A New Study Has Unearthed A Clue About Why Treatment-Resistant Depression Happens

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There are many different types of depression, and one of the most severe is known as treatment-resistant depression. This kind of depression doesn't respond well to traditional treatments, like antidepressants, psychotherapy, or cognitive behavioral therapy, according to the Mayo Clinic. It can be a long, difficult process to find a treatment that can give people with this kind of depression relief from their symptoms. Treatment-resistant depression, according to research from Harvard University, occurs in around three in 10 adults with depressive symptoms, who can't find effective treatment after years of trying. And now, a new study suggests that treatment-resistant depression might be linked with levels of one single molecule. That's right — just one molecule.

The study, published in the Proceedings of the National Academy of Sciences, found that there's some sort of relationship in humans between depression and a molecule called acetyl-L-carnitine, which is a kind of amino acid that helps the expression of genes, particularly ones related to neurotransmitters in the brain. The amino acid is naturally produced by the body, but can also be purchased as a supplement. In the past, the molecule has actually been used to help age or disease-related brain degeneration and memory loss, so we already knew that it has a good relationship with brain health. The new study, though, shows that this relationship may also go the other way.

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The researchers found that in people with major depressive disorder, levels of acetyl-L-carnitine, as measured through blood samples, were much lower than they were in people without depression. Coincidence? Probably not. And there's more. The study also found that there was a relationship between low levels of the molecule in blood and getting treatment-resistant depression; the lower the acetyl-L-carnitine levels, the more severe the depression and the less likely antidepressants had helped.

Interestingly, this discovery has particular resonance for women. The scientists found that, in female patients, having low levels of the molecule was a particularly accurate indicator of treatment-resistant depression. It's not at all clear why this is the case, but it's an important discovery that marks out a particular kind of serious depression in women as potentially unique.

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So why does this matter so much? Low levels of this one nutrient can have far-reaching effects. The scientists behind the study want the blood test for acetyl-L-carnitine to be used early on in diagnosis, as a "biomarker" for depression. That way, people who have depression that might resist treatment can discover that issue early in their GP's office, without wasting months and years trying methods that won't work.

The good news for people with treatment-resistant depression is that there's hope for new avenues of treatment. Studies have shown there's a lot of potential for ketamine to help people who haven't seen results with any other antidepressant or treatment. More research needs to be done to determine how exactly depression affects the levels of this nutrient, but it's pretty clear that the absence of acetyl-L-carnitine is something that merits attention. Hopefully, one day treatment-resistant depression can be diagnosed with a simple pinprick, rather than through painful trial and error.