VITAMIN D


I. Sources and recommended intake

  1. Primary dietary sources are meat, fatty fish, eggs, and fortified milk (in US)
  2. Also synthesized in humans with exposure to ultraviolet-B radiation (e.g. sunlight)
  3. Recommended dietary intake:
    1. < 12mo: 400 IU/d
    2. 1-18yo: 600 IU/d
    3. Adults: 600IU/d (800IU if > 70yo)
    4. Some at-risk adults might require 1500IU

II. Physiology

  1. Specific compounds grouped under heading of "vitamin D":
    1. Ergocalciferol ("vitamin D2")-Found in some plants
    2. Cholecalciferol ("vitamin D3")-The compound synthesized in humans with UV exposure; SUpplements are derived from oily fish
  2. For pharmacologic vitamin D preparations, 10 mcg = 400 IU

III. Vitamin D deficiency

  1. Risk factors
    1. Low sunlight exposure
    2. Low dietary intake
    3. Infants exclusively breast-fed
    4. Dark skin pigmentation
    5. Elderly are at particular risk for deficiency because of low sunlight exposure, decreased synthetic capacity of Vit. D in the skin, and decreased absorption and activation of the vitamin.
  2. Diagnosis
    1. Serum assays can be variable; 25-hydroxyvitamin D is usually what is measured
    2. Deficiency often defined as 25-hydroxyvitamin D level <20 ng/mL (50 nmol/L)
    3. There may be adverse effects with elevated levels (> 50 ng/mL)
  3. Treatment
    1. Lowers risk of osteoporosis
    2. May lower risk of falls in elderly
    3. Treatment in children
      1. 2,000 IU/d of vitamin D2 or D3, or 50,000 IU Qwk x 6wks

IV. Supplementation

  1. Can supplement with either D2 or D3 (see above) but D3 supplementation raises serum levels more than D2
  2. Adequate levels of vitamin D are associated with reduced risk of falls in patients > 65yo and also in hip fractures
  3. Evidence for other benefits from vitamin D supplementation (reductions in BP, coronary events, infections, type 1 DM, multiple sclerosis, and malignancies) is very limited as of 2012
  4. Vitamin D + Ca for elderly at risk for deficiency (home-bound, poor nutritional status, unsunny climate)
    1. 389 healthy men & women >65yo, residing in non-institutional settings, randomized to Ca 500mg + vit. D3 700IU QD vs. placebo; at 3y f/u, tx group had sig. increases in bone density at femoral neck, spine, and total body; sig. decreased incidence of a first nonvertebral fx (6% vs. 13%) (NEJM 337:670, 1997-JW)
    2. In a trial of 2686 community-dwelling pts 65-85yo randomized to vit. D 100IU PO Q4mos vs. placebo, over 5y f/u, vit. D group had sig. lower incidence of fx (RR 0.78) (BMJ 326:469, 2003--JW)
    3. In a meta-analysis of 5 RCT's of vitamin D vs. placebo in elderly populations (mean age 60y), use of vitamin D was ass'd with OR of 0.78 for falls (sig.) (JAMA 291:1999, 2004--abst)
    4. In a meta-analysis of seven randomized trials of Calcium + Vitamin D in elderly patients (mean age 79y), vitamin D at dose of 400IU was not associated with reduced risk of fracture, but 700-800IU/day was (OR 0.75, NNT = 50) (JAMA 293:2257, 2005--AFP)
    5. In a randomized study in 625 residents in nursing homes and assisted-living facilities randomized to vitamin D 1000IU/d vs. placebo + Ca supplements (600mg elemental ca/day), over 2y f/u, vit. D. recipients had sig. lower incidence of falls (1.37 vs. 1.86/person/yr_ (J. Am. Geriat. Soc. 53:1881, 2005--JW)
    6. In a study in 5,292 pts > 70yo with h/o low-trauma fractures randomized to vitamin D 800IU/d, Ca 1000mg/d, both, or placebo, at 24-62mo f/u, there was no sig. diff. in incidence of fracture, death, or falls between the two groups (Lancet 365:1599, 2005--JW)
    7. In a study in 36,282 postmenopausal women randomized to CaCO3 1g/d + Vit. D 400IU/d vs. placebo, over 7y f/u, there was no sig. diff. in overall incidence of spine, hip, or total fractures, though among the subgroup of women not using supplemental Ca/Vit. D outside the treatment protocol, RR for hip fx was sig. lower in supplemented group (HR 0.7); ctive-tx group had sig. higher incidence of kidney stones (WHI Trial; NEJM 354:669, 2006--JW)
    8. In a study in 3,314 community-dwelling women > 70yo with one of (prior fx, body weight < 58kg, fair or poor self-reported health, cigarette use, or maternal h/o gracture) randomized to calcium 1000 mg/vit. D3 800IU/d vs. printed information only, over 2 mo, there was no sig. diff. in incidence of self-reported fx (BMJ 330:1003, 2005--JW)
    9. In a meta-analysis of 12 randomized trials of oral vitamin D supplementation in 42,279 pts > 65yo, over at least 1y f/u, doses of < 400 IU/day was associated with no sig. diff. in incidence of nonvertebral fx, but doses of > 400 IU/d was associated with sig. lower incidence  of nonvertebral fx (RR 0.80); Ca supplementation was not associated with sig. additional decrease in nonvertebral fx risk (Arch. Int. Med. 169:551, 2009-AFP)

(Sources include Core Content Review of Family Medicine, 2012)