Background: Little is known about variation in vitamin B12 and folate status among Chinese women 2 years postpartum. This study assessed intake of vitamin B12 and folate and biomarkers of nutrient status among Chinese women postpartum. Methods: Demographic information, multi-/single-nutrient supplementation, dietary data, serum vitamin B12 and serum folate were assessed in 982 women within 2 years postpartum, using ten investigation sites in Zhejiang Province from the National Nutritional Study 2016–2017, which is a nationally representative cross-sectional study, to form a representative provincial sample of Zhejiang Province. The dietary diversity score (DDS) was used for assessing the dietary pattern. Results: Vitamin B12 increased slightly at the early stage of postpartum and then dropped over time. Serum folate level elevated with postpartum time. The median serum vitamin B12 concentration was 494.59 (373.21–650.20) pg/mL, and folate was 7.58 (5.02–10.34) ng/mL. Correspondingly, vitamin B12 levels suggesting marginal deficiency (200–300 pg/mL) and deficiency (<200 pg/mL) resulted as 9.27% and 3.26%, respectively, and folate level suggesting deficiency (<3 ng/mL) was 9.16%. Multi-/single-nutrient supplementation during pregnancy was associated with log-transformed serum vitamin B12 and folate level after adjusting for potential confounders (vitamin B12: ß (SE) = 0.124 (0.028), p < 0.001; folate: 0.128 (0.035), <0.001). Additionally, postpartum nutrient supplementation was associated with log-transformed serum folate level, especially for lactating women (ß (SE) = 0.204 (0.062), p = 0.001). Increased DDS was significantly associated with elevated serum vitamin B12 and folate levels (vitamin B12: ß (SE) = 0.028 (0.011), p = 0.011; folate: 0.030 (0.014), 0.031). In addition, age and educational level were influencing factors for serum vitamin B12 and folate concentrations among postpartum women. Conclusion: Serum vitamin B12 level decreased and folate level increased with postpartum age among Chinese women. Nutrient supplementation during pregnancy was related to elevated serum vitamin B12 and folate concentrations. Postpartum nutrient supplementation was associated with the increased serum folate level of lactating women. Dietary diversity was related to increased serum vitamin B12 and folate levels, especially among postpartum women with younger age and lower educational level.

Background: Adolescent obesity and depressive symptoms have increased concurrently, often presenting as co-occurrence. However, evidence on the timing of physical activity (e.g., weekday vs. weekend) and adherence to planetary health diets remains limited. This study examined these associations among adolescents in Zhejiang Province from 2022 to 2024. Methods: A total of 261,495 adolescents aged 11–18 years were included. Physical activity (PA) and dietary behaviors were assessed through the China Common Disease and Risk Factor Surveillance among Students questionnaire (reliability: Cronbach’s α = 0.84, validity: RMSEA = 0.07). The plant-based Planetary Health Diet Index (PHDI-green) adherence was defined as consuming at least one daily serving of both vegetables and fruits. Depressive symptoms were measured using the Center for Epidemiologic Studies Depression (CES-D) scale, and co-occurrence was defined as the coexistence of obesity and depressive symptoms. Temporal trends were tested using χ² tests. Sex-stratified logistic regression, restricted cubic spline analyses, and population attributable fraction (PAF) analyses were applied. Results: From 2022 to 2024, obesity (p for trend = 0.013) and depressive symptoms (p for trend = 0.003) increased significantly, while co-occurrence remained stable (p for trend = 0.058). Boys had higher obesity and co-occurrence, whereas girls showed higher depressive symptoms (all p < 0.001). Higher weekly PA, greater weekend PA and PHDI-green adherence were associated with reduced odds of obesity in both sexes (all p < 0.001). Weekend PA showed stronger associations with depressive symptoms among girls, while PHDI-green showed stronger inverse associations in boys (p for sex difference < 0.001). PAF analyses suggested that low weekend PA accounted for substantial proportions of cases (girls: obesity 10.17%, depressive symptoms 31.30%, co-occurrence 35.64%). Joint adherence to adequate PA and PHDI-green conferred the lowest odds of co-occurrence (boys: OR = 0.40, 95% CI: 0.34–0.46; girls: OR = 0.33, 95% CI: 0.26–0.43). Conclusions: Adherence to the Planetary Health Diet may be particularly relevant for boys, whereas PA—especially weekend PA—may be more strongly associated with health outcomes among girls. These findings suggest the importance of sex-specific and time-targeted behavioral strategies for obesity, depressive symptoms, and their co-occurrence in adolescents.