Some vegetables, such as spinach, contain oxalates and some grains contain phytates. Both of these partially block the absorption of calcium. Caffeine and high protein intake can interfere with absorption also. The most well known function of calcium is to preserve bone density. More than 25 million Americans, mostly women, suffer from osteoporosis.
Osteoporosis is an ongoing condition of brittle bones becoming weaker.
This disease puts individuals at greater risk for hip and other bone fractures. Bones act as a reservoir for calcium. If there is not enough calcium circulating in the blood to meet the body's needs for the mineral, it will be pulled from the bones. Typically, people keep building up calcium in the bones through their late 20's and early 30's. After age 30 to 35 bones begin to naturally lose the minerals that give them strength, like calcium.