People might have major depressive disorder because of reduced levels of amino acid found in blood samples, according to a study in Finland. Photo by KieferPix/Shutterstock

Feb. 21 (UPI) -- Reduced levels of an amino acid found in blood samples have been linked to major depressive disorder, according to a new study in Finland.

Researchers with the University of Eastern Finland and Kuopio University Hospital studied 99 adults aged 20-71 with diagnosed major depressive disorder and 253 non-depressed control adults in a report published Wednesday in the Journal of Affective Disorders.


The body uses the amino acid arginine to produce nitric oxide, which is a mediator for the nervous system and immune defender, and plays a role in vascular regulation. Reduced arginine is also a known risk factor of cardiovascular diseases.

"It is possible that depression-induced inflammatory responses lead to reduced arginine levels," doctoral student Toni Ali-Sisto, the lead author of the study, said in a release. "This may result in insufficient production of nitric oxide for the needs of the nervous system and circulation. However, we don't know yet what exactly causes reduced arginine bioavailability in people with depression."

Researchers analyzed three amino acids -- arginine, citrulline and ornithine -- from participants' fasting glucose samples. In addition, symmetric and asymmetric dimethylarginine concentrations were also measured from the serum. This data was used to calculate their global arginine bioavailability ratio.

No significant differences were found in the symmetric and asymmetric dimethylarginine concentrations between the two groups.

Researchers also analyzed samples taken eight months later.

Anti-depressants or anti-psychotics did not affect the concentrations.

"Although our study shows that people with depression have reduced arginine bioavailability, this doesn't mean that taking an arginine supplement would protect against depression. That's an area for further research," Ali-Sisto said.

And there were no significant differences between people who remained depressed and those who had recovered.

"Arginine bioavailability was slightly higher in people who had recovered from depression than in people who remained depressed," Ali-Sisto said. "However, a more extensive set of data and a longer follow-up period are necessary for estimating arginine's role in depression recovery."