People with depression have low blood levels of a substance called acetyl-L-carnitine, according to a Stanford University School of Medicine scientist and her collaborators in a multicenter study.
Naturally produced in the body, acetyl-L-carnitine is also widely available in drugstores, supermarkets and health food catalogs as a nutritional supplement. People with severe or treatment-resistant depression, or whose bouts of depression began earlier in life, have particularly low blood levels of the substance.
The findings, published online July 30 in the Proceedings of the National Academy of Sciences, build on extensive animal research. They mark the first rigorous indication that the link between acetyl-L-carnitine levels and depression may apply to people, too. And they point the way to a new class of antidepressants that could be freer of side effects and faster-acting than those in use today, and that may help patients for whom existing treatments don’t work or have stopped working.
In those studies, the animals responded to acetyl-L-carnitine supplementation within a few days. Current antidepressants, in contrast, typically take two to four weeks to kick in — in animal experiments as well as among patients.
Nasca’s animal studies suggest that acetyl-L-carnitine, a crucial mediator of fat metabolism and energy production throughout the body, plays a special role in the brain, where it works at least in part by preventing the excessive firing of excitatory nerve cells in brain regions called the hippocampus and frontal cortex.
The new study, also initiated by Nasca, recruited 20- to 70-year-old men and women who had been diagnosed with depression and, amid episodes of acute depression, had been admitted to either Weill Cornell Medicine or Mount Sinai School of Medicine, both in New York City, for treatment. These participants were screened via a detailed questionnaire and assessed clinically, and their blood samples and medical histories were taken. Twenty-eight of them were judged to have moderate depression, and 43 had severe depression.
In comparing their blood samples with those of 45 demographically matched healthy people, the depressed patients’ acetyl-L-carnitine blood levels were found to be substantially lower. These findings held true for both men and women, regardless of age.