Calcium retention in adolescent boys on a range of controlled calcium intakes.

Background: National calcium requirements in the United States for boys are based on data from girls. On average, boys develop larger skeletons than do girls, yet it is unknown whether the additional skeletal accretion in boys requires additional dietary calcium intake.

Objective: The objective was to determine calcium retention in adolescent boys in response to a range of controlled intakes and to compare the intake needed for maximal retention in boys with that needed in adolescent girls studied under the same conditions.

Design: Thirty-one boys aged 12-15 y participated in 3-wk metabolic balance studies testing a range (700-2100 mg/d) of calcium intakes in a crossover study design with a 2-wk washout period. Calcium intake was varied by using a beverage fortified with calcium citrate malate. After a 1-wk equilibration period, calcium retention was calculated as dietary calcium intake minus the calcium excreted in the feces and urine over the following 2 wk. The dietary intake at which maximal calcium retention occurred was determined by using a nonlinear regression model. The results in boys were compared with those obtained in 35 adolescent girls previously studied under the same protocol.

Results: Maximal calcium retention in boys was achieved at an intake of 1140 mg/d. Calcium retention was higher (by 171 +/- 38 mg/d) in boys than in girls at all calcium intakes studied.

Conclusion: The higher calcium retention in boys than in girls was attained through higher net calcium absorption and lower urinary excretion than in girls.