Taking calcium supplements without K2 can improve bone strength, but it will also INCREASE THE RISK OF HEART DISEASE because only some of the calcium is deposited in the bones, where it is needed. Some of it is expelled via urine (which is why mainstream doctors recommend such high daily amounts of it) but the rest--dangerously--is packed around organs, where it does not belong and where it will do you harm. If deposited around the heart, it will increase your risk of heart disease; if deposited around the kidneys, it will increase the risk of kidney stones; if around the gallbladder, the risk of gallstones, etc. So you need to (1) take K2, which will deposit the calcium in your bones, where it belongs; (2) make sure you get enough D3 (from the sun whenever possible, then from supplements at other times), because it works synergistically and it will help your body absorb the calcium you ingest, whether from the diet or from a pill; and (3) reduce any calcium supplements you take, because once you have enough K2 and D3 your body will be able to use any calcium you ingest (instead of peeing it out and/or packing it around vital organs). You should also make sure you get enough magnesium if taking calcium, just don't take the two together because one blocks the absorption of the other. Happy bone health!