Vitamin D Deficiency in Adolescent Girls

Study Overview
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Brief Summary
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Fibroblast growth factor 23 (FGF23) is a newly discovered hormone which regulates phosphate and vitamin D levels. In this study, we are looking at what the normal levels of FGF23 are in adolescent girls and how these levels vary with other hormonal measurements. We will also be looking at whether vitamin D supplementation in adolescents who are deficient in vitamin D alters the levels of FGF23 and other factors including insulin resistance.

Detailed Description
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Fibroblast growth factor 23 (FGF23) is a newly discovered hormone. Its primary function is to regulate phosphate metabolism, which it does both by directly regulating phosphate excretion through the kidney as well as by regulating vitamin D activity. What controls FGF23 levels is still under investigation; potential factors include dietary phosphate intake and vitamin D levels. In this pilot study, we aim to investigate what the normal levels of FGF23 are in healthy girls and how these are related to other measurements of bone and mineral metabolism. Since vitamin D deficiency is very common in healthy girls, we expect a subset of the subjects in this study to be vitamin D deficient. We will then randomize these girls to vitamin D repletion or placebo and follow changes in FGF23 levels. Vitamin D deficiency has also been implicated in insulin resistance which is a precursor to diabetes. We will therefore also look at changes in insulin resistance with vitamin D repletion.

Official Title
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Vitamin D Deficiency in Adolescent Girls

Conditions
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Healthy, Vitamin D Deficiency

Intervention / Treatment
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* Dietary Supplement: ergocalciferol
* Other: placebo pill


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: healthy girls aged 9-18 years Exclusion Criteria: significant cardiac, hepatic, oncologic, or psychiatric disease a history of malabsorption, kidney stones, hypoparathyroidism, or growth hormone deficiency pregnancy diabetes mellitus BMI>/= 99th percentile for age and sex fracture within the preceding 3 months hypogonadism (no pubertal development by age 12, absence of menarche by age 14) serum calcium <8 mg/dl or >11 mg/dl radiographic evidence of rickets use of medications know to affect serum phosphate levels including phosphate-binding antacids, sodium etidronate, calcitonin, excessive doses of vitamin D (>1000 units per day), excessive doses of vitamin D (>20,000 units/day), calcitriol, growth hormone, or anti-convulsants. use of hormonal birth control

Ages Eligible for Study
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Minimum Age: 9 Years
Maximum Age: 18 Years

Sexes Eligible for Study
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Female

Accepts Healthy Volunteers
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Accepts Healthy Volunteers

Study Plan
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How is the study designed?
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Design Details

Primary Purpose: Basic Science
Allocation: Randomized
Intervention Model: Parallel Assignment
Masking: Quadruple


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Active Comparator: Ergocalciferol<br>Weekly ergocalciferol for 16 weeks | Dietary Supplement: ergocalciferol<br>* ergocalciferol (a dietary form of vitamin D). 50,000 units by mouth once a week for 16 weeks.<br>* Other names: vitamin D;|
| Placebo Comparator: Placebo<br>Placebo pill. Note that all subjects in this arm will receive vitamin D repletion at the conclusion of the study. | Other: placebo pill<br>* placebo pill once weekly for 16 weeks. At the end of the study, subjects in this arm will receive vitamin D repletion<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| change in FGF23 level with vitamin D repletion |  | baseline and 16 weeks | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| change in bone turnover markers with vitamin D repletion |  | baseline and 16 weeks | 
| change in mineral metabolism factors with vitamin D repletion |  | baseline and 16 weeks | 
| change in insulin sensitivity with vitamin D repletion |  | baseline and 16 weeks | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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FGF23, FGF-23, vitamin D, vitamin D deficiency, insulin resistance, Healthy volunteers