Until a few years ago, the only mention of vitamin D was when calcium metabolism was discussed. Vitamin D works with hormones secreted from the parathyroid glands, small glands just above the thyroid gland in the neck, to control calcium uptake and metabolism. But more recently, the research on vitamin D had burgeoned, along with the realization of how many people are deficient in this particular nutrient (88.1% of the world population is deficient in D). That's ironic in a way since vitamin D can be produced through the effects of ultraviolet rays exposure from the sun on the cholesterol found in the top layers of the skin. But for this to occur, the right conditions must exist. The sun must be in a certain part of the sky for the necessary level of UV to get to the earth and activate the endogenous vitamin D synthesis effect in the skin. If you have darker skin or have a higher level of body fat, this natural system of D production just won't work sufficiently. The older you are, the less efficient your body becomes at converting skin cholesterol into vitamin D. recent research on vitamin D shows that it affects numerous body systems and can offer preventive effects against a wide range of diseases. These include cardiovascular disease, cancer, diabetes, and multiple sclerosis. Other research shows that D is required for the full expression of the immune response. Without sufficient vitamin D available, a type of immune cell called Killer T-cells, which destroy incipient tumor cells in the body, cannot be activated. This partially explains why population areas that show lower than normal D levels also show a higher incidence of various types of cancer.
While in the past, the only clear-cut manifestation of a vitamin D deficiency was a disease called rickets in children, or osteomalacia in adults, both of which involve a failure to properly absorb calcium into bone, which compromises bone strength, it's now known that vitamin D receptors exist on nearly every organ in the body. Vitamin D is thought to activate over 1,000 genes in the body. As such, the health and preventive effects of vitamin D are much more far-ranging than previously thought.
What is often overlooked about vitamin D is that it's actually a prohormone. Ingested vitamin D goes through a conversion process, first in the liver, then continued in the kidneys, that results in a hormonal form of vitamin D known as 25-hydroxy D. This is the form of D that is active in the body through interacting with vitamin D-receptors throughout the body, including muscles.
You would think that athletes, who are usually thought to pay close attention to nutrition as a means of increasing athletic performance, would not be deficient in vitamin D, but that would be an incorrect assumption. I recently . . .