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Objective: Calcium demand is increased during pregnancy. However, few randomized controlled trials examined the effects of calcium supplementation on bone mass during pregnancy. This study determined effects of calcium and milk supplementation on maternal bone mineral density (BMD) and bone turnover in pregnant Chinese women with habitual low calcium intake. Methods: In this randomized controlled trial, 36 Chinese pregnant women (24-31 years, 18 gestational weeks) were randomly assigned to the following three arms (12 each): I, usual diet; II, 'I' + 45 g milk powder (containing 350 mg calcium); or III, 'II' + 600 mg calcium/day from gestational age of 20 weeks to 6 weeks post-partum (PP). BMD was measured post-treatment using dual-energy X-ray absorptiometry. Dietary intakes, 24-h urinary calcium, bone resorption (urinary hydroxyproline) and formation (serum osteocalcin) biomarkers were examined at the gestational age of 20 and 34 weeks, and 6 weeks PP. Results: A dose-dependent relationship was observed between calcium intake and BMDs. The BMD values were significantly higher in subjects with calcium and milk supplementation than those in the controls at the whole body and spine ( p < 0.05) but not at the hip sites. We found significant decreases in changes of urinary hydroxyproline, and significant increases in serum osteocalcin during the intervention period in the calcium/milk intervention groups than those in the control group (all p < 0.05). Conclusion: Calcium/milk supplementation during pregnancy is associated with greater BMD at the spine and whole body and suppresses bone resorption in Chinese women with habitual low calcium intake. [ABSTRACT FROM AUTHOR]