New information alludes to a link between lower levels of the amino acid L-Arginine and major depressive disorder (MDD). L-Arginine is used by the body to produce nitric oxide. Nitric oxide helps with increasing blood flow into the muscles. Reduced nitric oxide production may increase inflammation of the central nervous system (CNS) and oxidative stress which are believed to be involved in MDD. A key biomarker, global Arginine bioavailability ratio (GABR) is used to measure decreased L-Arginine bioavailability.
Over 350 individuals participated in this study, 99 were adults diagnosed with MDD and the rest were non-depressed controls. Blood levels of three amino acids (L-Arginine, L-Citrulline and L-Ornithine ) were measured at the onset of the study. Additionally researchers analyzed asymmetric and symmetric dimethylarginine concentrations. Both of these have both been known to inhibit nitric oxide synthase, which is an enzyme that initiates nitric oxide production from L-Arginine.
The levels of the 3 amino acids were compared between the non-depressed control and the depressed participants. Baseline levels of serum L-Arginine and GABR were reduced in patients with MDD when compared with the non-depressed control group. There was an additional follow up after eight months at which times these amino acids were again measured. Researchers looked at differences between participants with continuing depression and compared those with participants who were in “remission”. Results showed participants with depression had reduced L-Arginine bioavailability. However the participants who were in “remission” had only marginally higher levels of bio-available L-Arginine than those who continued to have depression.
Further studies are needed to determine if supplementation with the amino acid L-Arginine may help improve depression and to determine what exactly causes reduced L-Arginine bioavailability in individuals with depression.
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