Amino Acid May Be Implicated in Depression

A new Finnish study finds that people with major depressive disorder (MDD) may have reduced bioavailability of the amino acid arginine.

In the body, arginine turns into nitric oxide (NO), a powerful neurotransmitter and immune defense mediator that improves circulation and helps blood vessels relax. A person’s global arginine bioavailability ratio (GABR) is an indicator of the body’s arginine levels, and this ratio has previously been used to measure the body’s capacity to produce nitric oxide.

“It is possible that depression-induced inflammatory responses lead to reduced arginine levels. 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,” said  doctoral student Toni Ali-Sisto, lead author of the study.

The study, conducted by researchers at the University of Eastern Finland and Kuopio University Hospital, involved 99 adults diagnosed with  depressive disorder and 253 non-depressed controls.

Using participants’ fasting glucose levels, the researchers analyzed the concentrations of three amino acids: arginine, citrulline, and ornithine. This data was then used to calculate the participants’ GABRs.

The researchers also measured symmetric and asymmetric dimethylarginine concentrations, which also play a role in the production of nitric oxide. The results were then compared between the depressed and the non-depressed controls.

The study also looked at whether these concentrations changed in people with depression at an eight-month follow-up visit, and whether remission of depression had an effect on 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 says.

The findings show that participants with depression had weaker arginine bioavailability than the non-depressed controls. The study did not find significant differences in the symmetric and asymmetric dimethylarginine concentrations. The use of anti-depressants or anti-psychotics did not affect the concentrations, either.

In contrast to the researchers’ expectations, there were no clear differences in the arginine concentrations measured from people who had recovered from depression and people who remained depressed.

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

The study is published in the Journal of Affective Disorders.

Source: University of Eastern Finland