Vitamins
Vitamin D
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Vitamin D
, Vitamin D Replacement, Cholecalciferol, Ergocalciferol, Dihydrotachysterol
See also
Vitamin D Deficiency
Bone
Physiology
Gene
ral
See
Serum Calcium
for
Calcium Metabolism
Vitamin D2 (Ergocalciferol) and D3 (Cholecalciferol) are fat soluble
Although termed a
Vitamin
, it is actually a steroid
Hormone
Vitamin D acts at both cellular receptors as well as nuclear receptors (directly affecting
DNA Transcription
)
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
See
Serum Calcium
for
Calcium Metabolism
Images
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 Stone
s
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
Vitamin D Deficiency
Osteoporosis Prevention
Contraindications
Vitamin D Supplementation
Granuloma
tous 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 C
ontains 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
Breast
fed 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
Vitamin
s A, C and D with
Iron
Sunlight
Vitamin
s 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
Ooms (1995) J Clin Endocrinol Metab 80:1052-8 [PubMed]
Vitamin D does not reduce
Fracture
risk in adults over age 50 years (even in
Vitamin D Deficiency
)
LeBoff (2022) N Engl J Med 387(4): 299-309 [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]
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