Calcium Citrate is best for absorption, and especially when it's combined with magnesium and vit. d3. I was on this combination for about 3 yrs. but stopped a few months ago due to concern over studies showing a connection between calcium supplements and heart disease. I asked my doc about this and he said that even though he was aware of the studies, in his opinion the results were not clear as of now, so he told me to stop the Calcium Citrate for 6 months (seeing as my vit. d was in good range), and to evaluate afterwards whether to resume taking it.