ESPE Abstracts

Introduction: Vitamin D may be considered as a hormone of prohormone of pleiotropic effects. Seasonal variability of insolation affects its synthesis in humans. In our latitude, vitamin D deficiency is widespread. In 2018, updated recommendations for vitamin D supplementation were published in Poland by Rusińska et al. In 2020, SARS-CoV-2 pandemic lockdown was introduced, with suggestions of protective anti-viral vitamin D role.

Aims to investigate the effects of: 1. seasonal variability of insolation, 2. updating guidelines of vitamin D supplementation 3. limited sun exposure during pandemic lockdown and recommendations to increase vitamin D supplementation on 25(OH)D concentrations in children.

Methods: Retrospective analysis of the long-term variability of 25(OH)D concentrations was performed in a group of 1440 children (879 boys, 561 girls) with short stature, aged 3.0-18.0 years. Concentrations of 25(OH)D were compared between the periods from mid-2014 to mid-2018 (Group A), from mid-2018 to mid-2020 (Group B) and from mid-2020 to mid-2022 (Group C). Vitamin D deficiency was defined as 25(OH)D <20 ng/ml, suboptimal supply 20-30 ng/ml. Due to the lack of normal distribution of 25(OH)D concentrations in Shapiro-Wilk test, nonparametric Kruskall-Wallis test was applied for comparisons between groups, followed by post-hoc Bonferroni-Dunn test. Next, time series regression model of seasonal variability of 25(OH)D concentrations was created.

Results: In the whole group median (25-75centile) 25(OH)D concentration was 24.0 (18.3-30.2) ng/ml, in Groups A, B and C it was 22.9 (17.3-28.7) ng/ml, 26.0 (20.0-30.7) ng/ml and 29.9 (21.3-34.3) ng/ml, respectively, with significant (P<0.05) differences between all Groups. Concentrations of 25(OH)D were normal in 26.1% children, suboptimal in 41.9%, deficient in 32.0%. Time series model including insolation in previous 3 months explained 80% of pre-pandemic seasonal variability of 25(OH)D concentrations, however during pandemy with overprediction for 1^st while underprediction for 2^nd year (that probably reflects reduced sun exposure during lockdown and increasing vitamin D supplementation).

Conclusions: Significant increase of 25(OH)D concentrations was observed both after the update of supplementation guidelines and during SARS-CoV-2 pandemic, however the scale of vitamin D deficiency and insufficiency is still too high. Seasonal vitamin D supplementation is necessary in paediatric population. Further efforts to improve the vitamin D supply in children should be taken, including updates of recommendations, as it has recently been done in Poland (Płudowski et al. 2023).