Whenever we think of our need for calcium, the majority of us think about bone strength and teeth most likely in that order. However, calcium plays a part in other functions in the body such as blood clotting, muscle contraction, brain function, etc. About 99% of calcium in the body is stored in the bones and teeth. When the blood level of calcium comes up short for other functions, calcium will be pulled from the bones. In other words, those other needs for calcium are so important that they are met one way or another. Our bodies cannot make calcium so the needs have to be met by diet and supplements. How you handle this should come from a discussion with your doctor. Keep in mind that we don't really absorb all of the calcium we get from either diet or supplements and that amount absorbed decreases with age. The percentage is probably less than we think. It is wise to space calcium supplements throughout the day to maximize absorption. The sources that I read recommend taking no more than 500mg at one time.
Resources: ACSM Action Plan For Osteoporosis Kerri Winters-Stone, PhD
The BEST Exercise Program for Osteoporosis Prevention (authors listed in previous post)
This book is part of the DSW Fitness Center For Continuing Education program