Effect of Sodium Intake on Calcium Retention in Girls

Study Overview
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Brief Summary
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Optimal calcium retention is important for building bone mass within the genetic potential, a key to reducing risk of osteoporosis later in life. Calcium retention is high during the rapid growth period. The investigators know that urinary calcium is affected by sodium intake but the investigators do not know the effects of sodium intake during the growth spurt or the differences in calcium retention between blacks and whites. Our hypothesis was that a high dietary sodium increases the calcium intakes required for optimal calcium retention in both black and white adolescent girls. The investigators tested calcium retention while girls consumed a low and high sodium diet during three week periods. The subjects were housed in a Purdue fraternity house during the summer and they were supervised at all times by trained staff. During the summer of 1999, subjects consumed diets with 2 levels of dietary Na+ with a fixed diet low in calcium. On the next summer, they switched to a high calcium diet. Subjects collected fecal and urine daily for 20 days. Other measurements included daily body weight, blood pressure every other day, blood sample at the end of each session. Baseline measures included bone mass, self-assessment of pubertal development, a physical examination and diet history.

Detailed Description
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Optimal calcium retention is a prerequisite for building maximal peak bone mass within the genetic potential, a key to reducing risk of osteoporosis later in life. The investigators have determined that maximal calcium retention averages 423 mg/day during the period of rapid skeletal accretion in white girls at a mean dietary calcium intake of 1300 mg/d. Urinary calcium explains more than 50% of the variance in calcium retention. However, urinary sodium (i.e. sodium intake)is a major determinant of urinary calcium excretion and the effect of sodium intake on maximal calcium retention is not known. Nor is its effect known in black adolescents who have higher bone density and lower calcium excretion than white adolescents. The primary aim was to test the hypothesis that high dietary sodium increases the calcium intakes required for optimal calcium retention in both black and white adolescent girls. Calcium retention was measured at two levels of dietary sodium in a randomized crossover design on one of two levels of dietary calcium intake in black and white adolescent girls during three week metabolic periods. The investigators hypothesized that the mechanisms which regulate sodium reabsorption in the renal tubules also regulate calcium retention. Increased incidence of hypertension in blacks compared to whites has been attributed to increased sodium retention. Sodium intake induced changes in calcium and sodium retention in both races were related to changes in sodium handling (plasma renin activity, serum aldosterone, and salt sensitivity) and calcium regulating hormones, biomarkers of bone turnover and bone mass. The subjects were resident in a Purdue fraternity house, which was transformed during the summer into a metabolic unit. Subjects were supervised at all times by trained staff. The balance study was divided into 2 sessions of 3 weeks each during the summer of 1999 and 2000, with 2 levels of dietary Na+ during each summer. During the summer of 1999 subjects consumed a low calcium diet while in the summer of 2000 subjects consumed a high calcium diet. The Na+ intake periods were separated by a 2-week period, in which subjects were free to consume self-selected diets. Subjects collected fecal and urine daily for 20 days. Other measurements included daily body weight, blood pressure every other day, blood sample at the end of each session. Baseline measures included bone mass, self-assessment of pubertal development, a physical examination and diet history.

Official Title
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Effect of Sodium Intake on Calcium Retention in Black and White Adolescent Girls.

Conditions
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Osteoporosis

Intervention / Treatment
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* Other: Low Na diet (1.3 g/d)
* Other: High sodium diet (3.8 g/d)


Participation Criteria
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Eligibility Criteria
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Inclusion Criteria: White or black race (both parents and grandparents had to be white or black to be eligible in the study). Exclusion Criteria: < 11 or > 15 years body mass index (BMI) of < 15th or > 85th percentile for age history of amenorrhea, pregnancy or abortion, eating disorders, oral contraceptive or tobacco use.

Ages Eligible for Study
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Minimum Age: 11 Years
Maximum Age: 15 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: Prevention
Allocation: Randomized
Intervention Model: Crossover Assignment
Masking: Single


Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Experimental: High calcium diets (1300 mg or higher)<br> | Other: Low Na diet (1.3 g/d)<br>* 20 day controlled feeding study (live in) providing 1.3 grams per day of sodium.<br>* Other names: sodium calcium;Other: High sodium diet (3.8 g/d)<br>* 20 day controlled feeding study (live in) providing 3.8 grams per day of sodium.<br>* Other names: sodium calcium;|
| Experimental: Low calcium diet (800 mg/d)<br> | Other: Low Na diet (1.3 g/d)<br>* 20 day controlled feeding study (live in) providing 1.3 grams per day of sodium.<br>* Other names: sodium calcium;Other: High sodium diet (3.8 g/d)<br>* 20 day controlled feeding study (live in) providing 3.8 grams per day of sodium.<br>* Other names: sodium calcium;|

What is the study measuring?
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Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Change in calcium retention(mg/d)due to high (4g/d) and low (1g/d) sodium intake. |  | Up to 12 weeks | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Potassium retention in the black and white adolescent subjects |  | Up to 12 weeks | 
| Racial differences on the effects of high and low sodium intake levels on calcium intake requirements and calcium retention in adolescent girls |  | Up to 12 weeks | 
| Magnesium retention in the black and white adolescent subjects |  | Up to 12 weeks | 

 Terms related to the study
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Keywords Provided by Centre Hospitalier Valida
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calcium retention, sodium retention