Impact of COVID-19-Related Social Restrictions on Vitamin D Levels in Japanese Newborns and Infants: A Retrospective Cohort Study.

This study evaluated the impact of the COVID-19 pandemic on vitamin D status in Japanese newborns and early infants by comparing serum 25-hydroxyvitamin D (25(OH)D) concentrations between pandemic and non-pandemic periods. A total of 805 newborns aged ≤4 days and 366 infants aged 29-42 days were included. Nearest-neighbor matching was performed to adjust for key confounders, including season, body mass index, and formula intake. No significant differences in serum 25(OH)D levels were observed between the overall pandemic and non-pandemic periods in either age group after matching. In the ≤4-day-old group, median [IQR] 25(OH)D concentrations were 15.2 [11.9-18.9] ng/mL and 14.9 [12.1-18.9] ng/mL in the pandemic and non-pandemic groups, respectively (P = 0.79). In the 1-month-old group, corresponding values were 12.2 [6.8-17.2] ng/mL and 12.6 [6.2-17.9] ng/mL (P = 0.70). When the analysis in the 1-month-old group was restricted to the strict restriction period corresponding to the state of emergency, serum 25(OH)D levels were significantly lower before matching (P = 0.005), but the difference was no longer significant after matching (P = 0.12). Across all analyses, markers of bone metabolism, including calcium, phosphorus, alkaline phosphatase, and intact parathyroid hormone, showed no clinically meaningful differences.In addition, vitamin D insufficiency (<20 ng/mL) was highly prevalent in both age groups, regardless of the pandemic period. These findings suggest that COVID-19-related restrictions had a limited impact on vitamin D status in Japanese newborns and early infants, although potential effects during periods of strict social restrictions cannot be excluded.