Calcium metabolism of Asian adolescents

Lu Wu, Purdue University

Abstract

The adolescent period is crucial for bone health because bone accumulates rapidly and up to half of the peak bone mass is accumulated during puberty. The calcium requirements of American adolescents were set at 1300 mg/d but the calcium requirement for Asian American adolescents has not been established. Using metabolic balance protocols, we determined calcium absorption efficiency, hormone response relevant to calcium homeostasis, and calcium retention of 31 Asian adolescents aged 11 to 15 y. Using stable calcium kinetic analyses, we evaluated the relative contribution of intestine, kidney and bone to calcium retention of Asian adolescents. Subjects were randomly assigned to 1 of 4 paired calcium intake groups between 600 to 1600 mg/d using a randomized order cross over design. Calcium metabolism and physiological predictors of calcium utilization were assessed and compared to white adolescents studied previously. Asian adolescents had lower habitual calcium intakes, lower vitamin D status and higher serum fasting PTH levels than white adolescents. There was a significant inverse association between relative calcium absorption and calcium intakes for Asian girls, but not boys. Compared to the white girls studied in previous camps using the same protocol, Asian girls had significantly higher calcium absorption efficiency and calcium retention across a wide calcium intake range. Our balance data also showed that Asian boys retained significantly higher calcium than Asian girls on the same calcium intake through lower fecal excretion. Sex steroid hormones also had a significantly extra effect on calcium retention for Asian subjects. The kinetic data showed that as calcium intake increased, calcium absorption efficiency, bone formation rate, bone resorption rate, and calcium excretion did not change significantly, while total absorbed calcium, the ratio of bone formation to bone resorption, fecal calcium excretion and calcium retained in bone increased for Asian girls. Asian girls had significantly higher calcium absorption efficiency from breakfast, a significantly higher ratio of bone formation to bone resorption, and significantly lower bone resorption rate than white girls. In this study, we also confirmed that there was a calcium dose effect on PTH suppression of adolescents. Because Asian adolescents had higher calcium absorption efficiency and higher calcium utilization than white adolescents across a wide range of calcium intakes, it is logical that with adequate calcium intake, Asians may achieve similar bone mass as whites. Calcium requirement for Asian adolescents needs to be further evaluated by nonlinear modeling of our data.

Degree

Ph.D.

Advisors

Weaver, Purdue University.

Subject Area

Nutrition

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