Effect of lactulose on calcium and magnesium absorption: A study using stable isotopes in adult men

Summary To evaluate the effect of lactulose on calcium (Ca) and magnesium (Mg) absorption, we performed a clinical trial with a double-blind, randomized, crossover design in 24 healthy adult male volunteers. The absorptions of Ca and Mg were evaluated by a single-labeling method using stable isotopes. The test foods, containing lactulose at a dose of 0 g (placebo), 2 g (low-dose), or 4 g (high-dose) together with 300 mg of Ca containing 20 mg of 44 Ca, and 150 mg of Mg containing 28 mg of 25 Mg, were administered orally. Urine samples were collected for 8 h after the ingestion of the test food. The ratios of stable isotopes in urine ( 44 Ca/ 40 Ca and 25 Mg/ 24 Mg) were measured by ICP-MS (inductively coupled plasma-mass spectrometry). The urinary stable-isotopes ratios ( 44 Ca/ 40 Ca and 25 Mg/ 24 Mg) increased with lactulose dosage. Significant differences were observed in the Ca ratio between placebo and high-dose lactulose ( p � 0.01), and in the Mg ratio between placebo and low-dose lactulose and between placebo and high-dose lactulose ( p � 0.01). Lactulose ingestion did not change the levels of bone-resorption markers (type I collagen cross-linked N -telopeptide and deoxypyridinoline) in urine. The test foods did not cause any side effects. This study demonstrates that lactulose enhances the absorptions of Ca and Mg in adult men.