Bidirectional mediation of evening energy proportion and chronotype on their associations with blood lipid levels in a Chinese population

The bidirectional relationship between chronotype and meal energy distribution, and the effect of their relationship on blood lipid level has not been investigated. This study aims to test and compare the bidirectional mediating effects of chronotype and meal energy distribution on blood lipid levels. Data of 9376 adult participants from 2018 wave of the China Health and Nutrition Survey (CHNS) were analysed. Two mediation models were tested and compared: one with Evening energy proportion (Evening EI%) as mediator of the association between adjusted mid-sleep time on free days (MSFa) and blood lipid levels and the other with MSFa as mediator of the association of Evening EI% with blood lipid levels. The mediating effect of Evening EI% on the association between MSFa and TC, LDL-C and non-HDL-C were significant (p < .001, p = .001, and p = .002, respectively). The mediating effect of MSFa on the association between Evening EI% and TC, LDL-C and non-HDL-C were significant (p = .006, p = .035, and p < .001 respectively). Evening EI% had a larger standardized mediation effect compared to MSFa. The bidirectional mediation effect suggests a reinforcement mechanism, in which later chronotype and higher Evening EI% reciprocally influence their negative impact on elevated blood lipid levels, leading to higher risk of cardiovascular diseases in the general population.