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The Guardian’s bad hair day: No, cortisol in hair can’t “reveal future mental health risk” in children


2 Star

Cortisol levels in children's hair may reveal future mental health risk

Our Review Summary

bad hair dayThis story reports that in an Australian study of 70 children (average age 9.5 years), those who had experienced a higher number of traumatic events also had higher levels of the stress hormone cortisol in samples of their hair. The researchers are hypothesizing that the cortisol levels might be a marker of future mental health problems in the children, as people with depression and other mental health problems, as well as physical problems like diabetes, sometimes have high levels of cortisol.

Here’s the problem with this story: The study being reported on never actually looked at whether cortisol levels had anything to do with future mental health diagnoses. And in fact, cortisol levels were found not to be correlated with current depressive symptoms in these children. Moreover, the study had such a small sample as to make any conclusions resulting from it highly uncertain. So it’s a huge stretch to claim that cortisol in hair “may reveal future mental health risk” in children. We wish the story had been more cautious, especially in its headline, when discussing the implications of this very preliminary research.


Why This Matters

Childhood lays the foundation for one’s health over a lifetime, so identifying people who have risk factors for health problems early on — as with a simple hair test — is an attractive idea. This might allow for early intervention to modify risk and get people into treatment sooner, lessening the impact of disease or behavioral problems on their lives.


Does the story adequately discuss the costs of the intervention?

Not Satisfactory

Although the hair test is far from ready for any practical, clinical use, the story speculates that it could be a tool to identify children at risk. If it’s not too soon to make such predictions, it’s not too soon to give readers an idea of what the test might cost.

Does the story adequately quantify the benefits of the treatment/test/product/procedure?

Not Satisfactory

The magnitude of the correlation or association between cortisol and traumatic events was not mentioned, and it is very small. As per the scientific article, the history of traumatic events accounts for only 5 to 13% of the variance in the cortisol levels; the biggest effect on those levels was male or female sex, with boys having about two times higher levels than girls. So many, many other factors are influencing cortisol levels besides these reports of traumatic events.

Does the story adequately explain/quantify the harms of the intervention?

Not Satisfactory

None were mentioned. The other side of the early identification/screening coin is that labeling a child with a mental illness early on and with minimal evidence also has adverse effects with regards to self-image and development.

Does the story seem to grasp the quality of the evidence?

Not Satisfactory

The worst problem with this article is that it makes the classic mistake of jumping to the conclusion that because of the association found, the cortisol test may be used to predict future disease. This goes far beyond the data and we cringed at the headline. The sample size (14 boys and 56 girls) is far too small to even suggest this has some hope of being a diagnostic or screening test. The study authors even admit in their paper that the sample is disappointingly small and a lot more work has to be done to prove the hair-cortisol test’s veracity. The sample included mostly girls because they tended to have more hair to snip from.

We also question how good the reported history of traumatic events is, in that it is based on questionnaires to parents. As is a problem for all retrospective studies like this, memories are not perfect, and we would think that some parents would be reluctant to reveal some types of trauma such as physical abuse, witnessing of domestic abuse, and sexual abuse. There’s a big difference between those types of trauma and, for example, moving one’s home or having a skateboard accident and breaking your ankle (or worse).

Also, the scientific article notes that no correlation was found with current depressive symptoms and the hair cortisol level, which may not bode well for their overall theory that the cortisol may predict future mental health problems.

Does the story use independent sources and identify conflicts of interest?

Not Satisfactory

There are no conflicts of interest as determined from the authors’ disclosures in the published study.

But the story quotes only the first author of the study in the article, and would have done well to get opinions of the work from at least one independent source. It’s pretty unfortunate that the story did not get an outside perspective, given the nature of the article and its claims.

Does the story compare the new approach with existing alternatives?


Alternatives to testing cortisol levels in hair were mentioned — as in saliva and blood. Alternatives regarding ways to identify children at risk would seem to abound and likely explain much more than any lab test ever will. For example, kids who come from homes where they aren’t provided with adequate food, from parents with mental health problems, etc. (sociological/environmental variables). We’ll give the benefit of the doubt here but it’s really only a partial Satisfactory.

Does the story establish the availability of the treatment/test/product/procedure?

Not Satisfactory

Again, since the story speculates aggressively about the clinical usefulness of this test, we’d like to see some information about how widely available it is. Is this a highly specialized test available only to researchers? Could consumers request such tests from any lab? Such context is important to help readers understand the impact of this research.

Does the story establish the true novelty of the approach?

Not Satisfactory

The news article didn’t give any idea of how novel the research is. Apparently from the scientific article, no prior studies have tried to look at history of past traumatic events and correlate with cortisol levels. Even the hair test, as late as 2016, is described as “relatively new” by the researchers, especially in kids (hair tests for cortisol in adults go back quite a few years). Other background with regard to studies using hair and cortisol and mental illness were reviewed in the scientific article and the Guardian story might have provided a bit more background.

Does the story appear to rely solely or largely on a news release?

Not Applicable

We couldn’t find any evidence of any news release about this study. However, because there are no independent sources quoted, we can’t be sure that the story didn’t rely on such a news release that we weren’t able to find (e.g. one that may have been emailed to reporters). The best the story can score here is Not Applicable.

Total Score: 2 of 9 Satisfactory


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