Linear growth in relation to the circulating concentrations of insulin-like growth factor I, parathyroid hormone, and 25-hydroxy vitamin D in children with nutritional rickets before and after treatment: endocrine adaptation to vitamin D deficiency

Abstract

The objective of the study was to determine the degree of linear growth retardation of patients with vitamin D deficiency rickets at presentation and the magnitude of catch-up growth in relation to their calcium (Ca) homeostasis and hormones affecting it before and after treatment. This prospective study recorded the anthropometric data and measured the circulating 25-hydroxy vitamin D (25-OH-D), insulin-like growth factor I (IGF-I), parathyroid hormone, Ca, phosphate, and alkaline phosphatase concentrations in 46 infants and children with nutritional (vitamin D deficiency) rickets before and 6 months or more after treatment with one intramuscular injection of vitamin D3 megadose (300 000 IU). Forty normal age- and sex-matched children were included as controls for the auxological data. At presentation, patients' mean age = 13.1 ± 1.1 months, length standard deviation scores (LSDS) = −1.5 ± 0.2, and body mass index = 16.3 ± 0.85. They were significantly shorter and had markedly lower growth velocity standard deviation scores (GVSDS) compared with normal controls (LSDS = 0.25 ± 0.18 and 0.31 ± 0.22, respectively). Six months after treatment, the LSDS increased significantly in patients to −0.45 ± 0.13, with a significantly increased GVSDS (2.76 ± 0.45) and body mass index (16.9 ± 0.65). They were still shorter but with significantly higher GVSDS compared with normal controls. Serum Ca and phosphate concentrations increased from 2.07 ± 0.25 and 1.23 ± 0.24 mmol/L, respectively, before treatment to 2.44 ± 0.2 and 1.94 ± 0.2 mmol/L, respectively, after treatment. Serum alkaline phosphatase and parathyroid hormone concentrations decreased from 1183 ± 219 U/L and 294 ± 87 pg/mL, respectively, before treatment to 334 ± 75 U/L and 35.2 ± 15.2 pg/mL, respectively, after treatment. The 25-OH-D level increased from 4.5 ± 0.56 ng/mL before treatment to 44.5 ± 3.7 ng/mL after treatment. Circulating concentrations of IGF-I increased significantly after treatment (52.2 ± 18.9 ng/mL) vs before treatment (26.6 ± 12.8 ng/mL). The 25-OH-D concentrations were correlated significantly with the IGF-I levels before and after treatment ( r = 0.603 and r = 0.59, respectively; P < .001). The GVSDS after treatment was correlated with the increase of IGF-I and 25-OH-D levels ( r = 0.325 and r= 0.314, respectively; P < .01). These data denote that the accelerated linear growth after treatment of nutritional vitamin D deficiency is mediated through activation of the growth hormone/IGF-I system and suggests an important role of vitamin D as a link between the proliferating cartilage cells of the growth plate and growth hormone/IGF-I secretion. Three different sequential stages of vitamin D deficiency can be recognized according to the clinical/radiological, biochemical, and hormonal data of patients at presentation.