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“Mood mirror” in blood: Might its absence bring on the blues?

Low levels of a substance, acetyl-L-carnitine, in the blood are associated with depression. Could this "mood mirror" be a cure for the blues?

Stanford psychiatric researcher Natalie Rasgon, MD, PhD, and her collaborators in a multicenter study have identified a substance, acetyl-L-carnitine, whose levels in the blood of people suffering from depression are correspondingly depressed. Is the substance a mere mood mirror, or might it  be a useful tool for beating the blahs?

The study, published in the Proceedings of the National Academy of Sciences, shows that people with depression have low blood levels of acetyl-L-carnitine, which is naturally produced in the body and plays a crucial role in the metabolism of fats and energy production in each of our cells.

Although its name is admittedly a mouthful, the term "acetyl-L-carnitine" may ring strangely familiar to your ears -- in fact, maybe you're already gobbling it on a daily basis. It's a popular nutritional supplement, widely available in drugstores, supermarkets and health food catalogs.

Animal studies point to a special role for acetyl-L-carnitine in the brain, where it seems to work at least in part by preventing the excessive firing of excitatory nerve cells in brain regions called the hippocampus and frontal cortex.

In the new study, the scientists drew blood from people with histories of major depression who'd been admitted to one of two New York City medical centers during bouts of acute depression. The researchers also got blood samples from otherwise similar people with no history of depression. And, bingo: There was a substantial difference between the two groups' average blood concentrations of acetyl-L-carnitine.

On further analysis, Rasgon and her peers also found that, on average, the more severe a patient's depression was, or the earlier in life it had begun, or the more resistant to existing drug therapies it had proved, the lower the acetyl-L-carnitine level in the patient's blood was.

While these findings are certainly provocative, they don't by any means constitute proof that wolfing down a half-dozen acetyl-L-carnitine tablets is a cure for the blues. (It might also leave a fishy taste in your mouth.) Bear in mind that the investigators didn't test whether supplementing with acetyl-L-carnitine could actually improve patients' symptoms; they just took the equivalent of a snapshot.

Rasgon herself cautions against rushing to the store to pick up a bottle of acetyl-L-carnitine and self-medicating for depression. As I wrote in my news release about the study:

 'We have many previous examples of how nutritional supplements widely available over the counter and unregulated by the Food and Drug Administration -- for example, omega-3 fatty acids or various herbal substances -- are touted as panaceas for you-name-it, and then don't pan out,' she said.

But this time, the findings in people are backed up by solid animal research, and there's a coherent theoretical understanding of how an acetyl-L-carnitine deficiency could impair brain function. The key, Rasgon says, is for someone to pony up for the costly, large-scale, controlled clinical trials that could provide a definitive idea of what dose of acetyl-L-carnitine, how often, for how long is enough to clear up depression. If it does that.

Photo by Alina Miroshnichenko

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