care, and to compare the overall Framingham CHD risk scores (Hingorani & Vallance, 1999). One of our secondary aims was to investigate the role of socio-economic variables in any relationship between CHD risk and schizophrenia. Such factors have often been ignored, despite the fact that schizophrenia is strongly associated with adverse socioeconomic circumstances (Agerbo et al, 2004), as are CHD mortality and CHD risk factors (Brunner et al, 1999). Our other secondary aim was to investigate any association between antipsychotic medication and CHD risk.
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We collected data on age, gender, self-reported smoking status, prescribed medication and a number of socio-economic and demographic variables at interview. Recall of general practice diagnosis of ischaemic heart disease or diabetes mellitus was noted, as was the most recent body mass index measurement. The first two questions of the Rose Angina Questionnaire were used to screen further for undiagnosed ischaemic heart disease (Cook et al, 1989). Blood pressure was measured at the beginning and end of the interview using an automated sphygmomanometer (Whincup et al, 1992), and the mean value was determined. A non-fasting blood sample was taken for measurement of total cholesterol, high-density-lipoprotein (HDL)-cholesterol and random glucose levels. The Framingham risk score was calculated using commercial software (Hingorani & Vallance, 1999). This risk score is an algorithm of age, gender, HDL-cholesterol level, total cholesterol level, blood pressure, smoking and diabetic status. The scores are well established and are more powerful predictors of future CHD than individual risk factors. The absolute CHD risk score may underestimate excess CHD risk at younger ages, but the CHD risk score software also calculates the expected risk score for a persons age and gender. The difference between these two results provides a measure of a persons excess CHD risk.
The most recent diagnosis for patients with SMI was always confirmed by a letter from a consultant psychiatrist that was held in the general practice notes. The dose of medication in chlorpromazine equivalents was calculated (Bazire, 2003). If a patient was taking more than one antipsychotic, the chlorpromazine equivalents were summed. Dose as a percentage of the maximum British National Formulary dose was also calculated. As there is considerable interest in associations between CHD and olanzapine (Koro et al, 2002) and clozapine (Lund et al, 2001), we compared the CHD risk in patients who were taking either of these medications with the risk in those who were not. All of the participants gave their written informed consent, and ethical approval was obtained from the Royal Free Hospital and the Camden and Islington Community NHS Trust local research ethics committees.
Statistical analysis
Initial univariate associations between SMI and a variety of outcomes
guided which co-variates should be included in subsequent multivariate
analysis. If continuous variables were normally distributed, any association
with SMI was explored by linear multiple regression. Outcome variables, such
as CHD risk score and cholesterol level, were also dichotomised around
clinically or statistically significant values, allowing analysis of
associations by multiple logistic regression. Age and gender were included
a priori. Unemployment was included because on univariate analyses it
was the variable most consistently and robustly associated with both CHD risk
scores and individual risk factors for CHD. We tested the contribution of
variables and interaction terms by comparing models that included and excluded
the component of interest, using likelihood ratio tests. Any influence of the
sampling strategy by practice was first assessed by adding practice as a
covariate to final models. We then reassessed the statistical models using
survey techniques in Stata version 6 for Windows and examining for any design
effect using the design effect (DEFT) scores for each model. The
DEFT score quantifies the influence of the cluster design, as a ratio of the
cluster result to a simple random-sampling-design result.
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Characteristics of participants
The demographic and socio-economic profiles of the two groups are shown in
Table 1. The SMI group was
characterised by low levels of income, home ownership, car ownership and
employment. In total, 66 out of 74 participants (89%) in the SMI group had a
diagnosis of schizophrenia, 6 had a diagnosis of schizoaffective disorder, and
the remaining 2 had a diagnosis of a chronic or persistent delusional
disorder. Diagnoses had been made between 2 and 43 years previously (mean 14.6
years, s.d.=10.5). The number of inpatient psychiatric admissions in the past
5 years ranged from 0 to 8 (mean 0.93, s.d.=1.34). Only 9 patients (12%) lived
in sheltered or hostel-type accommodation. In total, 67 out of 74 patients
(91%) had been seen in psychiatric secondary care within the past 2 years, 56
(76%) within the past 9 months, but only 37 (50%) within the past 3 months.
Therefore many of these patients did not require the most intensive community
care.
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View this table: [in a new window] | Table 1 Demographic and socio-economic variables associated with severe mental illness (SMI) |
Psychiatric medication
In total, 20 out of 74 patients (27%) in the SMI sample were taking
long-acting intramuscular depot antipsychotics, and 35 patients (47%) were
taking atypical antipsychotics. Risperidone was not available as a depot
preparation as data collection took place between 1999 and 2002. The dose of
medication in chlorpromazine equivalents could be calculated for 49 patients.
The missing data are explained by the fact that some patients were prescribed
atypical antipsychotics such as olanzapine, without chlorpromazine equivalents
(Bazire, 2003). The median
chlorpromazine dose was 217 mg (interquartile range (IQR) 75433). The
dose as a percentage of the maximum British National Formulary dose
of antipsychotics could be calculated for 67 patients. The median was 25% (IQR
8.350). Significantly more people with SMI were currently prescribed
antidepressants, compared with the comparison group (18/74 (24%) v.
15/148 (10%);
2=7.8; P=0.005).
CHD risk score results
Univariate results
Patients with SMI had significantly lower HDL-cholesterol levels, and a
higher total cholesterol/HDL-cholesterol ratio, but showed little overall
difference in blood pressure (Table
2). They were also significantly more likely to smoke, to have a
diagnosis of diabetes and to have a raised overall CHD risk score for their
age and gender (Table 3).
Patients with SMI were twice as likely to have a raised Framingham risk score
for their age and gender compared with patients without SMI
(Table 3). Participants with
SMI had higher absolute 10-year CHD risk scores (median 10-year risk=5%; IQR
212) than participants without SMI (median 10-year risk=4%; IQR
29%) (MannWhitney U-test, z=2.0;
P=0.049).
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View this table: [in a new window] | Table 2 Cardiovascular risk factors and severe mental illness (SMI): continuous variables1 |
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View this table: [in a new window] | Table 3 Associations between categorical coronary heart disease (CHD) risk score variables and severe mental illness (SMI); results of logistic regression |
Multivariate analysis
Effect of increasing age. The magnitude of the difference in the
results between participants with and without SMI varied significantly with
age. More patients with SMI than controls exhibited raised 10-year CHD risk
scores, except above the age of 60 years
(Fig. 1). A logistic regression
model including an ageSMI interaction term, adjusted for age,
unemployment and gender, predicted having a raised CHD risk score better than
a model that did not include the interaction term
(Table 3). This is because the
odds ratios between SMI and excess CHD risk differ significantly according to
age group. The source of this interaction with age was explored further by
examining logistic models between SMI and each individual component of the CHD
risk score. The most likely sources of the interaction were smoking, total
cholesterol concentration and hypertension
(Table 3, column 7). These
individual factors are also shown according to age group in
Fig. 2. Both
Fig. 1 and
Fig. 2 suggest that the results
for patients over 60 years of age contradict the results for the younger
participants. For this reason, the main results were also explored in a
restricted sample from which the oldest age group (over 60 years) had been
excluded. Multiple regression analysis confirmed that patients with SMI in
this age group showed greater differences in CHD risk score (the difference
between personal CHD risk and expected CHD risk for the patients age
and gender) after adjustment for age, gender and unemployment
(Table 2, column 6).
![]() View larger version (14K): [in a new window] [as a PowerPoint slide] |
Fig. 1 Scatter plot of differences in 10-year coronary heart disease (CHD) risk
score according to age. SMI, severe mental illness. Example of excess CHD risk
calculation: if an individuals 10-year CHD risk score is 5%, and the
expected value for someone of the same age and gender is 2%, their excess risk
is calculated as (5%2%)=3%.
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![]() View larger version (25K): [in a new window] [as a PowerPoint slide] |
Fig. 2 Associations between severe mental illness (SMI) and excess coronary heart
disease (CHD) risk, smoking, high cholesterol level and high blood pressure in
different age groups. SBP, systolic blood pressure, DBP, diastolic blood
pressure.
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Effect of unemployment. With regard to continuous outcomes, the results were most pronounced in the under-60s (Table 2, compare columns 5 and 6). Presence of SMI still predicted a greater magnitude of excess CHD risk after adjustment for age, gender and unemployment. It also predicted higher total cholesterol/HDL-cholesterol ratios and lower HDL-cholesterol levels in this age group. For binary outcomes, unemployment partially explained the associations of SMI with a raised CHD risk score, smoking status and low HDL-cholesterol levels (Table 3). The inclusion of other socio-economic variables (listed in Table 1) in the multivariate models had little further effect on the main associations, and those data are not presented here.
Effect of medication. Among patients with SMI, few medication
variables were associated with excess CHD risk or with individual CHD risk
factors (Table 4). The
exception was higher doses of medication, which were associated with increased
CHD risk scores (most likely to be caused by increased smoking). In total, 10
out of 17 patients (59%) on olanzapine or clozapine showed a raised CHD risk
score, compared with 27 out of 55 patients who were not on such medications
(49%;
2=0.5, P=0.48). The proportion of individuals
who were diagnosed with diabetes was also higher among patients on these
medications, but again the trend was non-significant (3/18 (17%) v.
4/56 (7%);
2=1.4, P=0.23).
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View this table: [in a new window] | Table 4 Antipsychotic medication and coronary heart disease (CHD) risk in people with severe mental illness |
Design effect. Adding practice as a co-variate to the final models had little effect on any of the main results. The DEFT scores were close to 1 and were all less than 2, which also suggests that there was very little variation in effect between practices.
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The CHD risk of the oldest participants with SMI (>60 years) was less marked, with less smoking, dyslipidaemia and hypertension, possibly reflecting a healthy-survivor effect whereby the people with SMI who had the highest CHD risk factors had already died. It is not surprising that excess CHD risk factors are increasingly detected with advancing age, as they become more prevalent with age. Although people with SMI remain at increased risk of developing CHD even after their socio-economic circumstances have been taken into account, such adversity does explain some of the association.
Strengths and weaknesses of the study
The strengths of this study include the source of the participants and the
recruitment of a relevant comparison group from the same source as the
patients with SMI. The primary-care setting allowed recruitment of all
patients with SMI, not just those in secondary care. Previous cardiovascular
outcome research has often focused on institutionalised samples, or at least
on patients with the most chronic and disabling forms of the illness (e.g.
McCreadie, 2003). Our study
shows that excess CHD risk is not restricted to the sub-groups with SMI. The
reporting of the big four CHD risk factors
(Khot et al, 2003) of
the Framingham risk score, rather than one or two risk factors, is novel. The
contribution of socio-economic circumstances to inequalities in cardiovascular
health for people with SMI has previously been neglected.
The limitations of our study include its cross-sectional nature and the omission of any electrocardiogram measure for possible left ventricular hypertrophy. The latter was not included because of the weaker contribution of left ventricular hypertrophy to population CHD risk (Shaper et al, 1987; Khot et al, 2003), and because extensive electrocardiological studies in patients with SMI have not revealed an excess of left ventricular hypertrophy. Although diabetes was coded on the basis of general practitioner diagnosis, random blood glucose screening contributed to our main outcome. The increasing risk of diabetes in people with SMI justifies more intensive screening for the condition.
The response rate of approximately 45% might initially seem modest, but this is similar to rates for other community research involving blood tests, such as the Health Survey for England (47%; Erens & Primatesta, 1999). The possibility of bias was minimised but not eliminated by the incorporation of a comparison group. Criticisms of the Framingham scores or of dichotomising factors such as excess CHD risk, hypertension and hypercholesterolaemia apply to both groups, and measurement error could explain the results only if inaccuracy preferentially favoured the group with or the group without SMI. Selection bias has been carefully considered previously (Osborn et al, 2003). Although patients who frequently consulted their general practitioner were more likely to participate, again this was true for both groups. No psychiatric, medication or socio-demographic variables predicted participation in the study.
There was a non-significant difference in gender distribution, with more women in the non-SMI group (Table 1). Although this could potentially exaggerate the excess CHD risk factors in patients with SMI, continuous variables (Table 2) and odds ratios (Table 3) changed little after adjusting for age and gender, especially in patients under 60 years of age.
The study was neither powered nor designed to examine sub-groups or effects of atypical antipsychotics, so those results should be interpreted with caution.
Importance
Socio-economic determinants of health are now one of the main priority of
the World Health Organization
(2004), and there is no better
example of how such determinants affect health than patients with SMI.
However, we have demonstrated that SMI itself can incur CHD risk, over and
above that associated with the socio-economic deprivation experienced by these
patients. Our results emphasise the clinical necessity for CHD risk factor
screening for people with SMI. The burden of individual CHD risk factors may
be further compounded by the problems of weight gain
(Blackburn, 2000) and impaired
glucose control linked to the use of antipsychotics
(Haddad, 2004), and the
arrhythmogenic properties of conventional and newer antipsychotic drugs
(Glassman & Bigger, 2001).
This highlights people with SMI as candidates for more intensive CHD-focused
interventions. This study has identified the need to develop focused
interventions for smoking cessation, screening for diabetes and advice on
diet, exercise and other methods of enhancing HDL-cholesterol levels and
reducing the risk of CHD in people with SMI. Questions about the best form,
clinical setting and intensity of such interventions therefore require urgent
attention. Since around half of the patients who were invited to participate
took up our CHD screening offer, more opportunistic screening may be indicated
when patients are seen for other clinical reasons.
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LIMITATIONS
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D.O. was funded by a UK Medical Research Council Research Fellowship in health services research. The study received additional funding from the North Central Thames Primary Care Research Network.
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