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Vitamin D deficiency for children’s bones is 14ng, based on PTH analysis – Sept 2013

Relationship between serum 25-hydroxyvitamin D and parathyroid hormone in the search for a biochemical definition of vitamin D deficiency in children.

Pediatr Res. 2013 Sep 2. doi: 10.1038/pr.2013.139.
Atapattu N, Shaw N, Högler W.
Department of Endocrinology and Diabetes, Birmingham Children's Hospital, Birmingham, United Kingdom.

Background:Current guidelines use differing definitions of vitamin D deficiency based on serum 25-hydroxyvitamin D (25OHD) levels which complicates clinical decision making on vitamin D doses used for prevention and treatment. This study examined the natural relationship between serum 25OHD, parathyroid hormone (PTH), calcium, phosphate and alkaline phosphatase.

Methods:214 children routinely admitted without conditions affecting the natural relationship among metabolites, including 17 with radiologically confirmed vitamin D deficiency rickets, were studied. The frequency of abnormal bone metabolites was examined for different 25OHD thresholds.

Results:The best fitting intersection point where PTH levels increased was a 25OHD level of 34 nmol/l (R2 = 0.454: 95% CI 27-41 nmol/l). 73.3% and 86.1% of children demonstrated some biochemical abnormality below 25OHD levels of 41 nmol/l and 27 nmol/l, respectively. All children with rickets had 25OHD levels < 34 nmol/l. The vast majority of patients with abnormal bone metabolites had 25OHD levels < 34 nmol/l and PTH levels > 50 ng/l.

Conclusions:Vitamin D deficiency, based on PTH elevation, was best defined by a 25OHD level of < 34 nmol/l. Since deficient calcium supply often co-exists with vitamin D deficiency and both can independently cause nutritional rickets, a threshold for the skeletal effects of vitamin D should not be based purely on 25OHD levels.

PMID: 23999068

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