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Vitamin D
Aka: Vitamin D, Vitamin D Replacement, Cholecalciferol, Ergocalciferol, Dihydrotachysterol
- See also
- Vitamin D Deficiency
- Bone
- Physiology: General
- See Serum Calcium for Calcium Metabolism
- Images

- Vitamin D2 (Ergocalciferol) and D3 (Cholecalciferol) are fat soluble
- Although termed a Vitamin, it is actually a steroid Hormone
- Sources
- Vitamin D is synthesized in skin after exposed to sun (ultraviolet light)
- Also may be ingested and absorbed from Small Intestine
- Vitamin D circulates in blood as Calcifediol (Calcidiol, 25-hydroxyvitamin D3)
- Active form is Calcitriol (1,25 Hydroxycholecalciferol)
- Promotes renal and gastrointestinal Calcium absorption, and calcification of bone
- In excess, Vitamin D triggers Calcium absorption from bone
- Physiology: Synthesis
- Step 1a: Start with 7-Dehydrocholesterol (Cholesterol precursor)
- Skin exposure to sunlight or other ultraviolet light (290-315 nm of UV-B radiation)
- This pathway represents 90% of Vitamin D synthesis in humans
- Sun Exposure resulting in light pink skin (1 minimal erythema dose) = 20,000 IU (500 mcg) Oral Vitamin D
- Step 1b: Start with Dietary Vitamin D2 or D3
- Proceed to step 2 (bypasses sunlight-mediated synthesis pathway)
- Typically represents only 10% of Vitamin D source (unless specifically supplemented)
- Step 2: Cholecalciferol (Vitamin D3)
- Metabolized in liver by Vitamin D3-25 hydroxylase to 25-HYdroxycholecalciferol
- Step 3: Calcidiol (25-hydroxycholecalciferol, or 25-hydroxyvitamin D3)
- Metabolized in Kidney by 25-OH-D3-1a hydroxylase to 1, 25 Hydroxycholecalciferol (Calcitriol)
- Triggered by Parathyroid Hormone
- Step 4: Calcitriol (1, 25 Hydroxycholecalciferol)
- Calcitriol is the active form of Vitamin D)
- Pathophysiology
- Vitamin D Excess
- Hypercalcemia
- Ureteral Stones
- Vitamin D Deficiency
- Risk Factors
- Homebound elderly
- Inhabitants of Northern States
- Vitamin D Deficiency related conditions
- Children: Rickets
- Adults: Osteomalacia, Osteoporosis
- Indications: Vitamin D Supplementation or Replacement
- Osteoporosis Prevention
- Vitamin D Deficiency
- Contraindications: Vitamin D Supplementation
- Granulomatous disease (e.g. Tuberculosis, Sarcoidosis)
- Metastatic bone disease
- Williams Syndrome
- Preparations: Dietary and Supplement Sources
- Fish (Vitamin D3, most in fatty fish)
- Salmon (450 IU per 3 oz)
- Sardines
- Fish oils
- Tuna (150 IU per 3 oz)
- Egg yolk (40 IU or 1 mcg)
- Butter
- Liver and other organ meats
- Vitamin D Fortified Milk (USA) contains 100 IU (2.5 mcg) per cup
- Fortified Orange Juice contains 80 to 120 IU (2 to 3 mcg) per cup
- Multi-Vitamin Contains 400 IU (10 mcg) Vitamin D per tablet
- Signs: Vitamin D Deficiency
- See Vitamin D Deficiency
- Osteomalacia
- Muscular hypotonia
- Signs: Vitamin D Toxicity (related to Hypercalcemia)
- Headache
- Metallic Taste
- Vascular calcinosis or nephrocalcinosis
- Pancreatitis
- Nausea or Vomiting
- Dosing (higher than current RDA)
- Children and Adolescents: 400 IU (10 mcg) per day
- Adults Age 18-50 years: 400-800 IU (10-20 mcg) per day
- Adults Age >50 years or Osteoporosis (higher levels are controversial)
- Southern regions: 800 IU (20 mcg) per day
- Northern climates: 1000-2000 IU (25-50 mcg) per day may be required
- Expect a 0.4 ng/ml increase for every 40 IU (1 mcg) daily of Vitamin D
- Expect 4 ng/ml increase from 400 IU (10 mcg) daily
- Expect 40 ng/ml increase from 4000 IU (100 mcg) daily
- Vitamin D is fat soluble and is best absorbed with fat in the meal
- Dosing: Supplementation in Infants and Children under age 2 years
- Indications
- See Vitamin D Deficiency for risk factors
- Breastfed Infants
- Children and adolescents consuming <1 Liter (34 oz) Vitamin D Fortified milk daily
- Supplements with daily dose of 1 drop (equivalent to 400 IU or 10 mcg) for age under 2 years
- Carlson Baby D Drops
- Supplements with daily dose of 1 ml (equivalent to 400 IU or 10 mcg) for age under 2 years
- Enfamil Poly-Vi-Sol Multivitamin Supplement drops
- Enfamil Poly-Vi-Sol Vitamins A, C and D with Iron
- Sunlight Vitamins Just D Infant Vitamin Drops
- Twinlab Infant Care Multivitamin Drops with DHA
- References
- Casey (2010) Am Fam Physician 81(6): 745-50 [PubMed]
- Dosing: Children with Vitamin D Deficiency (Rickets)
- Ergocalciferol (D2, Calciferol)
- Dose: 25-125 mcg (1-5000 IU) PO/IM for 6-12 weeks
- Cholecalciferol (D3, 40,000 IU/mg)
- Option 1: 125-250 mcg (5-10,000 IU) PO for 3 months
- Option 2: 15,000 mcg (600,000 IU) divided qid x1 day
- Dihydrotachysterol (DHT, 120,000 IU/mg)
- Option 1: 500 mcg (0.5 mg) for single dose or
- Option 2: 13-50 mcg PO per day until resolved
- References
- Khatib (2005) Consultant Pediatrician 4:33-9 [PubMed]
- Dosing: Adults with Vitamin D Deficiency
- Mild (Serum 25-hydroxyvitamin D 8-15 ng/ml)
- Calcium 1200 to 1500 mg orally daily
- Vitamin D
- Option 1: Vitamin D 50,000 IU PO weekly for 8 weeks (repeat another course if Vitamin D <30 ng/ml)
- Option 2: Vitamin D 1000 IU daily per every 10 ng/ml shortfall in addition to maintenance for 6 weeks
- Example: Vitamin D 10 ng/ml
- Take 2000 IU (50 mcg) replacement in addition to 1000 IU (25 mcg) maintenance daily
- Option 3: Vitamin D 20-25 IU/kg IV daily (parenteral for hospitalized patients)
- Maintenance after acute replacement: Vitamin D 800-1000 IU (20-25 mcg) PO daily
- Severe (Serum 25-hydroxyvitamin D <8 ng/ml)
- Vitamin D 50,000 IU (1250 mcg) orally daily for 1-3 weeks
- Then maintain as mild deficiency doses above
- Monitoring Vitamin D level at 6-8 weeks after starting therapy
- Goal 25-Hydroxyvitamin D >30-40 ng/ml
- Storage of Vitamin D does not start until 40 ng/ml
- Efficacy: Vitamin D in Osteoporosis Prevention
- Dutch Study of 348 women over age 70 years
- Given Vitamin D 400 IU (10 mcg) or Placebo
- Vitamin D Group had greater BMD at 2 years
- Greater femoral neck Bone Mineral Density
- Placebo group had decreased Bone Mineral Density
- No change in femoral trachanter or distal radius BMD
- References
- Ooms (1995) J Clin Endocrinol Metab 80:1052-8 [PubMed]
- Efficacy: Conditions for which Vitamin D has no proven benefit
- Cardiovascular disease primary prevention (no proven benefit)
- Manson (2019) N Engl J Med 380(1): 33-44 [PubMed]
- Cancer primary prevention (no proven benefit)
- Manson (2019) N Engl J Med 380(1): 33-44 [PubMed]
- References
- Holick (2007) N Engl J Med. 357(3):266-81 [PubMed]
- LeFevre (2018) Am Fam Physician 97(4): 254-60 [PubMed]
- Norman (2007) J Steroid Biochem Mol Biol 103(3):204-5 [PubMed]
- Schneider (2006) Curr Opin Endocrinol Diabetes 13(6): 483-90 [PubMed]