"Serotonin is important in social behaviour and also play s a significant role in psychological disorders such as depression," says Professor Robert Rogers, the study's lead researcher. "We wanted to see whether serotonin activity influences the judgments we make about people's close personal relationships."
To do just that, the researchers gave two groups of volunteers drinks and then asked them to look at photographs of couples and describe how they saw them. One group had drinks that contained an amino acid called tryptophan, which helps boost the production or serotonin in the brain. The other group had tryptophan-free drinks.
The volunteers who had the ordinary drinks - that is, without tryptophan - consistently rated the couples in the photos as less intimate and less romantic than the volunteers whose serotonin levels had been boosted by tryptophan.
According to the researchers, the study's results - which are published in the journal Biological Psychiatry - suggest low serotonin levels may also change the way people perceive their own personal relationships. And that makes perfect sense as many people with mental health disorders have difficulties with romance and intimacy.
Drugs that increase serotonin levels could be the answer. There again, you could try boosting your serotonin by eating more tryptophan-rich foods, including tuna, sesame seeds, nuts, lentils and turkey.