Vitamin D exists in the body in three forms. Cholecalciferol, or vitamin D-3, is made naturally when sunlight shines on bare skin. It can be taken as a supplement. According to the Vitamin D Council, calcidiol, or 25D3, is a prehormone made from cholecalciferol. The test for vitamin D levels, called 25-hydroxyvitaminD, measures this form. The body makes calcitriol, or 1,25D3, in the kidneys and other tissues from calcidiol. Calcitriol is the most potent steroid hormone in the body and considered the active form of vitamin D.
Bone Health
Vitamin D helps the body absorb and use calcium for strong bones. People form most of their bone mass while young and begin to lose it as they age. Vitamin D is important during bone formation in youth and throughout life. According to the University of Maryland Medical Center, postmenopausal women can take vitamin D and calcium supplements to help prevent osteoporosis. Taking supplements also helps prevent osteomalacia, a softening of bones in adults. Children deficient in vitamin D can develop rickets, which results in softening and distortion of bones.
Parathyroid Health
The four parathyroid glands in the neck produce a hormone which helps the body store and use calcium and phosphorus. According to the World's Healthiest Foods website, when blood calcium gets too low, the parathyroid glands excrete parathyroid hormone. It causes the release of calcium from the bones and triggers the kidneys to retain calcium. If the parathyroid glands aren't functioning properly, too much calcium can be removed from bones, and too much left in the blood. Vitamin D deficiency is a major risk factor for such malfunctioning of the parathyroid glands. According to the University of Maryland Medical Center, doctors often use vitamin D to treat parathyroid disorders.
Cardiovascular Health
The University of Maryland Medical Center explains that too much calcium in the blood contributes to plaque buildup in arteries, which can lead to heart attack or stroke. Low levels of vitamin D can cause too much parathyroid hormone to be released, which can lead to high blood calcium levels. Some studies also show that people with lower levels of D have a higher risk of developing hypertension and diabetes, both risk factors for cardiovascular disease.
Healthy Immune System
According to the World's Healthiest Foods website, researchers have found vitamin D receptors on macrophage cells which are part of the body's immune system. When the cells are triggered by vitamin D, they release substances called antibacterial peptides, which help prevent infection.
Weight Control
The University of Maryland Medical Center reports that people with low levels of vitamin D are more likely to be overweight than people with high levels. One study supplemented postmenopausal women with vitamin D and calcium and found they were less likely to gain weight than those who did not get the supplements. However, the difference in weight gain was small.
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