Seasonal differences in depressive affect, worry-related sleep disturbance, and low energy among UK young people

Seasonal differences in young people's mental health may be concentrated in specific symptoms. This population-based repeated cross-sectional study examined winter-non-winter differences in depressive affect, worry-related sleep disturbance and low energy among people aged 16-24 years in the United Kingdom. Understanding Society Calendar Year Datasets were analysed for 2022-2023, with extensions covering 2020-2023. Winter was defined as an interview data in December, January or February. The primary outcome was the mean of three equally weighted standardised symptom components. Standardised Pearson alpha was 0.717 and ordinal alpha was 0.737, supporting use of the index as a shared descriptive measure alongside component-level analysis. Targeted maximum likelihood estimation with Super Learner estimated covariate-standardised mean contrasts. Survey weights informed point estimation and respondent clustering informed variance estimation. Full survey-design regression and inverse-probability-of-complete-case weighting provided complementary checks. The main analysis included 5,949 person-interview observations from 4,167 young people. The winter-non-winter difference was 0.081 index points, with a 95% confidence interval from 0.029 to 0.132. On the original scales, low energy differed by 0.119 points on a 0-4 scale and depressive affect by 0.080 points on a 0-4 scale. Worry-related sleep disturbance differed by 0.044 points on a 0-3 scale, with greater uncertainty. Estimates were similar across analytical approaches and calendar periods, while winter remained at the upper end of the adjusted four-season profile. This period is for closer youth mental health monitoring and for making existing low-intensity support more visible and accessible.