Tryptophan: Study finds teen girls more prone to depression than boys due to chemical imbalance

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 claim to have identified the role of a chemical called tryptophan. Tryptophan is an essential amino acid, a building block of protein that we obtain through our diets, particularly from foods, such as turkey, chicken, eggs, milk, nuts, and seeds.

Researchers highlight that the body uses tryptophan to produce serotonin, a brain chemical that helps regulate mood, sleep, and feelings of well-being.

However, when tryptophan is broken down in the brain, it can happen in two different ways. One pathway produces chemicals that are beneficial for the brain, including one called kynurenic acid, while 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 Professor Valeria Mondelli, Clinical Professor of Psychoneuroimmunology at King’s College London.

Among teenagers diagnosed with depression or identified as high-risk, the scientists found lower levels of brain-healthy kynurenic acid compared to those categorised as low-risk, suggesting that more of their tryptophan was being broken down into harmful chemicals.

This association was particularly strong among girls. Depression is roughly twice as common among women as men, according to the World Health Organisation (WHO), and the King’s College scientists suggested that this might be one of the reasons why.

Perhaps, the study concluded, girls and women might be more vulnerable to the harmful effects of an imbalanced kynurenine pathway in the brain.

“Our study indicates that the kynurenine pathway plays a role in the development of depression during the teenage years, which may help us understand why there is a higher incidence among girls,” said Mondelli.

The scientists also tested the teenagers’ blood for markers of inflammation, which are 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 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 added, “By identifying the biological pathways involved, we hope we can help build a clearer picture of how we can help teenagers manage depression.”

Adolescence is the time of life between childhood and adulthood. During this period, many changes take place, including some differences between boys and girls. In general, depression rates are higher, and self-esteem is lower in girls when compared with boys during adolescence.

The characteristics of adolescence in both boys and girls include rapid growth and biological changes, heightened awareness of one’s appearance, sexual attraction, cognitive development, career consciousness, and other new and exciting changes in various areas.

Other changes that occur in the body during adolescence include a physical growth spurt. These changes involve an increase in height, growth of pubic and underarm hair, and skin changes. Hormonal changes are also experienced, with notable increases in estrogen for females and testosterone for males, which contribute to the onset of puberty.