Another blogger interested in depression

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

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.

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.

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.

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).