Maternal Vitamin D Status at Delivery and Allergic Outcomes in Early Adolescence: Prospective Findings from the KLOTHO Birth Cohort

Background: Prenatal vitamin D exposure has been proposed as a potential determinant of immune development and subsequent allergic disease risk in offspring; however, long-term cohort data remain inconsistent. Methods: We analyzed data from the KLOTHO birth cohort, including 98 adolescents with available allergic outcome assessment. A maternal–neonatal sub-cohort of mother–child pairs with available maternal and neonatal serum total 25-hydroxyvitamin D3 [25(OH)D] measurements at delivery was used for vitamin D analyses. Allergic outcomes included asthma, allergic rhinitis, and eczema in offspring. Associations were evaluated using descriptive statistics, Spearman correlation analyses, and logistic regression models. Results: Maternal 25(OH)D concentrations were not significantly associated with asthma (ρ = 0.075, p = 0.652), allergic rhinitis (ρ = 0.100, p = 0.556), or eczema (ρ = 0.131, p = 0.426). In crude logistic regression models, vitamin D concentrations were not associated with asthma (odds ratio (OR) per 10 nmol/L: 1.07, 95% confidence interval (CI): 0.78–1.48, p = 0.67), allergic rhinitis (OR: 1.05, 95% CI: 0.76–1.45, p = 0.77), or eczema (OR: 1.17, 95% CI: 0.86–1.60, p = 0.31). Adjusted models including maternal age, pre-pregnancy body mass index (BMI), season of delivery, and ultraviolet exposure yielded similar non-significant findings, although analyses were limited by a reduced complete-case sample size. Conclusions: In this prospective cohort with follow-up into early adolescence, vitamin D status at delivery was not associated with asthma, allergic rhinitis, or eczema in offspring. These findings support a lack of statistically significant association; however, potential non-linear relationships should be interpreted cautiously, given the modest sample size.