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).

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.

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.

Is depression contagious?

A recent study that has been getting a lot of press coverage asserted that happiness may be contagious. This raises the question about whether depression may have a contagious element. The authors used social network theory to show that the probability of being happy was greater when other around you are happy - and found weaker effects for unhappiness. The idea of emotional contagion is a very old one, but its relevance to depressive disorders has not been confirmed. The outbreak of sports riots is another circumstance in which emotional contagion may play an important role, see here.

Stepped Care

A trend in how people are understanding optimal treatment for depression is seen in the UK NICE guidelines on depression management, which adopt a "stepped care" approach. This means that an intervention should start with a basic approach and move systematically towards more intensive treatments if the basic interventions are not successful. This fits, in theory, with the idea that many (perhaps most) episodes of depression and mild and self-limited, but that at the other end of the spectrum, many episodes are highly persistent and recurrent (link to a paper on the topic) and need long-term proactive care. This is an idea that is gaining wider acceptance in Canada, see article in the Sudbury Star.