Institut National de la Santé et de la Recherche Médicale (INSERM) U888, University of Montpellier, France
INSERM U888, Montpellier, France and Kings College London, Institute of Psychiatry, London, UK
INSERM U888, University of Montpellier
INSERM U593, University of Bordeaux
INSERM U708, University of Paris
INSERM U888, University of Montpellier, France
Correspondence: Dr Marie-Laure Ancelin, INSERM U888, Nervous System Pathologies, Hôpital La Colombière, P42, 34093 Montpellier Cedex 5, France. Email: ancelin{at}montp.inserm.fr
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Depression may increase the risk of mortality among certain subgroups of older people, but the part played by antidepressants in this association has not been thoroughly explored.
Aims
To identify the characteristics of older populations who are most at risk of dying, as a function of depressive symptoms, gender and antidepressant use.
Method
Adjusted Cox proportional hazards models were used to determine the association between depression and/or antidepressant use and 4-year survival of 7363 community-dwelling elderly people. Major depressive disorder was evaluated using a standardised psychiatric examination based on DSM–IV criteria and depressive symptoms were assessed using the Center for Epidemiological Studies–Depression scale.
Results
Depressed men using antidepressants had the greatest risk of dying, with increasing depression severity corresponding to a higher hazard risk. Among women, only severe depression in the absence of treatment was significantly associated with mortality.
Conclusions
The association between depression and mortality is gender-dependent and varies according to symptom load and antidepressant use.
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The objective of our study was to examine the association between depression and mortality in a large community-based elderly population, which permitted the examination of a wide range of clinical profiles and extensive adjustment for confounding factors. Analysis of gender differences and the impact of antidepressant use were also considered.
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Depression measures
The Mini International Neuropsychiatry Interview
(MINI),16 a
standardised psychiatric examination which has been validated in the general
population, was used for the diagnosis of current major depressive disorder,
according to DSM–IV
criteria.17
Severity of depressive symptoms was assessed using the 20-item Center for
Epidemiology Studies–Depression scale
(CES–D);18
information was also gathered on the participants history of major
depressive episodes throughout their lifetime, to identify those with incident
depression (one episode) v. recurrent depression (two or more
episodes).
For the analysis, participants were classified into one of three groups. Severe depression included participants with a current major depressive disorder or a CES–D score of 23 or over, allowing for the fact that some participants with severe symptoms did not reach DSM classification criteria, most commonly because of the duration of symptoms. Mild depression was defined as a CES–D score between 16 and 22 and no depression included participants with a CES–D score lower than 16.
Current use of antidepressants was validated by presentation of the prescription or the medication itself and the type of medication was noted according to the World Health Organizations Anatomical Therapeutic Chemical (ATC) classification.19
Mortality
The follow-up time for this analysis was 4 years, with a median of 3.7
years for both men and women. For the participants who died during this
period, information on the exact date and cause of death was determined
respectively from death registries and medical records (based on the
ICD–10).20
All-cause mortality was the principal outcome defined for this analysis;
however, cause-specific mortality was also examined.
Other measures
At inclusion, information was obtained on socio-demographic and lifestyle
characteristics, as well as overall health. Participants were classified as
disabled if they were unable to complete at least two tasks from either the
Instrumental Activities of Daily Living
(IADL)21 or the
Activities of Daily Living
(ADL)22 scales.
Cognitive function was assessed using the Mini-Mental State Examination
(MMSE).23 Within
each centre, participants scoring less than the 10th percentile for their age
(four groups) and education level (four groups) were classified as cognitively
impaired. This method of classifying cognitive impairment, compared with that
based on an unadjusted MMSE score below 26, did not change the results of the
study.
Detailed medical questionnaires were used to obtain information on history
of vascular diseases (including angina pectoris, myocardial infarction,
stroke, cardiovascular surgery, bradycardia or palpitations), other chronic
illnesses (asthma, diabetes; fasting glucose
7.2 mmol/l or reported
treatment), hypercholesterolaemia (total cholesterol
6.2 mmol/l),
hypertension (resting blood pressure
160/95 mmHg or treated) and thyroid
problems) and diagnoses of cancer within the past 2 years. Participants were
classified as having comorbidity if they had one or more of these illnesses.
Hospitalisation for a non-traumatic illness within the past 2 years was also
used as a measure of health status.
The multivariate analysis controlled for all covariates that have been
reported to be confounding factors in relation to depression and
mortality;4,6,12,14
age (continuous), education level (<12 v.
12 years of
schooling), living situation (alone v. with others), current alcohol
consumption (binary: <24 v.
24 g per day), current smoking
status (binary: <200 v.
200 cigarettes per year), body mass
index (BMI;
18, 18–30 or
30 kg/m), disability (yes/no),
cognitive impairment (yes/no), comorbidity (yes/no) and recent hospitalisation
(yes/no).
Statistical analysis
Two-tailed chi-squared tests were used to compare the baseline
characteristics between men and women and to determine differences in
unadjusted characteristics between participants with and without depressive
symptoms, or between antidepressant users and non-users. Cox proportional
hazards analysis was used to model the risk of mortality during the follow-up
period. The age of participants at inclusion was taken as the basic
timescale24 to
account for the non-proportionality in risk of mortality with age among the
elderly,4,14
and Cox models with delayed entry were used. To estimate the risk associated
with current depression or antidepressant use, models were generated with
reference to non-depressed (no major depression and CES–D score <16)
or non-treated participants respectively. When the combined effects of
depression and antidepressant treatment were examined, participants who were
currently neither depressed nor using treatment were the reference group.
Unadjusted models were initially constructed for each of the factors of interest, controlling only for study centre. Owing to the statistically significant interactions between gender and both depression (mild: z=–0.76, d.f.=1, P=0.004; severe: z=–1.34, d.f.=1, P<0.001) and antidepressant use (z=–1.44, d.f.=1, P<0.001), all subsequent analysis was undertaken separately for men and women. Multivariate analysis was used to determine the hazard associated with current depression and/or antidepressant treatment, while adjusting for the potential confounding factors and stratifying by gender. There was no indication of collinearity between any of the covariates and no statistically significant interaction terms in the adjusted models. The software SAS version 9.1 for Windows was used for all of the statistical analysis and the significance level was P<0.05.
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2=162, d.f.=1, P<0.001), live alone
(
2=39.8, d.f.=1, P<0.001), have lower education
(
2=3.99, d.f.=1, P=0.05), be underweight
(
2=8.9, d.f.=1, P=0.003), have disabilities
(
2=398, d.f.=1, P<0.001) and cognitive impairment
(
2=63.9, d.f.=1, P<0.001) have comorbidity
(
2=12.9, d.f.=1, P<0.001) and to have been
hospitalised recently (
2=12.4, d.f.=1, P<0.001).
They were also more likely to be using antidepressants
(
2=25.8, d.f.=1, P<0.001), to be depressed
(
2=11.1, d.f.=2, P=0.004) and to have died during the
follow-up period (
2=156, d.f.=1, P<0.001). There
was, however, no difference in the gender ratios of participants included in
the analysis and those who were not. Baseline characteristics of the 7363 participants in the analysed sample are summarised in Table 1. The majority were female (60.8%) with a mean age of 74 years (range 65–93). With the exceptions of centre, obesity and adjusted MMSE score, men and women differed significantly in all of the covariates examined.
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View this table: [in a new window] | Table 1 Baseline characteristics of the sample: men v. women (n=7363) |
Prevalence and correlates of depression
The prevalence of severe depression (major depressive disorder or
CES–D
23) was 10.2%, including 1.8% diagnosed with major depressive
disorder, whereas that of mild depression (CES–D 16–22) was 12.1%
(Table 2). Women had a
significantly higher prevalence of depression than men and were more than
twice as likely to use antidepressants. Among those using antidepressants,
over half were taking selective serotonin reuptake inhibitors (SSRIs) and a
relatively high number used tricyclic antidepressants.
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View this table: [in a new window] | Table 2 Depression characteristics of the sample at baseline: men v. women |
Compared with the non-depressed group, those with either mild or severe
depression were more likely to live alone (
2=139, d.f.=2,
P<0.001), have disability (
2=46.5, d.f.=2,
P<0.001), cognitive impairment (
2=43.6, d.f.=2,
P<0.001) and comorbidity (
2=14.3, d.f.=2,
P<0.001). Women with depression were also of lower education
(
2=15.4, d.f.=2, P<0.001) and were more likely to
have been hospitalised recently (
2=9.24, d.f.=2,
P=0.01), whereas men with depression were older
(
2=10.5, d.f.=2, P=0.005).
Incidence and correlates of mortality
The total follow-up time for the study was 26 165 person-years and during
this period 380 participants (5.2%) died, with a higher proportion of the
deaths among men (7.5%) than women (3.7%). Recent hospitalisation
(
2=37.9, d.f.=1, P<0.001), comorbidity
(
2=24.6, d.f.=1, P<0.001) and disability
(
2=83.9, d.f.=1, P<0.001) were all significantly
associated with mortality in both men and women, as was increasing age
(
2=82.4, d.f.=1, P<0.001). Cognitive impairment
(
2=8.8, d.f.=1, P=0.003) and current smoking
(
2=8.05, d.f.=1, P=0.005) were associated with
mortality in men only. Alcohol consumption, educational level, living alone
and BMI were not significantly associated with mortality, but were retained in
the adjusted models because of their correlation with mortality at the 20%
significance level and because previous reports suggest that they confound the
depression–mortality association.
Associations between mortality and depression severity or antidepressant use
We first evaluated the separate effects of depression and antidepressant
use on 4-year survival. For men, there was an apparent severity-dependent
association between depression and mortality
(Table 3). Compared with
non-depressed men at inclusion, a higher percentage of men with mild
depressive symptoms died during follow-up and the percentage of those with
severe depression who died was even higher. In site-adjusted Cox models
depression severity was positively associated with mortality risk. In models
adjusted for a range of covariates a similar trend was seen, but only severe
depression remained significantly associated with mortality. For men taking
antidepressants, the percentage of deaths was almost three times that for men
not receiving such treatment. This corresponded with a significantly increased
mortality risk for antidepressant users in the univariate Cox analysis, which
remained significant after adjustment for covariates. There was no difference
in mortality risk according to type of antidepressant treatment.
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View this table: [in a new window] | Table 3 Cox proportional hazard models for the risk associated with depression or antidepressant use among elderly men (n=2886) |
In contrast, among women the overall risk associated with depression was less marked, and similar effects were seen regardless of depression severity (Table 4). Mild and severe depression were significantly associated with mortality in univariate analysis, with women having approximately one and a half times the risk of dying during follow-up compared with non-depressed women. After multivariate adjustment the risk associated with depression remained similar in strength, although reduced in significance for both mild and severe depression. Antidepressant use was not associated with 4-year survival in either univariate or multivariate analysis, with a similar percentage of women dying in the group taking antidepressants and in the group that did not.
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View this table: [in a new window] | Table 4 Cox proportional hazards models for the risk associated with depression or antidepressant use among elderly women (n=4477) |
Combined effects of depression and antidepressant use
To investigate further the association between depression and mortality,
participants were then grouped according to depression severity and use of
antidepressants (Table 5).
Overall there was little change in the significance of the associations found
between the univariate and multivariate analysis, with relatively minor
differences in the hazard ratios.
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View this table: [in a new window] | Table 5 Cox proportional hazards models for the combined effect of depression severity with or without antidepressant treatment, separately in elderly men (n=2886) and women (n=4477) |
Among men, the largest mortality risk was seen in the group with severe depression who were taking antidepressants, and there was also an increased mortality risk for those taking antidepressants who had mild depressive symptoms. In contrast, non-depressed men using antidepressants did not have an increased mortality risk. For the men who were not using antidepressants, minor depression was not associated with 4-year survival, but severe depression appeared to increase risk, just failing to reach significance.
When we considered separately the small number of men with current major
depression (diagnosed using the MINI), similar results were obtained to those
found in the severe depression group. Men taking antidepressants had a
significantly increased risk of dying (adjusted HR 6.2, 95% CI 2.2–17.3;
2=12.0, d.f.=1, P<0.001) and there was also a
trend for increased risk among men without treatment, but this did not reach
the threshold for significance (adjusted HR=2.3, 95% CI 0.5–9.9;
2=1.28, d.f.=1, P=0.2).
Although similar hazard ratios were seen for the different groups of women (Table 5), the associations appeared strongest in the group of women who were depressed but not using antidepressants. In fact, in the adjusted models it was only severe depression in the absence of antidepressant treatment that significantly increased mortality risk.
We examined separately the risk associated with incident and chronic major depressive episodes, which affected 5.4% (3.7% of men, 6.7% of women) and 4.5% (2.1% of men, 6.2% of women) of participants respectively (see online data supplement, Table DS1). For men with one depressive episode there was a trend for increased mortality risk; however, no such increase in risk was observed for those with recurrent depression. In women, neither incident nor recurrent episodes were significantly associated with mortality. In addition, the number of depressive episodes did not predict mortality risk in men and women when these factors where included in the multivariate models containing depression and antidepressant use (data not shown).
Cause of death
The majority of participants died from causes related to cancer (men 33%,
women 41%) or cardiovascular disease (men 24%, women 18%), with fewer dying
from respiratory problems (men 7%, women 6%). A substantial number died from
unknown causes (17%), which is probably the result of multiple disorders and
an overall decline in general health. There were very few suicides (four in
total) and only five deaths due to external causes such as accidents.
When examining a specific cause of death as the outcome variable in the multivariate adjusted Cox models (see online data supplement, Table DS2), mild depression in women significantly increased cardiac-related death. Severe depression in men resulted in an increased risk of death from all three causes that were examined (cardiac-related, tumour-related or unknown). Antidepressant treatment in men was associated with an increased risk of death from an unknown cause. The number of participants dying from other causes was too small to allow accurate analysis.
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Gender differences in depression-related mortality risk
Our study suggests that the relationship between depression and mortality
is not only gender-dependent but also depends on the severity of depression.
The findings of increased mortality risk among certain subgroups remained
significant even after controlling for a large number of variables, including
several measures of health status. Therefore our results do not support the
suggestion that declining health explains in large part the association
between depression and
mortality.14
It has been reported that increasing depressive symptoms8,25 are associated with incrementally higher mortality risk; however, from our gender-stratified analysis we found that this was only the case for men. In women the overall association between depression and mortality was less marked, with non-significant adjusted associations and no apparent increase according to depression severity. These gender variations could be the consequence of differences in the nature or intensity of exposure to risk factors, or in the susceptibility to the same risk factors. They could result from cultural, social, behavioural or adaptive differences. Women tend to report a greater number of symptoms and a higher degree of distress26 and may differ from men in their perceived need and willingness to seek treatment. Depression is less likely to be recognised in men27 and therefore the presence of detectable depressive symptoms in elderly men could also signify a more extreme condition,28 which might account for the stronger associations with mortality, even for mild depression. Another possibility is that in older people with depression, men are more likely to die and women to be first disabled. This hypothesis could be tested with a longer follow-up period.
Our finding that incident depression – but not chronic depression – increases mortality risk in men only, has been reported previously.6 However, our study suggests that this factor is secondary to the association between depression severity and/or antidepressant use, as it was not significantly associated with 4-year survival when included in the models presented. It should be noted, however, that there was a higher rate of missing data regarding previous episodes in currently depressed participants, and therefore this finding requires further validation.
Gender differences in antidepressant-related mortality risk
Despite our finding that antidepressant use in depressed men was associated
with increased mortality risk, no such association was found in non-depressed
men who used antidepressants, arguing against the pharmacological adverse
effects of the antidepressants as a potential cause. Assuming that these
treated participants were formerly depressed, this would indicate rather that
adequate treatment of depression results in a reduction in the increased
mortality rate. Likewise, the presence of depressive symptoms despite
treatment could be an indication of depression severity, rather than
non-efficacy of treatment, and therefore this increased depression severity
could account for the higher mortality risk among this group.
In quite a different manner, only women with untreated severe depression had an increased risk, suggesting a positive impact of treatment even in women with residual symptoms. These results could highlight gender differences in the prescription and use of antidepressants, or in treatment adherance. It might also be that women respond better to specific types of antidepressant treatment than men,29 although this has rarely been reported in the case of post-menopausal women, and therefore depressed women receiving treatment may be better off than their male counterparts. Even when individuals respond to antidepressant treatment, they can still maintain clinically diagnosable depression.28 The treatment may be effective but need to be given for a longer period, or the depression may be resistant to treatment. This raises the question of the dosage and/or reduction in depression symptoms required for both men and woman. Overall, these results emphasise the importance of stratifying the analysis by gender, with clear gender differences in mortality risks.
Interestingly, we found no significant difference in mortality risk when we compared the different types of antidepressants, despite suggestions that SSRIs and tricyclic antidepressants have differential effects on cardiovascular health.30 Benzodiazepine-related medications, which are used to treat anxiety and are often administered in combination with or in place of antidepressants,31 were not associated with mortality risk in either men or women. In addition, this factor did not confound the associations reported here (data not shown).
Why is depression associated with increased mortality?
The relationship between depression and mortality is thought to result from
a combination of factors. Depression appears to exacerbate the outcome of
medical illness,1
even in appropriately adjusted analysis, and it is possible that depression
acts as a proxy marker for the severity of physical ill health. Psychological
wellbeing also has a role, with loss of motivation and social isolation
enhancing the effect of depression on
mortality.32
Finally, several behavioural mechanisms could help explain the risk associated
with depression. Participants who are depressed are less likely to adhere to
their medication
regimen,7,33
affecting other illnesses they might have. They may also behave in ways that
are detrimental to their overall health, particularly
men;33 however, the
associations found in this analysis remained even after controlling for
self-care variables (smoking, alcohol, BMI). Further work is
needed to determine why the prognosis of depression appears to differ between
men and women and why it is worse among male antidepressant users.
Cause of deaths
Our results showed that the increased mortality risk associated with severe
depression in men was in part due to an increase in cardiac-related mortality,
as reported
previously.7 In
women mild but not severe depression appeared to increase cardiac death. Men
with severe depression had an increased risk of death from
unknown causes, which could reflect the helplessness of severely
depressed men, who might just give up on life and die from multiple conditions
and dwindling health. Other studies have suggested that depression and
antidepressant use increase the risk of
suicide34 and may
increase deaths by unnatural causes such as accidents, particularly among men.
However, as found in other community-based studies of older people, external
causes of death were rare in our
population.4
Limitations
This study has several limitations. The data concerning some of the
covariates were self-reported, which may be subject to recall bias with
depressed participants responding more negatively about their health. However,
as these self-report measures concern the covariates, and since similar
associations were seen in the unadjusted and adjusted analysis, it would
appear that any bias did not have a substantial influence on the results. Bias
could also be introduced from the exclusion of participants with missing data,
who were more likely to be depressed, or from the participants lost to
follow-up, who were more likely to have died. Thus, people with the strongest
potential depression–mortality association might have been selectively
excluded, so that associations between depression and mortality were
underestimated. Assessment of depression and collection of information on
antidepressant use took place at inclusion and therefore the status of these
participants at the time of their deaths is unknown. In addition, we did not
consider treatment adherance, which might have caused classification bias, or
the history and duration of antidepressant use, which might have influenced
the results. In particular, for men it would be interesting to assess whether
there was a differential effect of short-term v. long-term
antidepressant treatment on mortality. Finally, it is possible that there are
other unknown factors, including subclinical disease (in addition to that
detectable through the analysis of lipids, glycaemia and hypertension), that
might confound the association between depression and mortality.
Strengths
The study has a number of strengths. The data used in the analysis come
from a large, multicentre, population-based prospective study of people aged
65 years and over. Depression was assessed by trained staff using two distinct
measures validated in the general population, including a structured
diagnostic
interview,16,18
and antidepressant use was verified by examining the prescriptions and
medications themselves, thus minimising exposure misclassification. In
addition, by using a large community sample we were able to cover a wide range
of depression profiles, from subclinical symptoms to major depression, thus
addressing the problem of the variety of definitions of depression in previous
research. In this study we obtained comprehensive information on the mortality
status of the participants, using death registries and medical records, with
only nine participants lost to follow-up. We controlled for a large number of
covariates, particularly measures of physical health (comorbidity, physical
incapacities, recent hospitalisation, health behaviours) and cognitive
impairment, that reportedly explain in large part the reported
depression–mortality
link.13,14
Despite this, there were only minor changes in the hazard ratios between the
unadjusted and adjusted analyses, suggesting independence of associations.
Finally, in contrast to the majority of community-based studies, we have
explored the role of antidepressants in the depression–mortality
association, which enabled us to better characterise the profile of the
elderly participants who are most at risk of dying.
Our findings suggest that the relationship between depression and mortality in older populations is gender-dependent and also varies according to symptom load. This association is modified when the use of antidepressants is also taken into consideration, which indicates the importance of including this factor when investigating mortality risk. Findings from this study suggest an increased risk of mortality for men with even subclinical depression and highlight the importance of detecting depressive symptoms, most notably by the general practitioner during routine medical visits. This study suggests that inadequate treatment of late-life depression may reduce long-term survival and that resistance to treatment in men could have a detrimental effect on their survival.
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