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

Study Results

Results pending

The study team has not published outcome measurements, participant flow, or safety data for this trial yet. Check back later for updates.

Basic Information

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Recruitment Status

COMPLETED

Clinical Phase

NA

Total Enrollment

83 participants

Study Classification

INTERVENTIONAL

Study Start Date

2007-03-31

Study Completion Date

2011-03-31

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).

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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.

Conditions

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Weight Loss Vitamin D or Placebo

Study Design

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Allocation Method

RANDOMIZED

Intervention Model

PARALLEL

Primary Study Purpose

TREATMENT

Blinding Strategy

QUADRUPLE

Participants Caregivers Investigators Outcome Assessors

Study Groups

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WL

Group Type PLACEBO_COMPARATOR

Weight Loss

Intervention Type BEHAVIORAL

Diet for weight loss for 6 weeks; all weight loss participants will attend 6 weekly counseling sessions (about 50 minutes per session)

WL + D

Group Type EXPERIMENTAL

Weight Loss

Intervention Type BEHAVIORAL

Diet for weight loss for 6 weeks; all weight loss participants will attend 6 weekly counseling sessions (about 50 minutes per session)

Vitamin D 2500 IU

Intervention Type DIETARY_SUPPLEMENT

Daily Vitamin D 2500 IU supplement for 6 weeks

WM

Group Type PLACEBO_COMPARATOR

Weight Maintenance

Intervention Type BEHAVIORAL

Diet for weight maintenance for 6 weeks

WM + D

Group Type ACTIVE_COMPARATOR

Vitamin D 2500 IU

Intervention Type DIETARY_SUPPLEMENT

Daily Vitamin D 2500 IU supplement for 6 weeks

Weight Maintenance

Intervention Type BEHAVIORAL

Diet for weight maintenance for 6 weeks

Interventions

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Weight Loss

Diet for weight loss for 6 weeks; all weight loss participants will attend 6 weekly counseling sessions (about 50 minutes per session)

Intervention Type BEHAVIORAL

Vitamin D 2500 IU

Daily Vitamin D 2500 IU supplement for 6 weeks

Intervention Type DIETARY_SUPPLEMENT

Weight Maintenance

Diet for weight maintenance for 6 weeks

Intervention Type BEHAVIORAL

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)

Minimum Eligible Age

50 Years

Maximum Eligible Age

72 Years

Eligible Sex

FEMALE

Accepts Healthy Volunteers

Yes