The major biologic function of vitamin D is to maintain normal blood levels of calcium and phosphorus. Vitamin D aids in the absorption of calcium, helping to form and maintain strong teeth and bones. It functions by increasing the uptake of calcium from the intestine through interaction with the parathyroid glands in controlling bone resorption and serum calcium levels. The skeleton is the body's reservoir of calcium and provides calcium through resorption of mineral when serum levels of this essential element drop. Vitamin D also increases reabsorption of phosphate by the kidney tubule, and may directly affect the osteoblast, the cell which forms bone.
Rickets
Without vitamin D, bones can become thin, brittle, soft, or misshapen. Rickets is a bone disease that affects children who are vitamin D deficient. It is defined as the failure of the osteoid to calcify. It causes progressive softening and weakening of the bones' structure. This softening results in bones becomimg flexable and gradually molded by forces such as bearing weigh exerted on them. Children with rickets may not grow to their full potential and may develope deformities of the body structure such as knonk-knees or bowed legs. It is very well documented that Vitamin D prevents rickets in children and osteomalacia in adults.
Osteomalacia
Osteomalacia is basically the same disease as rickets but occuring in adults. Rickets and osteomalacia were both recognized as being caused by vitamin D deficiency 75 years ago; their prevention and cure with fish liver oil constituted one of the early triumphs of nutritional science. The requirement for vitamin D has been pegged to these disorders ever since. Seniors in northern climates and people who do not receive direct sunlight for at least 45 minutes per week should take a vitamin D supplement.
Osteoporosis
Osteoporosis is a disease characterized by fragile bones, resulting in an increased risk of bone fractures. It is estimated that over 25 million adults in the United States have, or are at risk of developing osteoporosis. Osteoporosis is most common in post menopausal women.
Low levels of vitamin D and insufficient sunlight exposure (less than 20 minutes per day) are associated with both osteoporosis and a greater incidence of hip fractures. Additonally, older women are at greater risk because although normal bone is constantly being remodeled (broken down and rebuilt), during menopause, the balance between these two systems is upset, resulting in more bone being broken down (resorbed) than rebuilt.
Increased vitamin D intake is associated with less bone loss in older women. Vitamin D is needed to properly absorb calcium. Adequate amounts of vitamin D throughout one's life (in conjunction with exercise, proper nutrition, calcium, and magnesium) is necessary for preventing bone loss. Since bone loss increases the risk of fractures, vitamin D supplementation can help heal bone fractures from osteoporosis and decrease the risk of future bone breaks.
Having normal storage levels of vitamin D in your body helps keep your bones strong and helps prevent osteoporosis in elderly, non-ambulatory individuals, in post-menopausal women, and in individuals on chronic steroid therapy.
Osteoarthritis
Arthritis and its associated symptoms occur because of breakdown of cartilage in the joints. Just as vitamin D is needed for bone health, it is also needed to maintain healthy cartilage. Low intakes of vitamin D is linked to an increased risk of arthritis of the hip in older women and to joint changes seen on x-rays of both men and women. Progression of degenerative arthritis of the knee and hip is faster in people with lower vitamin D concentrations. Studies evaluating vitamin D use for osteoarthritis have found that it prevents the breakdown of cartilage.