Background: Vitamin D deficiency and dyslipidemia are prevalent in childhood, but evidence regarding their associations and the modifying role of adiposity remains inconsistent. We examined associations between serum 25(OH)D and lipid profiles and assessed whether overweight or obesity modified these associations among school-aged children in southern China. Methods This cross-sectional study was conducted from March 2023 to May 2024 in Guangzhou, China. A total of 3,067 school-aged children were included for analysis. Anthropometric measurements and socioeconomic, lifestyle, and dietary data were collected, and serum 25(OH)D, fasting glucose, and lipid concentrations were measured. Multivariable regression models and multiplicative interactions were adopted to analyze the vitamin D-lipid associations and the modification effect of ow/ob. Findings The prevalence of vitamin D deficiency and inadequacy in our cohort was 12·49% and 49·10%, respectively. Higher 25(OH)D concentrations were associated with lower TG (β= −0·026; 95% CI, −0·040 to −0·011), higher HDL-C (β= 0·025; 95% CI, 0·014 to 0·035), and lower TG/HDL-C ratios (β=−0·044; 95% CI, −0·061 to −0·027). A non-linear association was observed for HDL-C. Positive associations were also observed with TC (β=0·057; 95% CI, 0·027 to 0·087), LDL-C (β= 0·021; 95% CI, 0·000 to 0·042), and nonHDL-C (β=0·032; 95% CI, 0·007 to 0·057); however, these associations were attenuated after additional adjustment for HDL-C. No significant association was observed for the TC/HDL-C ratio. Weight-stratified analyses showed significant associations between vitamin D and lipid parameters except TC/HDL-C ratios in non-ow/ob children, while significant inverse associations in ow/ob children were confined to TG and TG/HDL-C. Significant interactions between ow/ob and 25(OH)D were initially observed for TC and nonHDL-C, but were attenuated after HDL-C adjustment. Interpretation Our study suggested that serum 25(OH)D was associated with lipid profiles in southern Chinese children, with the most consistent relationships for TG and HDL-C. Vitamin D–lipid relationships varied by adiposity and appeared partly attributable to HDL-C. Future studies are needed to clarify the causality of vitamin D-lipid associations and the role of HDL-C in vitamin D-lipid metabolism.

Background: Iron deficiency (ID) progresses through three stages: iron deficiency stores (IDS), iron deficiency erythropoiesis (IDE), and iron deficiency anemia (IDA). Neglecting subclinical ID may be harmful to school-aged children and increase the public health burden. Although diet is a key modifiable factor, most studies only focus on overall ID or merely the clinical IDA stage. This study combines a dietary index with pattern analysis to take advantage of their complementary strengths and explore their associations with ID progression. Methods: This cross-sectional study included 2493 participants from rural Guangzhou between June 2022 and May 2023. Demographic, lifestyle, anthropometric, and dietary data were collected via structured questionnaires. Blood samples were analyzed for iron status. Factor analysis identified dietary patterns, and the Chinese Dietary Guidelines Index for Children and Adolescents [CDGI(2021)-C] assessed dietary quality. We used ordinal logistic regression, multivariable logistic regression, and restricted cubic spline (RCS) models to examine dietary associations with ID stages. Results: IDS, IDE, and IDA proportions were 68.22%, 17.45%, and 14.33%, respectively. All four dietary patterns correlated positively with CDGI(2021)-C, most strongly for the fruit–vegetable (r_s = 0.552) and cereal–tuber–legume patterns (r_s = 0.386). Higher CDGI(2021)-C (OR = 0.852, 95% CI: 0.751–0.966, p-trend = 0.012), fruit–vegetable (OR = 0.866, 95%CI: 0.748–0.993, p-trend = 0.047), and meat–offal patterns (OR = 0.733, 95%CI: 0.611–0.868, p-trend < 0.001) were inversely associated with advancing ID stages, while the snack–fast food pattern was positively associated (OR = 1.233, 95% CI: 1.094–1.381, p-trend < 0.001). In IDS, higher adherence to CDGI(2021)-C, fruit–vegetable, and meat–offal patterns was associated with lower odds (all p-trend < 0.05). RCS showed nonlinear associations for the snack–fast food and cereal–tuber–legume patterns, with risk peaking at moderate-to-high adherence to these patterns (both p-nonlinear < 0.05). In IDE and IDA, the snack–fast food pattern risk rose steeply at moderate-to-high adherence (p-nonlinear = 0.036), whereas the cereal–tuber–legume pattern’s ORs fluctuated near 1 (p-nonlinear = 0.020). Conclusions: Dietary pattern and index analyses showed consistent associations across ID stages. Adherence to dietary guidelines slows ID progression, especially in early subclinical stages. More fruits, vegetables, and heme-iron-rich foods, alongside less fast food and snacks, slow ID progression. Though dietary intervention effects weaken in later stages, reducing fast food and snacks confers long-term benefits. These findings inform targeted nutrition policies to prevent ID progression in children.

Background: Childhood dyslipidemia often tracks into adulthood and contributes to early atherosclerotic changes. Although serum 25-Hydroxyvitamin D (25(OH)D) has been implicated in lipid metabolism, findings in children remain inconsistent, and whether these associations differ by overweight/obesity (ow/ob) status is unclear. We therefore aimed to investigate the associations of serum 25(OH)D concentrations and lipid profiles stratified by ow/ob status among children and adolescents aged 9–17 years. Methods: This cross-sectional study included 3067 children and adolescents from Guangzhou, southern China. Anthropometric measurements were obtained by trained staff, and ow/ob status was classified according to WHO criteria. Fasting blood samples were collected to measure serum 25(OH)D and lipid parameters. Multivariable regression analyses were adopted to determine the associations between serum 25(OH)D and lipid profiles. Stratified analysis and interaction tests were further applied according to ow/ob status. Results: Higher 25(OH)D concentrations were most consistently associated with lower TG (β = −0.026; 95% CI, −0.040 to −0.011), higher HDL-C (β = 0.025; 95% CI, 0.014 to 0.035), and lower TG/HDL-C ratios (β = −0.044; 95% CI, −0.061 to −0.027). Positive associations were also observed for TC, LDL-C, and non-HDL-C with serum 25(OH)D, but these were attenuated after further adjustment for HDL-C. No significant association was observed for the TC/HDL-C ratio. In stratified analyses, associations with several lipid parameters were observed mainly among children and adolescents without ow/ob, whereas significant inverse associations among those with ow/ob were largely limited to TG and the TG/HDL-C ratio. Significant interactions between vitamin D and ow/ob status were observed for TC and non-HDL-C, but were attenuated after further adjustment for HDL-C. Conclusions: In this cross-sectional study, serum 25(OH)D was associated with several lipid parameters among children and adolescents, most consistently with TG, HDL-C, and the TG/HDL-C ratios. Stratified analyses showed different vitamin D–lipid association patterns across ow/ob status, with statistically significant interactions observed only for TC and non-HDL-C. The attenuation of several associations after adjustment for HDL-C suggests that HDL-C may be involved in these observed patterns. Future longitudinal studies are needed to examine causality of vitamin D–lipid associations and the potential role of HDL-C in these associations.