By A. Minocha MD, author: Guide to Alternative Medicine and Digestive System
Vitamin D or calciferol is actually a group of compounds with the molecule comprised of a cholesterol backbone. 1,25(OH)2-vitamin D is the physiologically active form of vitamin D. Several of the metabolites are biologically active.
Body vitamin D include is derived from production in skin as well as intestinal absorption.
Skin: Exposure of skin to sunlight leads to production of vitamin D in body.
Diet: In addition to vitamin D fortified milk, the dietary sources rich in vitamin D include fatty fish, cod-liver oil, and eggs. Vitamin D2 or ergocalciferol, a plant steroid is used for milk fortification. Other products that may be fortified include cereals, breads etc. Diet usually provides Vitamin D3.
Vitamin D homeostasis:
Functional significance of vitamin D:
Vitamin D and its metabolites are intricately related to calcium homeostasis and bone metabolism. With increasingly limited exposure to sun, Vitamin D insufficiency as measured by low levels of 25-OH vitamin D is a growing epidemic across the world especially among adolescents and the elderly.
Pathologic disease states with vitamin D involvement:
Although rickets in rare these days, subclinical vitamin D deficiency is common.
Since calcium metabolism is involved in not just in numerous metabolic functions in the body including bones, vitamin D deficiency may play a role not just in osteoporosis but also in impairment of immune function,increased risk of various malignancies including colon cancer as well as increased risk for heart disease.
Cancer: An increase of 25 nmol/L in 25-hydroxy-vitamin D levels is associated with a 17 percent decrease total cancer risk.
Bone fractures: Vitamin D and calcium supplementation reduces the risk of falls and fractures.
Vitamin D levels and mortality: Low levels of vitamin D are an increased risk of all cause mortality whereas supplementation of vitamin D results in reduced of all-cause mortality
Vitamin D levels: Best marker is the serum 25-OH vitamin D concentration. While there are considerable disagreements on the “normal” , a level below 20 to 30 ng/ml is considered abnormal. The "normals" may vary with the labs as well.
Vitamin D deficiency:
Vitamin D deficiency can be seen in 57 percent of hospitalized patients of whom 22 percent are severely deficient [Thomas 1998] Vitamin D stores decline with age, especially in the winter because of reduced sun exposure.
The deficiency or resistance may occur due to inadequate dietary intake, malabsorption, lack of sun exposure, liver or kidney dysfunction,or there may be end-organ resistence to vitamin D metabolites. Chronic use of corticosteroids results in decreased vitamin D dependent calcium absorption and hence bone disease.
Dose of vitamin D:
The tolerable upper intake level for vitamin D for healthy adults is 2000 IU per day. A minimum of 200 IU per day is needed in healthy adults. Many experts argue that the normal daily dose of vitamin D should be 1000-2000 IU per day. Some patients may even require higher doses and should be undertaken under close medical supervision.
Pregnant and lactating mothers: 400 IU/d
Infants who are exclusively breast fed: 400 IU/d. Since infant formulas are fortified with vitamin D, formula-fed infants require supplementation if they consume less than 1000 mL daily of formula.
Elderly: 800 IU/d plus atleast 1.2 g of elemental calcium per day.
Patients noncompliant with daily vitamin D therapy may benefit from high dose intermittent therapy (100,000 units every four months).
Prevention and treatment of osteoporosis 800 IU (20 micrograms) per day.
Toxic dose of vitamin D: Greater than 2000 IU per day.
Vitamin D is not innocuous and excess ingestion can lead to vitamin D intoxication. Subjects prone to this include not only those those who consume megadoses of supplements but also in patients on vitamin D replacement therapy for a variety of disorders. Manifestations of toxicity include hypercalcemia, hypercalciuria, altered mental status, polyuria, polydipsia, anorexia, vomiting, muscle weakness, and bone demineralization with pain.
Dr. Minocha's caveat:
I would like to pint out that some experts have questioned the issue of extent of prevelance of vitamin D deficiency for a variety of good reasons including in part to the paucity of reliable and reproducible blood tests and that the need for vitamin D may be different in different population sub-groups.
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