Depressive Symptoms in Adolescence and Young Adulthood.

Importance: Depressive symptoms have increased among US adolescents since 2010. It remains unclear as to what extent this increase will persist into young adulthood, potentially turning the youth mental health crisis into a young adult mental health crisis. Objective: To test the association between birth cohort and adolescent depressive symptoms at ages 18, 19 to 20, and 21 to 22 years and changes in these symptoms by cohort. Design, Setting, and Participants: This panel cohort study analyzed data from the Monitoring the Future longitudinal survey from 1990 to 2019, including birth cohorts from 1972 to 2001. Survey respondents were recruited from US high schools in 12th grade and were approximately aged 18 years (at baseline) through age 21 to 22 years (during mail and web follow-up). Data analysis was conducted from April to October 2023. Exposure: Depressive symptoms score (>12 vs ≤12, with >12 representing top-decile scores) on a scale examining affective items (eg, "Life often seems meaningless"). Main Outcomes and Measures: High (vs lower) depressive symptoms at ages 19 to 20 years and 21 to 22 years. Results: The 36 552 respondents included 18 597 females (50.5%), and most reported having a parent who graduated from college (44.8%). Among females, 19.1% (95% CI, 16.7%-21.4%) of the most recent birth cohort (born: 1997-2001) had high depressive symptoms at age 18 years, higher than any previous birth cohort. While prevalence declined by age 21 to 22 years, it remained higher than previous cohorts at that age. Among males, 13.4% (95% CI, 11.2%-15.6%) of the most recent birth cohort had high depressive symptoms at age 18 years, and prevalence increased through young adulthood. Males with high baseline depressive symptoms had 10.24 (95% CI, 7.01-14.97) times the odds of symptoms at age 19 to 20 years and 6.20 (95% CI, 3.93-9.78) times the odds of symptoms at age 21 to 22 years. Females with high baseline depressive symptoms had 9.16 (95% CI, 6.57-12.76) times the odds of symptoms at age 19 to 20 years and 7.28 (95% CI, 4.92-10.78) times the odds of symptoms at age 21 to 22 years. The magnitude of the associations did not vary over time. Population attributable fractions indicated that the total proportion of young adult symptoms associated with depressive symptoms at age 18 years among females has increased; in the most recent birth cohort, 55.25% (95% CI, 38.11%-65.13%) of depressive symptoms at age 21 to 22 years were associated with symptoms at age 18 years. Conclusions and Relevance: This panel cohort study found that increases in depressive symptoms in adolescence persisted into young adulthood, suggesting the need for primary prevention and mental health resources during the adolescent years.