A drug given to millions of people to treat their diabetes could alleviate anxiety, research suggests.
Tests on mice showed those given metformin showed less signs of anxiety-like behaviour.
Scientists believe the drug increases levels of serotonin, known as a feel-good chemical, in the brain.
Serotonin is produced in the brain and contributes to the feeling of happiness and relaxation, among other bodily functions.
Metformin used to treat diabetes was able to alleviate anxiety in a study on mice by increasing levels of the feel-good chemical in the brain, a study has shown
The team, led by Dr Bruno Guiard from Research Center on Animal Cognition in Toulouse, France, raised mice on a high fat diet.
They showed insulin resistance – a hallmark of type 2 diabetes – and depression symptoms including anxiety and despair.
Diabetics are known to be at an increased risk for disorders such as depression, thought to be due to having lower levels of serotonin.
The neurotransmitter, which affects mood, creates messages between nerve cells throughout the body, mostly influencing the brain.
It is created by the conversion of the amino acid tryptophan – a building block of protein – and an enzyme called tryptophan hydroxylase.
Tryptophan is one of the essential amino acids humans need. However, the body cannot synthesize it and so it has to be obtained from the diet.
Previous studies have found patients and rodents with type 2 diabetes have low levels of circulating tryptophan.
As well as this, tryptophans route to the brain where it converts to serotonin is blocked because of a build-up of a different amino acid (BCAAs).
The study showed metformin can curb the amino acids, called branched chained amino acids (BCAAs).
Writing in their paper, the researchers said metformin stimulated and improved the transmission of serotonin in the hippocampus.
The hippocampus is responsible for long term memory and emotional response, and its functions and size have been found to be altered in those with major depression.
The researchers achieved similar effects by reducing the amount of BCAAs in the diet.
Amino acids are essential for the body to function and BCAAs can only be obtained from food such as eggs, meat and dairy products.
As well as finding metformin may help, Dr Guiard and colleagues said the findings suggest a diet poor in BCAAs ‘could help relieve depressive symptoms’.
The relationship between diabetes and mental health disorders such as depression and anxiety aren’t fully understood and could trigger one another.
The stress of managing diabetes can cause feelings of depression. While depression can lead to poor lifestyle choices that lead to obesity, a cause of type 2 diabetes.
Anxiety disorders are the most common mental illness in the US, affecting 18.1 per cent of the adult population every year, according to Anxiety and Depression Association of America.
In the UK, general anxiety disorder is estimated to affect up to five per cent of the population, according to the NHS.
