Metformin could be used to help reduce anxiety in people with type 2 diabetes following a study showing its benefits on mice.

Previous studies have found metformin, used to lower blood glucose levels in people with type 2 diabetes, may also offer benefits for other conditions such as polycystic ovary syndrome (PCOS), breast and prostate cancer, and offer neuroprotection that may reduce dementia and stroke risk.

People with diabetes have an increased risk of depression compared to those without diabetes, so French researchers set about investigating the link between anxiety, depression and insulin resistance to understand how to address all these problems simultaneously.

As a result, the University of Toulouse scientists say they have found evidence to suggest the drug can help boost levels of a brain hormone in mice fed a high calorie diet designed to make the mice insulin resistant.

The study suggested that metformin increased serotonin levels in the brain, a hormone associated with wellbeing and happiness. This led to reduced anxiety-like behaviours which the researchers referred to as “one of the most visible and early symptoms of depression”.

Metformin use reduced circulating levels of branched-chain amino acids (BCAAs) and increased serotonergic neurotransmission in the hippocampus of the brain. BCAAs are amino acids which can lower the levels of another amino acid called tryptopha, which is needed to make serotonin.

BCAAs are found in foods such as eggs, meats and dairy products. While the research suggests that a diet low in BCAAs might improve anxiety, more rigorous research would be needed to test the robustness of the finding.

Collectively, these results suggest that metformin may confer a benefit as an add-on therapy to conventional antidepressant for the comorbidity between metabolic and mental disorders. Human trials would be needed to examine whether a significant benefit is observed in humans.

The findings appear in The Journal of Neuroscience.

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