Background Socioeconomic inequalities in cardiovascular disease are stronger and more consistent in females compared with males. However, mechanisms underlying these inequalities and whether they emerge in early life are unclear.

Methods Trajectories of 148 metabolic trait concentrations from age 7y to 25y in a contemporary English birth cohort, The Avon Longitudinal Study of Parents and Children (ALSPAC), were analysed. Outcomes included concentrations of metabolic traits quantified using nuclear magnetic resonance spectroscopy measured at 7y, 15y, 18y and 25y. Maternal education was used as an indicator of socioeconomic position (SEP), reported by mothers at 32-weeks gestation. Using linear spline multilevel models, sex-specific associations of SEP and trajectories of each metabolic trait concentration were examined. Sex-specific associations were converted to standard deviation (SD) units by dividing the predicted total absolute difference from 7y to 25y by SEP in original units by the sex-specific SD of the trait in the reference SEP category (degree level maternal education).

Results Total participants included ranged from 5,980–6,212 with 10,023–11,945 repeated measures. SEP was associated with numerous metabolic traits trajectories in females, some which developed or strengthened by age 25y with evidence of an emerging SEP gradient. Associations were strongest for large HDL and VLDL cholesterol, apolipoprotein B/A-1 and glycoprotein acetyls. For instance, by age 25y less than O-level education was associated with 0.37 SD (95% CI: 0.21, 0.5.3), O-level with 0.28 SD (95% CI: 0.14, 0.42) and A-level with 0.08 SD (95% CI: -0.6, 0.22) higher concentrations of glycoprotein acetyls compared to degree level education. In males, associations between SEP and metabolic traits were weaker and less consistent with little evidence of an SEP gradient.

Conclusion Sex differences in socioeconomic inequalities in cardiometabolic risk appear to develop early in the life course and are evident by early adulthood with more adverse effects of SEP in females.