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Thursday, December 31, 2009

Antidepressants and Risk of Stroke

The December issue of the Archives of Internal Medicine contains a paper based on the Women's Health Initiative dataset (a large cohort of community dwelling women aged 50-79 in the US) that describes a possible association between antidepressant use and stroke (link to abstract). Hemmorhagic stroke (strokes caused by bleeding in the brain) seemed to account for most of the association. The authors also looked for an association between antidepressant use and coronary heart disease - finding no association. This report may cause some alarm for people taking antidepressant medications, but it is important (in my view) to consider three factors when interpreting these results. First, depression itself is associated with cardiovascular disease, so studies such as this one are vulnerable to "confounding by indication" - a situation where the reason for use of a medication causes a problem that subsequently seems to be due to the medication itself. The study used sophisticated means to control for confounding by indication, but even the most sophisticated approaches are not always effective for controlling this type of bias. Second, this is not the first study to look at this possibility, and the literature as a whole has been inconsistent. On the other hand, some antidepressants are known to increase the risk of bleeding related complications, so what is being reported is biologically plausible. The risk-benefit trade-offs for antidepressant use need to be better delineated so that people can make informed decisions about depression treatment - this study is an example of one that is pursuing this goal. The risks and benefits may play out differently in people with severe depression and/or other risk factors for stroke - hopefully, research in this area will remain active until these issues are decisively resolved.

Friday, December 25, 2009

Depression and Employment Status

We've recently been looking at the impact of depression on employment status in Canadians using longitudinal data from the National Population Health Survey. We felt that this was important since, although it is well known that unemployment and depression are associated, it is possible both that unemployment could cause depression and that depression could cause unemployment. We were particularly interested in looking at the latter question. We selected people who were all working at baseline, divided these into groups that experienced (or did not) an episode of major depression. The effect of depression was greatest in young people - perhaps reflecting the greater difficulties faced by younger people in coping with depression, or their greater vulnerability to its effects (for example, because they may be less well-established in their career). However, it is also possible that older people who were working at baseline represented a subset of those who were more effective at coping with the symptoms - ie. those whose careers had been interrupted by depression prior to the baseline interview (1994) would not have been eligible, a selective effect that may have occurred less often in the younger respondents.

The results are published in the Canadian Journal of Psychiatry, here.

Tuesday, November 10, 2009

Another blogger interested in depression

Another blog about depression has just added a list of 10 myths about the condition. Here is the link.

Sunday, October 25, 2009

Cohort Effects in Major Depression

Since psychiatric epidemiologic surveys began being conducted in the 1980s a strange pattern has been seen in one of the commonly estimated parameters: lifetime prevalence (LTP). LTP refers to the proportion of a sample who report having major depression during their prior lifetime. Since older people have had longer lives and a greater chance of becoming depressed, intuition suggests that LTP should increase with age. In contrast, most studies have found that it increases in young adult life and then declines subsequently with age (see September posting to this blog). There are a variety of possible explanations: (1) that the first onset of of depression occurs commonly in young people but that this incidence declines with age - this could explain the flattening of an age specific prevalence curve - but not a decline, (2) higher mortality in people with depression, (3) recall bias- ie. people forgetting about, or reframing, their experience of depression when they were young as they get older. These explanations have largely been ignored, however, and most researchers have instead claimed that more recent birth cohorts (those of younger age in surveys) have a higher risk of depression. We have developed some simulations to assess these explanations - and (as noted below) have confirmed that a cohort effect is not a necessary or likely explanation. The other factors can explain the observed pattern, the simulations may be accessed here. If the pattern is due to a cohort effect, however, this will lead to a 10-fold increase in depression lifetime prevalence in elderly people in upcoming decades, a dynamic depicted here.

Saturday, September 5, 2009

Major Depression Epidemiology

The biggest project in psychiatric epidemiology lately is the World Mental Health Survey initiative, which is conducting standardized surveys in more than 30 different countries. A remarkable thing about these surveys is that almost all of the authors from each participating country have concluded that there is a cohort effect for major depression. The standardized interviews (the CIDI, version 3.0) all inquire about lifetime history of specific disorders. One expects that as people get older and have a longer time at risk, the frequency of a positive lifetime history would increase - but this doesn't happen. Instead, the lifetime history starts to decrease in middle age. The idea of a cohort effect is an interpretation of this finding - with the interpretation being that people born more recently (younger at the time of the survey) are at higher risk of depression and this means that there will be an increase in depression in older age groups as these recent birth cohorts age. However, there are other possible explanations - differential mortality (people with depression may die more often as they get older) and recall bias (people may forget about past episodes, or reframe those experiences, so they come out as lifetime negative later in life when they would have come out as positive had they been interviewed earlier). I have been looking at these issues in simulation models, and have produced a brief video showing the results, click here and follow the link to "view." As it turns out, expected levels of forgetting/reframing of past episodes can easily explain the observed pattern. There is no reason to suppose that a cohort effect will lead to higher rates of depression in the future.

Saturday, August 8, 2009

Smoking and Depression

Traditionally, the risk factors that have recieved most attention in research about depression are psychosocial factors such as cognitive style and loss events. An exception to this rule is the emphasis that has been placed upon the role of genes in etiology. However, over the years, many studies have suggested that there is a strong association between smoking and depression. There are several possible explanations: one possibility is that people with depression may use nicotine to self-medication their symptoms. Another possibility is that smoking is a risk factor for depression, or their may be shared risk factors for both things. A PhD student at the University of Calgary has recently confirmed the existence of a strong association in the Canadian population, see here.

Thursday, May 7, 2009

Consensus Statement on Depression

This is a consensus statement on what to do about depression in Canada.
It is the summary output of a conference that was held last year.
The report is not just an academic report, it had lots of diverse input.

You can get a copy of the report here.

Is Depression Much More Common than Experts Think?

Standardized interviews to detect depression have been available since the 1980s. In order to determine the prevalence of major depression, most studies have adminstered these interviews to samples of people in the community. There is, however, a potentially serious problem with this approach. Not all episodes of depression are necessarily remembered. Furthermore, the instruments attempt to identifiy episodes by asking about specific symptoms, but people may not remember, for example, a series of weeks during which their sleep or appetite patterns were altered. Furthermore, of course, peoples' memories of events can change over time. The end result is that the prevalence of major depression in the population may be seriously underestimated. To explore this possibility, I recently examined the accumulation of depressive episodes during 14 years of follow-up in the National Population Health Survey. Since the participants in this cohort were interviewed every two years, they were probably much more likely to have episodes detected than other studies where they have been asked to recall episodes occuring much earlier in their life.

The hypothesis was confimed: the prevalence of depression as measured by the prospective approach was twice the usually cited figures for Canada. Major depression is probably much more common than is currently beleived. Details (in preliminary form) may be found here in the journal BMC Psychiatry.

Depression and Participation in Preventive Health Care Activities

Prevention plays an important role in health care. Monitoring blood pressure is a way to detect elevated blood pressure and by treating this prevent strokes and heart disease. Procedures such as mammography and Pap tests can detect cancers earlier than they would normally be detected and at a stage when they are more likely to be curable. When people are struggling with depression they may be less likely to persevere with these kinds of preventive activities. Even mild depression can affect peoples' energy and motivation, which could have an impact. Also, while depressed, it is more difficult for people to think positively - and preventive health care is all about creating a healthier future. Finally, when people are severely depressed they may not value their life as much (the most extreme such manifestation being suicidality) and therefore not take steps to safeguard it.

Because of these concerns, we have examined the impact of major depression on participation in preventive health care activities in Canadians during the late 1990s and up to 2004. The results are available here. Surprisingly, no effect was found. The most likely explanation is that even though depression might cause reduced participation, this is offset by more frequenty contact with the health system. People with depression contact the health system more often because they are seeking or receiving treatment, and perhaps for other reasons as well (e.g. a tendency of depression to magnify pain complaints).

Wednesday, April 22, 2009

Does depression contribute to high blood pressure?

According to population surveys, large number of medical conditions are associated with major depression. One of these is high blood pressure (hypertension). It is possible that being diagnosed with high blood pressure would lead to depression because receiving such a diagnosis may be a stressful even for some people. However, it is also possible that depression might increase the risk of high blood pressure. There are several mechanisms by which this might occur. One is that depression is characterized by activation of the autonomic nervous system, which is involved in the regulation of blood pressure. Another possibility is that immune activation, which occurs in depression, may lead to blood pressure changes. We recently used a Canadian health data source (a study called the NPHS) to explore the possibility that people with major depression would be more likely develop high blood pressure. The hypothesis was confirmed: an increased risk of high blood pressure was observed, see PubMed link. This does not necessarily mean that depression was causing high blood pressure. Another possibility is that there is a shared cause of both conditions. Nevertheless, people with major depression should be aware that they may be at higher risk and closer monitoring of their blood pressure may be warranted.

Monday, January 26, 2009

Immune Function, Allergies, and Depression

Traditionally, there has been concern that depression may be associated with diminished immune function, such that people who are depressed may be more vulnerable to infectious diseases.

However, in recent years there has been increasing evidence of immune activation (e.g. higher levels of markers of inflammation in peripheral blood) in people who are depressed. It has been hypothesized that immune activation in depression may be a mechanism by which depression causes cardiovascular disease and increases mortality in cardiovascular disease. These observations dovetail with reports that certain immune modulators (particularly interferons), when used in the treatment of hepatitis C and malignant melanoma may trigger depression, and that antidepressants may prevent this from happening.

These possibilities cast new interest on the observation that allergies may be associated with depression. After all, allergies represent an immunologic "over response" to an environmental stimulaus. Unfortunately, the existing reports have been inadequate to explore this possibility. We have looked at this in a Canadian cohort in a recently published study and found that people with clinical depression have a higher risk of developing allergies. A full report can be found here.