Vitamin D, playfully known as the "sunshine vitamin", plays a large and diverse role in the human body. Vitamin D works directly with calcium in order to produce and maintain strong bones, support immune system health, promote cellular function, and even help prevent cancer. Vitamin D is absorbed and produced when your skin is exposed to sunlight or when certain foods are consumed.
The two varieties of vitamin D are vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). People who live in darker, northern areas of the world and the elderly may be at an increased risk of deficiency. People who have darker skin tones are unable to absorb sunlight to the same extent as those with fair skin tones and may be at an increased risk of deficiency. Because of these risk factors, about 3/4 of the U.S adult population is estimated to have suboptimal vitamin D levels.
Through binding to the vitamin D receptor (VDR), 1,25-dihydroxyvitamin D can regulate the expression of hundreds of genes involved in skeletal and other biological functions. Vitamin D is essential for the maintenance of bone mineralization through the regulation of calcium and phosphorus homeostasis. Vitamin D also exhibits many non-skeletal effects, particularly on the immune, endocrine, and cardiovascular systems. Vitamin D is also important for normal bone development and maintenance.
Severe vitamin D deficiency causes rickets in children and osteomalacia in adults. Secondary hyperparathyroidism due to vitamin D insufficiency can increase bone breakdown and precipitate osteoporosis. Randomized clinical trials indicate that high doses of supplemental vitamin D can reduce the risk of falls and fractures in older individuals. Vitamin D can regulate cell differentiation and growth by binding to the vitamin D receptor found in most body cells. Observational studies have reported associations between low sun exposure, poor vitamin D status, and increased risk of developing colorectal and breast cancer. Randomized clinical trials are needed to evaluate whether cancer prevention may benefit from vitamin D supplementation.
Also known as: Alfacalcidol: 1-alpha-hydroxycholecalciferol, 1-alpha-hydroxycholécalciférol, 1 alpha (OH)D3. Calcifediol: 25-HCC, 25-hydroxycholecalciferol, 25-hydroxycholécalciferol, 25-hydroxyvitamin D3, 25-hydroxyvitamine D3, 25-OHCC, 25-OHD3, Calcifédiol. Calcipotriene: Calcipotriène, Calcipotriol. Calcitriol: 1, 25-DHCC, 1, 25-dihydroxycholecalciferol, 1, 25-dihydroxycholécalciférol, 1, 25-dihydroxyvitamin D3, 1, 25-dihydroxyvitamine D3, 1, 25-diOHC, 1, 25(0H)2D3. Cholecalciferol: 7-déhydrocholestérol Activé, Activated 7-dehydrocholesterol, Cholécalciférol, Colecalciferol, Colécalciférol, Vitamin D3. Dihydrotachysterol: DHT, Dihydrotachystérol, dihydrotachysterol 2, dichysterol, Vitamine D3. Ergocalciferol: Activated Ergosterol, Calciferol, Ergocalciférol, Ergocalciferolum, Ergostérol Activé, Irradiated Ergosterol, Ergostérol Irradié, Viosterol, Viostérol, Vitamin D2, Vitamine D2. Paricalcitol: 19-nor-1, 25-dihydroxyvitamin D2, 19-nor-1, 25-dihydroxyvitamine D2, Paracalcin. Fat-Soluble Vitamin, Vitamina D, Vitamine D, Vitamine Liposoluble, Vitamine Soluble dans les Graisses.
Diseases and Conditions
Vitamin D is effective for the following conditions:
- Familial hypophosphatemia
- Fanconi syndrome
- Renal osteodystrophy
- Vitamin D deficiency
Vitamin D is likely effective for the following conditions:
- Corticosteroid-induced osteopenia and osteoporosis
- Plaque psoriasis
- Dental cavities
- Heart failure
- Hyperparathyroidism-related bone loss in women
- Multiple sclerosis
- Respiratory tract infections
- Tooth retention
Vitamin D is likely safe when used appropriate orally and intramuscularly at a wide spectrum of dosages. The tolerable upper intake level of vitamin D for adults is 4,000 IU per day (if used orally long-term, dosage should not exceed this amount). However, in the case of vitamin D deficiency, doses of 50,000 IU/week may be taken in the short term for up to 12 weeks. It is likely unsafe to take oral doses of vitamin D exceeding 4,000 IU/day long-term since this can increase your risk for hypercalcemia.
Children, pregnant, and breastfeeding women may safely take vitamin D orally, appropriately, and under the supervision of a physician. Vitamin D is generally well-tolerated when taken orally in the appropriate doses, however intoxication may occur when taken in high doses. Symptoms of intoxication include hypercalcemia, azotemia, anemia, osteoporosis in adults, decreased growth in children, weight loss, calcific conjunctivitis, photophobia, metastatic calcification, pancreatitis, generalized vascular calcification, and seizures. Rare but possible adverse effects associated with vitamin D intake include hypertension and psychosis. There is also some concern that giving vitamin D to an infant within the first year of life may increase the risk for developing atopic conditions.
Vitamin D may interact with the following medications:
- Atorvastatin and other CYP3A4 substrates
- Cytochrome P450 3A4 (CYP 3A4) enzymes such as lovastatin (Mevacor), clarithromycin (Biaxin), cyclosporine (Neoral, Sandimmune), diltiazem (Cardizem), estrogens, indinavir (Crixivan), triazolam (Halcion)
- Low molecular weight heparins such as enoxaparin (Lovenox), dalteparin (Fragmin), and tinzaparin (Innohep)
- Thiazide diuretics such as chlorothiazide (Diuril), hydrochlorothiazide (HydroDIURIL, Esidrix), indapamide (Lozol), metolazone (Zaroxolyn), chlorthalidone (Hygroton), and verapamil
Supplement and Food Interactions
It is possible that vitamin D may interact with magnesium under specific conditions.
The Institute of Medicine publishes a recommended daily allowance (RDA) for vitamin D that is an estimate of the intake level necessary to meet the requirements of nearly all healthy individuals in the population. The RDA of vitamin D varies based on age as follows:
- 1-70 years of age - 600 IU daily
- 71 years and older - 800 IU daily
- Pregnant and lactating women - 600 IU daily
Most vitamin D supplements available without a prescription contain cholecalciferol (vitamin D3). Multivitamin supplements generally provide 400-1,000 IU (10-25 μg) of vitamin D2 or vitamin D3. Single ingredient vitamin D supplements may provide 400 to 50,000 IU of vitamin D3, but 400 IU is the most commonly available dose. A number of calcium supplements may also provide vitamin D. However, you may need significantly more or less vitamin D depending on your specific needs.
Foods which contain vitamin D include:
- Cod liver oil
- Tuna Fish
- Orange Juice (Fortified)
- Milk (Fortified)
- Yogurt (Fortified)
- Margarine (Fortified)
- Liver, Beef
- Certain Cereals
- Swiss Cheese
Vitamin D2 (ergocalciferol) is photosynthesized in plants, mushrooms, and yeasts. When vitamin D3 in skin is inadequate due to insufficient exposure to UVB radiation, oral intake of vitamin D is necessary to meet vitamin D requirements.