Vitamin D is one of the oldest
hormones that have been made in the earliest life forms for over 750 million years. Phytoplankton, zooplankton, and most plants and animals that are exposed to sunlight have the capacity to make
vitamin D.
Vitamin D is critically important for the development, growth, and maintenance of a healthy skeleton from birth until death. The major function of
vitamin D is to maintain
calcium homeostasis. It accomplishes this by increasing the efficiency of the intestine to absorb
dietary calcium. When there is inadequate
calcium in the diet to satisfy the body's
calcium requirement,
vitamin D communicates to the osteoblasts that signal osteoclast precursors to mature and dissolve the
calcium stored in the bone.
Vitamin D is metabolized in the liver and then in the kidney to
1,25-dihydroxyvitamin D [
1,25(OH)(2)D].
1,25(OH)(2)D receptors (VDR) are present not only in the intestine and bone, but in a wide variety of other tissues, including the brain, heart, stomach, pancreas, activated T and B lymphocytes, skin, gonads, etc.
1,25(OH)(2)D is one of the most potent substances to inhibit proliferation of both normal and hyperproliferative cells and induce them to mature. It is also recognized that a wide variety of tissues, including colon, prostate, breast, and skin have the enzymatic machinery to produce
1,25(OH)(2)D.
1,25(OH)(2)D and its analogs have been developed for treating the hyperproliferative disease
psoriasis.
Vitamin D deficiency is a major unrecognized health problem. Not only does it cause
rickets in children,
osteomalacia and
osteoporosis in adults, but may have long lasting effects. Chronic
vitamin D deficiency may have serious adverse consequences, including increased risk of
hypertension,
multiple sclerosis,
cancers of the colon, prostate, breast, and ovary, and
type 1 diabetes. There needs to be a better appreciation of the importance of
vitamin D for overall health and well being.