Effect of Sodium Intake on Calcium Retention in Girls

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

67 participants

Study Classification

INTERVENTIONAL

Study Start Date

1999-01-31

Study Completion Date

2000-08-31

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.

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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.

Conditions

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Osteoporosis

Study Design

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Allocation Method

RANDOMIZED

Intervention Model

CROSSOVER

Primary Study Purpose

PREVENTION

Blinding Strategy

SINGLE

Participants

Study Groups

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High calcium diets (1300 mg or higher)

Group Type EXPERIMENTAL

Low Na diet (1.3 g/d)

Intervention Type OTHER

20 day controlled feeding study (live in) providing 1.3 grams per day of sodium.

High sodium diet (3.8 g/d)

Intervention Type OTHER

20 day controlled feeding study (live in) providing 3.8 grams per day of sodium.

Low calcium diet (800 mg/d)

Group Type EXPERIMENTAL

Low Na diet (1.3 g/d)

Intervention Type OTHER

20 day controlled feeding study (live in) providing 1.3 grams per day of sodium.

High sodium diet (3.8 g/d)

Intervention Type OTHER

20 day controlled feeding study (live in) providing 3.8 grams per day of sodium.

Interventions

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Low Na diet (1.3 g/d)

20 day controlled feeding study (live in) providing 1.3 grams per day of sodium.

Intervention Type OTHER

High sodium diet (3.8 g/d)

20 day controlled feeding study (live in) providing 3.8 grams per day of sodium.

Intervention Type OTHER

Other Intervention Names

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low sodium sodium calcium high sodium sodium calcium

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.

Minimum Eligible Age

11 Years

Maximum Eligible Age

15 Years

Eligible Sex

FEMALE

Accepts Healthy Volunteers

Yes