Postprandial metabolic responses to milk enriched with milk calcium are different from responses to milk enriched with calcium carbonate

The purpose of this study was to assess whether there are any differences in postprandial physiological responses to skim milk powder enriched with milk calcium (SMP + milk calcium) and skim milk powder enriched with calcium carbonate (SMP + CaCO3), with each of the milks providing 1200 mg calcium. This was a randomised, controlled, crossover study involving 16 men and 29 women over 55 years of age. Measurements of calcium and bone metabolism were taken after an overnight fast before each drink, and postprandially every hour for 8 h. The impact of time and drink on the responses was analysed by repeated measures of analysis of variance. Serum calcium was significantly higher between 2 and 8 h after consumption of SMP + CaCO3 compared with SMP + milk calcium (P < 0.0001). Serum phosphate was significantly higher between 2 and 5 h after drinking the SMP + milk calcium compared with SMP + CaCO3 (P < 0.0001). The level of parathyroid hormone (PTH) was virtually unchanged after consumption of SMP + milk calcium, but decreased between 1 and 4 h after SMP + CaCO3 (P = 0.02). The serum C-telopeptide level, a marker of bone resorption, was significantly lower after SMP + CaCO3, compared with SMP + milk calcium, between 4 and 8 h after drinking the milk (P < 0.05). We conclude that serum calcium levels have a higher increase after SMP + CaCO3 consumption than after SMP + milk calcium consumption, and that this is associated with lower serum PTH concentrations and a more prolonged postprandial decrease in bone resorption.