Weekly vitamin D supplementation during early infancy as a potential strategy to prevent vitamin D insufficiency: A two-center retrospective study.

Background: For preventing Vitamin D (VD) insufficiency, several VD supplementation guidelines were established worldwide. In Japan, no nationwide guidelines for preventing VD insufficiency have been implemented, whereas guidelines for preventing vitamin K (VK) deficiency-related bleeding recommend weekly supplementation of VK. The aim of this study is to clarify whether weekly VD plus VK supplementation during the early neonatal period prevents VD insufficiency at one month of age.

Methods: We retrospectively analyzed serum 25-hydroxyvitamin D (25(OH)D) levels of 555 one-month-old infants born between 2017 and 2023. Infants were classified into the control group (not supplemented), weekly group (1000 IU/week), and daily group (240 IU/day). We compared serum 25(OH)D levels among the three groups. Multivariable logistic regression analyses adjusted for formula intake and BMI were performed to better estimate the effect of VD supplementation on the prevention of VD insufficiency.

Results: We included 414, 55, and 86 infants in the control, weekly, and daily groups, respectively. All infants received weekly supplementation of VK. Serum 25(OH)D levels in the weekly and daily groups were higher than those in the control group (median (ng/mL): control 9.7 vs weekly 22.2, P < 0.001; control vs daily 23.0, P < 0.001). The frequencies of VD insufficiency were 370/414 (89.4 %), 11/55 (20.0 %), and 22/86 (25.6 %) in the control, weekly, and daily groups, respectively. Adjusted odds ratios of VD insufficiency compared to the control were 0.038 (95 % confidence intervals (95 %CI): 0.017, 0.085) and 0.036 (95 %CI: 0.019, 0.067) in the weekly and daily groups, respectively. No infant with VD excess was observed.

Conclusion: Our results demonstrated that combined weekly supplementation of VD and VK during early infancy can prevent VD insufficiency at one month of age without causing VD excess. This finding may provide evidence for the development of nationwide prophylaxis for VD insufficiency in regions lacking specific guidelines.