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Wednesday 19 February 2014

Biological Markers for Teenage Depression? Oh, please.

This week news media from around the world have been breathlessly reporting the results of a Cambridge study (Owens 2014) identifying predictive risk factors for adolescent depression.

  • "'Biological Signpost' for Teenage Depression Found" enthuses the home-town Cambridge News.
  • "Warning Sign for Depression in Teen Boys Found" says the Times of India.
  • "Saliva Test Could Help Predict Major Depression In Boys" cheers the Canadian Press.
  • "Depression Saliva Test May Reveal Those At Risk of Lifelong Mental Illness" catastrophizes the National Post (a Canadian right-wing daily founded by Conrad Black, pre-conviction).

But my personal half-witted favourite has to be:

  • "Depression May Be Diagnosed Using Spit" misunderstands State Column.

Although I must say I also like:

  • "Is your teenage boy depressed? Try the biomarker and save his life" advises Fashion Times (okay, citing this publication is perhaps a bit of shooting fish in a barrel).

Sound the trumpets! The revolution is here! The holy grail of depression - the fabled biochemical imbalance - has been found at last!

Great, but let's take two minutes to look at what the study actually shows.

It turns out that the study suggests that depression levels in young males can be identified using a combination of two markers: A hormone test and a questionnaire. Boys with high morning levels of the biochemical marker plus high scores on the questionnaire appear to be at higher risk of subsequently developing clinical-magnitude depression.  Let's consider these factors separately.

First, the questionnaire.

Remarkable. Just filling out a questionnaire can show who might be at risk for a serious psychological ailment?  By what ingenious method does this work?

It turns out that the questionnaire items ask about the presence of various symptoms of - you guessed! - depression. People who score high on such a questionnaire, indicating the presence of many symptoms but not quite enough to meet criteria for major depression, are more likely than people with few such symptoms to meet full criteria for major depression in the near future (if they're male and if they also exhibit the biochemical marker).

Excuse me? You mean the people most likely to run a fever of 103 degrees are those presently running one at 102? You mean that the people most likely to enter London in the near future are those standing in the Heathrow airport arrivals area? The people most likely to get new furniture are currently waiting in the checkout line at Ikea? Gosh!

Depression generally doesn't appear with the suddenness of a broken leg. It usually develops gradually over time, starting with transitory experiences of sadness or anxiety, building in the intensity and number of symptoms, eventually becoming what we might call subclinical depression, then mild major depression, then medium, then severe. The progression can stop at any point. Every day - every hour - our mood rises and falls. When it falls it may keep declining into major depression, but most likely it will not. But among those who eventually arrive at clinical depression they almost certainly passed through the milder depths first.

So showing that people with subclinical depression are more likely to cross the border into clinical depression than those who have no symptoms is no great surprise. Any more than showing that people in San Diego are more likely to cross the border into Tijuana than people presently watching TV in Alaska. No need for trumpets. Move along, nothing to be seen here.

What about that chemical marker?

A biochemical predictor for depression? Yikes, what could it be? A virus? A bacterium? A gene? A particular blood type?

Nope. Cortisol. A stress hormone. Groans all round.

Freak someone out and they'll have higher circulating levels of cortisol in the blood. And people under chronic stress are more likely to eventually suffer from depression.

So the revolutionary finding is that freaked-out teenage boys are more likely to get depressed than chilled-out ones. Especially if they're already showing signs of depression.

Umm, we all thought we knew that already.

One wonders whether a questionnaire asking about anxiety symptoms might have been as good a predictor as the blood cortisol level.

The real surprise in this study is that circulating cortisol did not predict subsequent depression in teen girls. There's your shocker. The headlines should have read "Common stress hormone fails to predict depression in girls" rather than trumpeting the unsurprising prediction in males. "Dropped hammer fails to reach ground" is a more interesting phenomenon than "Dropped hammer hits floor, falls over."

What am I complaining about?

Well, certainly not the researchers. Scientists the world over devote their lives to studying the minutiae of human experience, publishing their findings bit by bit in journals that few members of the public ever read. Much of the work is on fairly obvious points, and every so often common sense ideas are found to be false, sparking some genuine thought and progress. "You mean serotonin levels AREN'T any lower in depressed people? Huh! Time for a rethink!"

Sometimes one of these studies sparks interest in the popular press, and suddenly there is an avenue for describing to the world what one has been working on. These flashes of attention are unpredictable, and often it is a seemingly trivial point that does it.

A friend who studies sponges described a certain behaviour she observed as being analogous to a sneeze, for lack of a better word, and suddenly the media is interested in sponges for five minutes. The fun bits, the fascinating bits, the place of sponges within a complicated ecosystem? Nope. "Sponges Sneeze, Researcher Finds!"

So we can't fault any researcher who manages to snag some attention. There's always the chance that you can get out some genuine information along with the trivia. Kind of like stuffing medicine into the middle of a cat treat.

My problem is the media, and the level of critical analysis they bring to bear on the science they report. I have long believed that the public could develop a much clearer understanding of psychology and science by the simple expedient of never reading science reporting in the general press. The person who knows nothing is miles ahead of the one with a vast array of irrelevant half-baked misinformation.

In the case of this study we focus on an all-but-irrelevant observation and lead people to think we've made a genuine leap forward, when really the researchers have only partly confirmed (and, more significantly, partly disconfirmed) an idea that everyone familiar with the field would have suspected anyway. We are no closer to a blood (or saliva) test for depression than before this study was completed, and it says virtually nothing about what to do for these young men even if elevated cortisol is found.

Sheesh, this field. And the people who cover it. Can we get an ounce of critical thought from science reporters? Please?

Read for yourself:

Owens, M., et al. (2014). Elevated morning cortisol is a stratified population-level biomarker for major depression in boys only with high depressive symptoms. Proceedings of the National Academy of Sciences. doi: 10.1073/pnas.1318786111