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Effect of short-term hyperthyroxinemia on vitamin D metabolism in congenital hypothyroidism
1Pediatric Nephrology Unit, Chaim Sheba Medical Center, Tel Hashomer, Sackler School of Medicine, Tel Aviv University, Israel.
Insights
Children with congenital hypothyroidism on L-thyroxine therapy showed increased 1,25-dihydroxyvitamin D levels after a dosage increase. This vitamin D metabolite change was linked to higher urinary calcium excretion.
Area of Science:
- Pediatric Endocrinology
- Nutritional Biochemistry
- Calcium Metabolism
Background:
- Congenital hypothyroidism requires L-thyroxine treatment.
- Vitamin D metabolite status in treated children is not fully understood.
- Thyroid hormone influences vitamin D metabolism.
Purpose of the Study:
- To investigate the effect of short-term L-thyroxine dosage increase on vitamin D metabolite concentrations in children with congenital hypothyroidism.
- To assess the relationship between altered vitamin D metabolites and urinary calcium excretion.
- To compare findings with adult data.
Main Methods:
- Measurement of serum vitamin D metabolites (25-hydroxyvitamin D, 24,25-dihydroxyvitamin D, 1,25-dihydroxyvitamin D) in nine children.
- Analysis before and after a 33% increase in L-thyroxine dosage for three weeks.
- Monitoring of urinary calcium excretion, serum calcium, phosphorus, and parathyroid hormone levels.
Main Results:
- Serum concentrations of 25-hydroxyvitamin D and 24,25-dihydroxyvitamin D remained unchanged.
- A significant increase in 1,25-dihydroxyvitamin D was observed after hyperthyroxinemia.
- Increased urinary calcium excretion correlated with higher 1,25-dihydroxyvitamin D levels.
- No significant changes in serum calcium, phosphorus, or parathyroid hormone explained the 1,25-dihydroxyvitamin D increase.
Conclusions:
- Short-term L-thyroxine dosage increase in children with congenital hypothyroidism elevates 1,25-dihydroxyvitamin D.
- This elevation is associated with increased urinary calcium excretion.
- The observed effects in children differ from those reported in adult studies.
Abstract:
The circulating concentrations of vitamin D metabolites were measured in nine children (four to ten years of age) with congenital hypothyroidism on L-thyroxine therapy, before and after a short term increase (33%) in dosage. The concentrations of 25-hydroxyvitamin D and 24,25-dihydroxyvitamin D were not altered, but the concentration of 1,25 dihydroxyvitamin D was significantly higher in the serum of the children after three weeks of hyperthyroxinemia. This was associated with an increase in urinary calcium excretion. The increases in serum concentration of 1,25 dihydroxyvitamin D cannot be explained by differences in serum levels of calcium, phosphorus or parathyroid hormone. These findings differ from data obtained in adults.