The changing role of family income in mental health from childhood to adolescence: findings from a UK longitudinal study.

BACKGROUND: Childhood and adolescence are critical periods of emotional and psychological development, during which socioeconomic factors such as family income may have varying effects on mental health. While previous research suggests that children from lower-income families tend to have poorer mental health outcomes, it is unclear how this association changes with age. Understanding these patterns is essential for designing interventions that target the most vulnerable periods in development. This study investigates the relationship between family income and mental health across childhood and adolescence in the UK, identifying potential age-related changes in the strength of this association. METHODS: A sample of 5667 children from the UK Millennium Cohort Study was followed from ages 3 to 17 years. Overall mental health problems, internalising and externalising problems were measured using the Strengths and Difficulties Questionnaire. Family income was assessed using inflation-adjusted annual family income, adjusted for family size and composition, and a binary indicator of poverty status. Panel data linear fixed-effects models were used to control for unobserved heterogeneity. RESULTS: Higher family income was associated with better child mental health, but the magnitude of the effect varied with age. After adjustment for confounders, lower income predicted poorer overall mental health at ages 11 and 14 years, with the strongest association observed at 14. Weak association was found at ages 3, 5, 7, and 17. A similar trend was observed for externalising problems, while the income protective effect on internalising problems showed a significant increase with age. No substantial sex differences were observed in these associations. CONCLUSIONS: Child mental health-income gradient exists in the UK and varies with age, being stronger in adolescence than childhood, and for internalising symptoms. Family income interventions/redistributions in early adolescence are more likely to reduce mental health problems in young people.