Calcium is an essential mineral found primarily in the body's bones and teeth, but it is also useful in maintaining muscle function and supporting the heart. According to the University of Maryland Medical Center, adults 19 to 50 years need a minimum of 1,000mg of calcium daily, while those older than 50 need 1,200mg daily. Although you may eat plenty of foods that contain calcium, your body needs other nutrients, including vitamin B12, to help you absorb this mineral to obtain its full benefits.
Vitamin B12 is also called cobalamin, and since it is a water-soluble vitamin, the body does not store it. As you digest food that contains vitamin B12, pancreatic enzymes free it to bind to a protein known as intrinsic factor. The body does not absorb vitamin B12 unless it is bound to intrinsic factor. Receptors that are in the small intestine are responsible for taking up vitamin B12 and intrinsic factor complex but can only do so when calcium is present.
When your blood levels of calcium run low, the body secretes parathyroid hormone, which in turn stimulates the body to absorb more calcium through digestion or to take calcium from bone to replenish the bloodstream. If your calcium levels are continuously low, you may be at risk of osteoporosis, as bone density decreases to maintain stable calcium levels in the bloodstream. Inadequate amounts of vitamin B12 may also reduce calcium absorption when the body attempts to stabilize blood calcium levels by taking it out of the bones.
In a 2005 study in the Journal of Bone and Mineral Research, lead author Katherine Tucker found that participants with low plasma levels of vitamin B12 had a significantly lower level of bone density than those with higher levels of vitamin B12. The study expanded on the association of increased fractures among people with pernicious anemia and states that there is a correlation between vitamin B12 and the work of osteoblasts, the cells responsible for building bone.
Calcium and vitamin B12 depend on each other for bone mineral density and overall absorption. If you have low levels of calcium, your body may not be able to absorb vitamin B12. Alternatively, low levels of vitamin B12 affect your bones and put you at an increased risk of fractures. Low levels of calcium may be related to problems with absorption or a lack of other nutrients such as vitamin D. Because your bones hold 99 percent of the calcium in your body, your bone density suffers if you are unable to absorb calcium.
Difficulty absorbing vitamin B12 can be caused by intestinal problems, such as with some gastrointestinal disorders or stomach surgery. Some people do not produce intrinsic factor, the protein necessary for vitamin B12 absorption, resulting in pernicious anemia. People with pernicious anemia may need vitamin B12 supplements daily to avoid illness and reduce the incidence of fractures associated with low bone density.