The acute effects of calcium on calcium and bone metabolism
There has always been much controversy on the type, dosage and timing of calcium supplementation. I am not a firm believer in calcium carbonate due to the need for stomach acid for absorption (and almost all of us become deficient as we get older) and support the use of calcium citrate, malate or MCHC more strongly. This article finds that the timing of intake (morning or evening) does not affect the absorption (based on calcium’s effect on PTH secretion).
AJCN — Abstracts: Kärkkäinen et al. 74 (3): 335