An estimated 280 million people worldwide suffer from depression, a condition influenced by a complex interplay of social, psychological and biological factors. Those who have experienced adversities such as unemployment, loss or trauma are at higher risk. A comprehensive review, from 2001 to 2020, revealed that 34 per cent of adolescents aged between 10 and 19 reported elevated depressive symptoms globally, with the Middle East, Africa and Asia showing the highest prevalence. Notably, female adolescents exhibited a higher prevalence than males.
Depression in adolescents stems from various factors including genetics, environment and social circumstances. A recent study in JAMA Psychiatry delved into a novel link between prenatal maternal inflammation and depressive symptoms in adolescent offspring. The research, examining 674 mother-offspring pairs, focused on those who received obstetric care from June 1959 to September 1966. This study unveiled sex-specific pathways from prenatal maternal inflammation to adolescent depressive symptoms.
Data on pregnancy and blood sera were collected from mothers, with psychiatric symptom data gathered from offspring during childhood (ages 9-11 years) and adolescence (ages 15-17 years). Maternal prenatal inflammatory biomarkers, indicative of inflammation during pregnancy, were assessed during the first and/or second trimesters. These biomarkers, measurable in blood or other bodily fluids, offer insights into the presence and severity of inflammation in the body. Maternal inflammation during pregnancy has previously been linked to adverse neurodevelopmental outcomes in offspring, such as autism spectrum disorder, attention deficit hyperactivity disorder and Tourette syndrome.
The study revealed a significant association between higher levels of interleukin 6 (IL-6), a specific type of inflammation, during the second trimester of pregnancy and increased depressive symptoms in adolescent offspring. Notably, in male offspring, the analysis indicated that childhood externalising symptoms played a significant mediating role in the link between IL-6 levels in the first trimester and adolescent depressive symptoms. Childhood externalising symptoms encompass a range of problematic behaviours directed outwardly towards others or the social environment, including hyperactivity, impulsivity, aggression and rule-breaking. The observation suggested that the impact of maternal inflammation on offspring depressive symptoms is influenced by the child's behaviour during childhood and the timing of maternal inflammation during pregnancy. In female offspring, it was observed that childhood internalising symptoms mediated the link between second-trimester IL-1Ra (natural anti-inflammatory factor) levels and adolescent depressive symptoms. Childhood internalising symptoms encompass various emotional and psychological challenges directed inwardly towards the individual, including anxiety, somatic complaints and withdrawal.
These findings indicate that the influence of maternal inflammation on offspring depressive symptoms is shaped by the child's gender and the timing of maternal inflammation during pregnancy.