Hi Keats,   Thank you for your question. Calcium carbonate and calcium citrate are the most easily absorbed for of calcium available, so you should probably stick with that. The main difference is that calcium citrate should be taken on an empty stomach for best absorption, and calcium carbonate should be taken with food. The calcium carbonate needs acid for absorption, and taking it with food increases the amount of acid in the stomach, leading to better absorption.   Also, you need to also be sure that you're getting enough Vitamin D. The body needs a certain amount of Vitamin D in order to be able to absorb calcium, so you might want to discuss with your doctor whether it's appropriate for you to take a Vitamin D supplement, which is available over the counter. The recommended daily dose would be one tablet or capsule (equivalent to 400 IU- international units) daily. Also, your body can only absorb so much calcium at one time, so the 1000 mg of calcium that you're taking should be taken in two separate doses. There are over-the-counter products available (such as Ost-cal + D, as well as generic versions) that contain both calcium and vitamin D, so that you only have to take one tablet at a time. If you chose to go with the Ost-cal + D, though, there are 600 mg of calcium in each tablet, so you'd need to take two tablets daily, and separate the dose so that you get the most out of it. I hope this helps!   Best of luck, Casey