Influence of deficiency or insufficiency of vitamin D on the circadian rhythm of serum calcium level

Background: mild hypocalcemia is a common laboratory finding that is not accompanied by the clinical symptoms. The most common causes of hypocalcemia are inadequate calcium intake and vitamin D deficiency. Given the high prevalence of vitamin D deficiency (insufficiency), it seems relevant to determine the daily variability of serum calcium levels before and after its supplementation.Aims: to assess the effect of 25(OH) vitamin D level on the daily profile of serum calcium and 24-hour urinary calcium levels. MATERIALS AND METHODS: the interventional, prospective, comparative study of 10 healthy volunteers (women/men - 9/1) was performed. We have analyzed the daily profiles of serum calcium and 24-hour urinary calcium levels. Summary duration of this study was 8 months and consisted two hospitalizations. Statistical analysis was done on August 2020. The descriptive statistics are represented by medians and the first and third quartiles in Me (Q1; Q3), average, maximum, and minimum values M (min; max) and by absolute and relative frequencies.Results: Me serum calcium levels (Catotaland Cacorr.) and 24-hour urinary calcium levels did not differ before and after vitamin D supplementation. However, the number of reference calcium values increased as 25 (OH) vitamin D level was reached more than 30 ng/ml from 90.8% to 100% for Catotal and from 94.2% to 97.5% for Cacorr. Episodes of hypocalcemia were registered in patients with low vitamin D levels: in 3.33% of cases according to Catotal and 5.8% for Cacorr. The frequency of hypocalcemia decreased for Catotal (to 0%) and for Cacorr. (to 2.5%) after treatment with cholecalciferol. Analysis of Catotal and Cacorr. deviations during the day showed a less variability of the calcium profile after treatment, This study also revealed circadian character of daily serum calcium profile with the presence of maximum (09:40-17:40) and minimum (23:40-07:40) values during the day.Conclusions: Our study demonstrated the improvement of daily serum calcium profile after vitamin D supplementation. We confirmed the increased number of reference calcium values, decreased variability of serum calcium levels during the day and decreased frequency of hypocalcemia