Medical Research Council, Social Genetic and Developmental Psychiatry Centre, Institute of Psychiatry, London
Department of Psychiatry, St Bartholomews and Royal London Medical School, London
Department of Psychological Medicine, Wales School of Medicine, Cardiff University, Cardiff
Department of Psychiatry, University of Birmingham, Queen Elizabeth Psychiatric Hospital, Birmingham
Department of Psychological Medicine, Wales School of Medicine, Cardiff University, Cardiff
Medical Research Council, Social Genetic and Developmental Psychiatry Centre, Institute of Psychiatry, London, UK
Correspondence: Dr Anne Farmer, Medical Research Council, Social Genetic and Developmental Psychiatry Centre, Institute of Psychiatry, De Crespigny Park, London SE5 8AF, UK. Email: a.farmer{at}iop.kcl.ac.uk
None. Funding detailed in Acknowledgements.
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Few studies have examined the rates of physical disorders in those with recurrent depression.
Aims
To examine self-reported physical disorders in people with recurrent depression compared with a psychiatrically healthy control group.
Method
As part of a genetic case–control association study, 1546 participants with recurrent depression and 884 controls were interviewed about lifetime ever treatment for 16 different physical health disorders.
Results
The cases group had a significantly higher frequency of 14 physical disorders and more obesity than the control group. After controlling for age, gender, body mass index (BMI) and multiple testing, those in the cases group had significantly higher rates of gastric ulcer, rhinitis/hay fever, osteoarthritis, thyroid disease, hypertension and asthma.
Conclusions
People with recurrent depression show high rates of many common physical disorders. Although this can be partly explained by BMI, shared aetiological pathways such as dysfunction of the hypothalamic–pituitary axis may have a role.
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Control participants were recruited through the UK general practice-based Genetic–Environmental Nature of Emotional States in Siblings (GENESiS) study,4 and all were screened by telephone interview. Individuals were included in the control group if they had no past or present psychiatric disorder, were aged 18 years or over and were of White European origin. All participants gave written informed consent and the protocol was approved by the local ethics committees of the three participating institutions.
Diagnostic instruments
All participants with depression were given a face-to-face semi-structured
diagnostic interview, the Schedules for the Clinical Assessment of
Neuropsychiatry (SCAN) version
2.1,5 by trained
interviewers to establish the diagnosis of recurrent depression according to
either DSM–IV–TR or
ICD–10.6,7
Items of psychopathology were rated for severity and duration for the
peak-intensity 4–6 weeks of symptoms (i.e. symptoms were at their worst)
occurring during their worst and second-worst episodes of depression. The
computerised version of the SCAN 2.1 is built on the iSHELL system, which is a
computer-aided personal interviewing tool produced by the World Health
Organization,8 and
which provides DSM–IV and ICD–10 operationally defined diagnoses.
Potential control group participants were interviewed by telephone using a
modified version of the Past History
Schedule,9 and were
included if there was no evidence of past or present clinically significant
psychiatric disorder. All participants also completed the Beck Depression
Inventory10 to
measure their mood at the time of interview.
For the lifetime diagnosis of physical health disorders, a short structured interview was given in which all participants in the cases and control groups were asked whether they had ever been treated by their general practitioner for the following health problems: asthma, diabetes (insulin-dependent and non-insulin-dependent), epilepsy, gastric ulcer, hypercholesterolaemia (elevated blood lipids), hypertension, kidney disease, liver disease, myocardial infarction, osteoarthritis, osteoporosis, rheumatoid arthritis, rhinitis or hay fever, stroke or thyroid disease. Their replies were scored as yes, no or uncertain. For the purpose of the analyses reported here, ratings scored as uncertain were recoded conservatively as no. The interview was given face to face for the cases group and by telephone interview for the control group.
In order to check the accuracy of self-report, the general practitioners of 30 representative participants (cases and controls) from this study, combined with 47 euthymic participants from a genetic case–control study of bipolar affective disorder who had also been interviewed about their physical health, were asked to complete a checklist regarding the medical disorders listed above and asked to indicate whether their patient had ever been treated for any of these disorders. Kappa statistics for self-report compared with general practitioner report for six of the more common disorders were calculated.
Body mass index
For the cases group, self-reported height and weight were recorded in the
SCAN interview. Control participants were asked their current height and
weight in the telephone interview. These data were used to calculate the BMI
for each participant.
Data analysis
All phenotypic information from interviews and questionnaires was coded by
assigning a number to each participant and removing any personal identifying
information. This was first entered on an Excel spreadsheet, after which a
data file was created using the Statistical Procedures for the Social Sciences
(SPSS) version 11 for Windows for the statistical analyses. Group comparisons
of the lifetime prevalence of the different physical health disorders were
performed using simple contingency table analyses and binary logistic
regression. In the logistic regression analyses, significance was assessed
using the Wald statistic which is asymptotically distributed as a chi-square.
Since several medical disorders are related to obesity, the participants were
assigned to three BMI categories: normal (BMI under 25 kg/m2),
overweight (BMI 25 kg/m2 or over but less than 30 kg/m2)
and obese (BMI 30 kg/m2 or more). These categories were entered
into the logistic analyses as a co-factor. As there was a significantly
greater proportion of women in the cases group than in the control group,
gender was also entered in the logistic analyses as a co-factor. Similarly,
since physical disorders occur more frequently with increasing age, all
participants were scored according to whether they were at or above (scored as
1) or below (scored as 0) the median age.
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Sixty-nine per cent of the cases group were women compared with 56% of the
control group (
2=38.72, d.f.=1, P<0.001). In view
of this significant difference, gender was controlled for in all comparisons
of medical disorders. The mean age at interview of the cases group was 47.37
years (s.e.m.=0.31) and for the control group it was 47.71 (s.e.m.=0.32;
Students t=0.77, d.f.=2142.51). The median age of the sample
was 49.00 years.
Participant differences between sites
Participants from Birmingham were slightly older at interview (mean 49.33
years, s.d.=12.21) than those from Cardiff (mean 47.10 years, s.d.=13.64) and
London (mean 45.82 years, s.d.=10.60). In the cases group, those from London
were younger (mean 21.27 years, s.d.=11.74) than those from Birmingham (mean
25.08 years, s.d.=11.99) and Cardiff (mean 23.82 years, s.d.=10.91) at the
start of their depressive illness, and Cardiff recruited a higher percentage
of female participants (74%) compared with London (67%) and Birmingham
(65%).
Body mass index
Forty-two per cent of the cases group and 58% of the control group were of
normal weight, whereas 34% of the cases and 32% controls were overweight, and
24% cases and 10% controls had a body weight within the obese range. Men in
the cases group had significantly higher BMI values compared with men in the
control group: cases group mean=27.07 kg/m2, s.d.=4.78, range
14.36–50.18; control group mean=26.02 kg/m2, s.d.=4.55, range
14.94–62.70 (t=–2.76, d.f.=512.47, P=0.006).
Similarly, women in the cases group had significantly higher BMI values than
women in the control group: cases group mean=26.85 kg/m2,
s.d.=6.04, range 16.02–53.15; control group mean=24.51 kg/m2,
s.d.=4.66, range 16.56–51.79 (t=–7.01, d.f.=746.85,
P<0.001).
Self-reported medical disorders
Comparison with general practitioner report
Sixty-one of the 77 general practitioners (79%) completed questionnaires
regarding the medical histories of their patients. A further 5 general
practitioners returned the forms uncompleted, commenting that the participant
was no longer registered with the practice. Eleven general practitioners
failed to respond.
The majority of disorders were reported infrequently by both participants
and general practitioners. In addition, patients with bipolar disorder from
the genetic study sample were not asked about gastric ulcer or thyroid
disease, and none of the general practitioners reported hay fever among these
participants; hence these disorders were not included in the reliability
analyses. The kappa coefficients for the following medical disorders in
participants were as follows: asthma
=0.73 (s.e.m.=0.11), diabetes
=0.91 (s.e.m.=0.06), hypertension
=0.87 (s.e.m.=0.06),
hypercholesterolaemia
=0.65 (s.e.m.=0.10), myocardial infarction/angina
=0.82 (s.e.m.=0.13) and arthritis
=0.74 (s.e.m.=0.14).
Percentage agreement between general practitioners and participants for the
presence or absence of a medical disorder was 93%. The mean kappa coefficient
for the six disorders in the participants participating in the two studies was
0.79 and the mean s.e.m. was 0.10 (P<0.001).
Cases v. controls
Lifetime prevalence rates for common medical disorders in the cases and
control groups are shown in Table
1. Hypertension, asthma and osteoarthritis had the highest
lifetime prevalences in the cases group (16.49%, 16.48% and 10.67%
respectively) and asthma, hypertension and hypercholesterolaemia the highest
lifetime prevalences in the control group (9.39%, 7.13% and 6.10%
respectively). Five disorders had low prevalence in both cases and controls,
namely insulin-dependent diabetes, epilepsy, kidney disease, liver disease and
stroke. With the exception of insulin-dependent diabetes and kidney disease,
all other disorders were reported significantly more frequently in cases than
controls.
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View this table: [in a new window] | Table 1 Lifetime prevalence rates of self-reported medical disorders in the sample |
Table 2 shows the odds ratios, 95% confidence intervals, Wald statistic and significance for the binary logistic regression for cases compared with controls for each medical disorder from Table 1, for which there was a significant difference on the simple contingency tests (14 disorders). Presence or absence of the disorder was the outcome variable, and affected status (case or control), BMI (normal, overweight or obese), gender and age (at/above or below the median) were co-factors. A Bonferroni correction for multiple testing was applied. The table shows that the odds ratios for comorbid medical disorders and depression that remained significant following the Bonferroni correction after controlling for BMI, gender and age, were for gastric ulcer, rhinitis/hay fever, osteoarthritis, thyroid disease, hypertension and asthma (odds ratios 4.31, 3.29, 3.05, 2.78, 2.20 and 2.19 respectively).
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View this table: [in a new window] | Table 2 Binary logistic regression with presence or absence of each medical disorder as the outcome variable, and affective status (case or control), body mass index (<25, 25-29 or 30+ kg/m2), gender and age (above or below the median age) as co-factors |
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Body mass index
Both men and women in the cases group had significantly higher BMIs
compared with men and women in the control group. Although the percentages of
the two groups were similar in the overweight range (BMI 25–29
kg/m2), a greater proportion of the cases group were in the obese
range (BMI 30 kg/m2 and over) and substantially fewer were in the
normal range (BMI <25 kg/m2) compared with controls. Thus,
around a quarter of the men and women with depression were categorised as
obese, which increases their susceptibility to the attendant physical health
problems. In this study obesity was associated with an increase in
self-reported rates of hypercholesterolaemia, type II diabetes and myocardial
infarction. High rates of obesity may be caused by the weight-gaining
properties of some antidepressant medication, or because people who are
depressed take less exercise and/or comfort eat. However, it is
also possible that factors such as a shared common heritable pathogenesis may
be operating.11
Whatever the mechanism, this and other
studies11,12
suggest that clinicians need to pay more attention to the weight of their
patients with recurrent depression.
Comparison with other studies of physical disorders and depression
There have been many more studies examining rates of depression in those
with specific physical disorders than those investigating the physical health
of those with major depression. Noteworthy in relation to our findings is the
study by Taylor et al, who observed that ulcers occurred ten times
more frequently in elderly participants with depression compared with controls
without
depression,13 and a
recent literature review suggested that depressive symptoms are more common in
people with asthma than in members of the general
population.14 It
has also been shown that individuals with any history of allergy (including
rhinitis/hay fever) are significantly more likely to be diagnosed with major
depression.15 The
link between thyroid dysfunction and depression has been well-established, and
a recent large, register-based study in Denmark showed that patients
hospitalised with hypothyroidism had a greater risk of a subsequent admission
with depression or bipolar disorder than
controls.16
Previous studies have shown elevated blood pressure associated with
depression,17 as we
have found in our study, and prospective studies have also suggested that
depression may be a risk factor for the development of
hypertension.18 The
association between depression and chronic painful conditions such as
osteoarthritis is also
well-recognised,19
with studies showing that treatment of depression also reduces somatic
symptoms.
One large epidemiological study undertaken by the New Mexico Department of Health and Centers for Disease Control and Prevention in the USA examined the association between physical disorder and the 1-month prevalence of depression in over 5000 participants from the general population.20 In this study, 30% of participants with depression were obese (BMI 30 kg/m2 and above), i.e. 5–6% more than were found in the study reported here. Compared with individuals without depression, participants with depression were significantly more likely to report treatment for hypertension, asthma and arthritis. However, the New Mexico study did not control for possible confounding factors.
In another large epidemiological study of physical illness and depression, the Canadian Community Health Survey,1 115 071 participants were screened by self-report questionnaire for physical diagnoses and a brief medical interview was used to diagnose depression in the previous year. As this Canadian survey was one of the largest studies reporting depression in range of physical disorders, it is reasonable to compare their results with ours despite methodological differences. Although they controlled only for age and gender and not for BMI in their logistic regression analyses, none the less these authors found significant odds ratios for co-occurring depression of 2.8 for ulcers, 1.9 for both asthma and arthritis, 1.4 for thyroid disease and 1.2 for hypertension, which are comparable to our findings for these disorders.
Evidence from our own and the above-mentioned studies lends some support for the hypothesis that there are shared aetiological factors between recurrent depression, obesity and the six physical disorders. One possible mechanism includes a role for stress and activation of the hypothalamic–pituitary–adrenal (HPA) axis.21 Elevated cortisol level is a frequent finding in depression, and it has been proposed that this may be caused by both acute and/or protracted exposure to stress.22 Hypercortisolaemia in Cushings syndrome is associated with gastric ulcers and obesity. Activation of the HPA axis has been shown to exert hyperphagic and antithermogenic effects,23 and visceral obesity may be associated with increased cortisol clearance. Hence, abnormal cortisol regulation may link both obesity and gastric ulcers with depression. Proinflammatory cytokines are produced in excess in people with asthma, rhinitis and possibly also osteoarthritis,24 and these cytokines are also associated with inflammatory activation of the HPA axis.15 Similarly, Nyklicek et al have shown that people with hypertension had an enhanced HPA axis and immune system reactivity to stress.25 Hence HPA axis activation from inflammatory processes could link depression with asthma, hay fever, osteoarthritis and hypertension. Various studies have shown abnormalities of the hypothalamic–pituitary–thyroid axis in depression,26 which suggests that central hypothalamic–pituitary dysfunction may be associated with thyroid abnormalities in addition to dysfunction in the glucocorticoid system.
Clearly, all of the above is speculative and requires confirmation from further studies. The limitations of our study also need to be considered; for example, the large sample size imposed some methodological constraints. Although we carefully defined participants and controls in terms of the presence or absence of recurrent depression by undertaking a detailed semi-structured interview, we relied on self-report with regard to physical health problems as well as height and weight to calculate BMI. We hoped that asking directly about treatment received for the physical disorders would have ensured that some form of medical intervention had occurred and that the diagnosis would have been made by a doctor. This would seem to be the case, since in a sample of 61 people with affective disorders and controls, the presence or absence of physical disorder was confirmed by their general practitioner 93% of the time. In addition, the kappa coefficients for individual disorders ranged from 0.65 to 0.91, indicating substantial to almost perfect agreement.27 Thus, we are confident that self-report gives a reasonably accurate account of comorbid medical disorders in these participants. Second, despite our having recruited over 2000 individuals and having found significant differences between cases and controls for a number of physical health disorders, the frequencies of several disorders were low, limiting the power to detect significant odds ratios in the less common disorders. Also, the average age of participants was the mid-forties, so the majority of them had not reached the period of risk for many of the physical illnesses. Third, it is also possible that retrospective rating by participants with recurrent depression of their physical health could have been influenced by their present mood. Indeed, we did find a small but significant correlation between scores on a self-report measure of present mood, the Beck Depression Inventory,10 and number of medical disorders reported in both cases and controls. However, Beck Depression Inventory score contributed only 1.5% of the variance in number of physical disorders reported in cases and 1% in controls. Last, we used BMI as a measure of obesity, and there is now evidence that it is abdominal or visceral fat deposition that is most harmful to health.11 Consequently, waist measurement or waist/hip ratio would have been a more accurate measure of the risk of obesity to physical health.
Although long neglected, the physical health of those with schizophrenia is beginning to be addressed, particularly in relation to the weight gain associated with antipsychotic drugs. Our study suggests that attention also needs to be paid to the physical health needs of people with depression.
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