Relationship Between Serum 25-OH Vitamin D Levels and Secondary Hyperparathyroidism in Obese Children

Presentation Number: SUN 351
Date of Presentation: April 2nd, 2017

Michael Yuri Torchinsky*
University of Illinois College of Medicine, Peoria, IL

Abstract

Background: Low serum 25-OH vitamin D levels are more common in obese children; however, clinical implications of these findings have been unclear (1-3).

Objectives: The objective was to determine the prevalence of secondary hyperparathyroidism in obese with serum 25-OH vitamin D <20 ng/ml.

Methods: We reviewed medical records from the Pediatric Endocrine Clinic over a period of two years and identified 87 obese children aged 3 to 18 years with BMI >95 percentile, who had serum 25-OH vitamin D, intact parathyroid hormone (PTH), serum calcium, phosphorus, albumin, alkaline phosphatase, blood urea nitrogen, creatinine, and urine calcium-to-creatinine ratio measured. Sperman rank correlation coefficient was evaluated to measure association between continuous variables. Fisher’s exact test was used to assess association between categorical values.

Results: Vitamin D deficiency, defined as serum 25-OH vitamin D level <20 ng/ml, was found in 55 (63%) out of 87 obese children, including 14 (47%) out of 30 children aged 3 to 10 years, and 41 (72%) out of 57 children aged 11 to 18 years. The mean 25-OH vitamin D level decreased with age (r=-0.43, p<0.001). Only 21 (38%) out of 55 obese children with vitamin D deficiency had secondary hyperparathyroidism, defined as serum PTH level >65 ng/ml, including 4 (28%) out of 14 children aged 3 to 10 years, and 17 (41%) out of 41 children aged 11 to 18 years. Secondary hyperparathyroidism was seen in 8 (42%) out of 19 children with serum 25-OH vitamin D <15 ng/ml, and only in 13 (36%) out of 36 children with serum 25-OH vitamin D between 15 and 20 ng/ml. There was significant negative association between serum 25-OH vitamin D concentration and incidence of secondary hyperparathyroidism (p<0.001). Urine calcium-to-creatinine ratio was inversely correlated with serum PTH levels (r=-0.43, p=0.004).

Conclusions: Obese children with serum 25-OH vitamin D levels <20 ng/ml include patients who have vitamin D deficiency that adversely affects bone metabolism through secondary hyperparathyroidism and those who are vitamin D sufficient based on normal serum PTH and have low 25-OH vitamin D levels presumably due to high volume of distribution of vitamin D in excessive body fat. Measuring serum PTH in conjunction with 25-OH vitamin D may be useful to identify those obese children who can benefit most from vitamin D replacement. Increase in severity of vitamin D deficiency with age underscores the need for early screening.

 

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