Scientists have discovered that an imbalance of certain chemicals in the brain could help explain why teenage girls are at greater risk of depression than boys.
Specifically, researchers claimed to have identified the role of a chemical called tryptophan. Tryptophan is an essential amino acid – a building block of protein – that we get through our diets, from foods such as turkey, chicken, eggs, milk, nuts and seeds.
The body uses tryptophan to make serotonin – a brain chemical that helps regulate mood, sleep and feelings of wellbeing.
But when tryptophan is broken down in the brain, this can happen in two different ways. One option produces chemicals that are beneficial for the brain – including one called kynurenic acid – and the other produces chemicals that can damage the brain.
Scientists at King’s College London studied the blood and depression symptoms of 150 Brazilian teenagers, aged 14 to 16, to understand how these chemicals are linked to depression in boys and girls.
“Adolescence is a time when many changes occur in the brain and body, but we still know very little about the possible biological drivers for depression and how this might affect the difference between teenage boys and girls,” said senior author Prof Valeria Mondelli, Clinical Professor of Psychoneuroimmunology at King’s, in a statement.
Among teenagers diagnosed with depression or identified as high risk, the scientists found lower levels of brain-healthy kynurenic acid than those categorised as low risk, suggesting that more of their tryptophan was being broken down by producing harmful chemicals.
This association was particularly strong among girls. Depression is roughly twice as common among women than men, according to the World Health Organization (WHO), and the King’s scientists suggested that this might be one of the reasons why.
Perhaps, their study concluded, girls and women might be more vulnerable to the harmful effects of an imbalanced kynurenine pathway on the brain.
“Our study indicates the kynurenine pathway plays a role in the development of depression during the teenage years which may help us to understand why there is a higher incidence amongst girls,” said Mondelli.
The scientists also tested the young people’s blood for markers of inflammation: signs that the body might be fighting off infection, dealing with stress or coping with irritants, such as unhealthy food.
The scientists found more inflammatory markers in the blood of young people at risk of, or diagnosed with, depression, which might suggest that inflammation is driving the release of harmful chemicals in the brain.
After three years, the teenagers’ blood was tested again. The scientists found that the girls who had persistent depression had higher levels of brain-toxic chemicals compared to those who had recovered over time.
Dr Naghmeh Nikkheslat, first author of the study, said in a statement that she hoped this research could help develop support for teenagers with depression, such as medication that targeted the kynurenine pathway.
Mondelli said: “By identifying the biological pathways involved, we hope we can help build a clearer picture of how we can help teenagers manage depression.”
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