Calcium and vitamin D are closely connected because the two nutrients are mutually dependent when it comes to performing their functions in the body. For example, vitamin D regulates the absorption and the metabolism of calcium as well as phosphorous; in fact, it is absolutely necessary for proper absorption of calcium. Most people associate strong teeth and bones with the role of calcium in nutrition, but calcium that is not absorbed cannot do its job. Another connection between calcium and vitamin D lies in the fact that vitamin D helps to maintain normal levels of calcium in the bloodstream.
The effects of vitamin D on the body include remineralization, growth and the repair of bones. It is interesting that a vitamin plays such a role in the maintenance of healthy bones and teeth because such activity generally is associated with calcium and other minerals, not vitamins. Calcium and vitamin D are so closely connected that vitamin D has been added to some calcium supplements to increase absorption. Absorption of calcium, however, can be increased naturally by a person getting adequate but healthy exposure to the sun, which stimulates the body to make its own vitamin D.
The benefits of calcium cannot be fully thought of as being independent of vitamin D because of the natural connection between calcium and vitamin D. For example, calcium also is necessary for the development and maintenance of healthy teeth and bones, proper clotting of blood, absorption of vitamin B12, regulation of cell permeability and proper utilization of iron. These vital life functions are not associated with vitamin D as a single nutrient. All of this changes, however, when considering the special connection between calcium and vitamin D.
It would, therefore, be correct to say that vitamin D is indirectly responsible for all of the same things for which calcium is responsible, because without vitamin D, the body cannot absorb the calcium that is put into it. Unlike vitamin D, which is not widely available in food, there are many good food sources of calcium. Dairy products, citrus fruits, figs and dark green leafy vegetables such as collard greens, mustard greens and turnip greens are excellent sources of calcium. A combination of a healthy diet rich in calcium and other essential nutrients, plus some daily exposure to the sun, is the best formula for ensuring that calcium and vitamin D are available in the body in adequate amounts to be able to perform all of their functions.