Effect of Sodium Intake on Calcium Retention in Girls
Condition: Osteoporosis
MeSH terms: Osteoporosis
Study type: Interventional

Summary: 
      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: 
      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.
    

Intervention name(s): Low Na diet (1.3 g/d); High sodium diet (3.8 g/d)
Intervention type(s): Other; Other
Intervention description(s): 20 day controlled feeding study (live in) providing 1.3 grams per day of sodium.; 20 day controlled feeding study (live in) providing 3.8 grams per day of sodium.
Other intervention name(s): low sodium; sodium calcium; high sodium; sodium calcium
Intervention MeSH terms: Calcium, Dietary; Calcium
Allocation: Randomized
Intervention model: Crossover Assignment
Masking: Single (Participant)
Primary purpose: Prevention
Keywords: calcium retention; sodium retention