The Effect of Vitamin D Supplementation During Caloric Restriction on Intestinal Calcium Absorption

Study Overview
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Brief Summary
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The purpose of this study is to learn how the amount of vitamin D supplementation influences intestinal fractional calcium absorption (a measure of the amount of calcium absorbed).

Detailed Description
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The extent of change in the amount of calcium that is absorbed with an increase in vitamin D supplementation is not known. This information is important for determining appropriate vitamin D requirements for optimal calcium absorption. During caloric restriction in postmenopausal women, we found that serum parathyroid hormone (PTH) explains 22% of the variance for the reduced calcium absorption (equivalent to 400 IU of Vitamin D per day). It is possible that higher dietary Vitamin D will increase serum 25-hydroxy-Vitamin D (25(OH)D) levels, offset serum PTH and thereby prevent a reduction in calcium absorption. This study seeks to determine if a high Vitamin D intake (a supplement of 2500 IU per day) can increase true fractional calcium absorption (TFCA) in postmenopausal women on a standard high-carbohydrate weight loss diet compared to weight maintenance, with the hypothesis that a high Vitamin D intake will raise serum 25(OH)D and offset the decline in TFCA during caloric restriction (vs. an increase in weight-stable women), and serum PTH will no longer be a major factor explaining changes in TFCA. Participants will be recruited for both weight loss and weight maintenance, and all will be randomly assigned to take either 2500 IU per day vitamin D supplement or matching placebo. All weight loss participants will attend 5-6 weekly counseling sessions (about 50 minutes per session). All participants will be asked to take a daily vitamin/mineral supplement and, depending on their usual food intake, they may be asked to take a calcium tablet to meet the recommended intake throughout the study period. To measure calcium absorption before and after the 6 weeks of weight loss, participants will go to the study site after an overnight fast where an IV will be placed and the participant will receive an infusion of a stable calcium isotope and consume a 4 oz beverage that also contains a stable isotope of calcium. Blood will be drawn, and then the participant will be asked to collect all urine for the next 24 hours. Body composition (fat, muscle mass, and bone mineral density) will be measured by a dual-energy x-ray absorptiometry (DXA) machine and peripheral quantitative computer tomography (pQCT). Participants will only be recruited in the winter and spring of each year.

Official Title
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Nutritional Regulation of Bone - Aim 3

Conditions
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Weight Loss, Vitamin D or Placebo

Intervention / Treatment
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* Behavioral: Weight Loss
* Dietary Supplement: Vitamin D 2500 IU
* Behavioral: Weight Maintenance


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: Postmenopausal women who are more than 2 years since last menses Obese or overweight Must live in the geographic vicinity of Rutgers University Exclusion Criteria: Currently on any medication known to influence calcium or bone metabolism, including HRT, or with evidence of diseases known to influence calcium metabolism (i.e. metabolic bone disease, hyperparathyroidism, untreated thyroid disease, significant immune, hepatic, or renal disease, significant cardiac disease [i.e., heart attack or stroke in the past 6 months., abnormal EKG], active malignancy or cancer therapy within the past year) History of kidney stones Weight gain or weight loss (5% of body wt) within 3 months prior to recruitment Participation in other investigational studies during the study period Travel for longer than 2 consecutive weeks during the study period Usually have a very high or low intake of calcium (more than 1500 or less than 500 mg per day)

Ages Eligible for Study
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Minimum Age: 50 Years
Maximum Age: 72 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: Treatment
Allocation: Randomized
Intervention Model: Parallel Assignment
Masking: Quadruple


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Placebo Comparator: WL<br> | Behavioral: Weight Loss<br>* Diet for weight loss for 6 weeks; all weight loss participants will attend 6 weekly counseling sessions (about 50 minutes per session)<br>|
| Experimental: WL + D<br> | Behavioral: Weight Loss<br>* Diet for weight loss for 6 weeks; all weight loss participants will attend 6 weekly counseling sessions (about 50 minutes per session)<br>Dietary Supplement: Vitamin D 2500 IU<br>* Daily Vitamin D 2500 IU supplement for 6 weeks<br>|
| Placebo Comparator: WM<br> | Behavioral: Weight Maintenance<br>* Diet for weight maintenance for 6 weeks<br>|
| Active Comparator: WM + D<br> | Dietary Supplement: Vitamin D 2500 IU<br>* Daily Vitamin D 2500 IU supplement for 6 weeks<br>Behavioral: Weight Maintenance<br>* Diet for weight maintenance for 6 weeks<br>|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Changes in Calcium absorption |  | 6 weeks | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Changes in serum and urine bone markers, hormones, glucose, proteins and genes |  | 6 weeks | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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bone mass, calcium absorption, bone quality, fracture risk