Vitamin D

Chief functions

  • Regulates absorption and use of calcium and phosphorus for development of bones and teeth
  • Aids in maintenance of healthy nervous and muscular systems by regulating blood calcium levels
  • Aids in calcium absorption from intestines and deposition of calcium in bones/teeth
  • Prevents excessive urinary loss of calcium and phosphorus
  • Stimulates maturation of cells and proper formation of skeleton
  • Helps with maintenance of bones in ears for hearing
  • Essential for mineral homeostasis

Possible benefits (ongoing research)

  • Insulin�may aid in function of insulin, therefore possibly aiding in regulation of blood glucose
  • Cancer�might aid in prevention or treatment of cancer by altering growth of cells
  • Immunity�might assist immune function, thereby helping defend against infection

Deficiency symptoms

  • Osteomalacia (adults)
  • Rickets (children)
  • Inadequate mineralization of the bone, leading to malformed bones
  • Deafness

Toxicity symptoms

  • Irreversible renal or heart damage
  • Causes calcium deposits in soft tissues�heart and lungs
  • Fragile bones
  • Hypertension
  • Kidney stones, stones in arteries, and excessive thirst
  • Mental and physical retardation
  • Constipation
  • Weight loss
  • Headaches
  • Loss of appetite
  • Irritability
  • Weakness
  • Nausea
  • Diarrhea
  • Dermatitis
  • Drowsiness

Stability

  • Stable to heat and oxidation
  • Destroyed by excess ultraviolet irradiation

Nutrient-nutrient reactions and absorption

  • Vitamin A is synthesized in the skin and also absorbed in the small intestine from foods containing vitamin D
  • For adequate absorption of vitamin D in the diet, at least 10% of calories must come from fat, because vitamin D is a fat-soluble vitamin
  • Conversion of active vitamin D takes place in the liver
  • Vitamin D is stored in the liver, skin, brain, bones, and other tissues
  • Cadmium can block the production of vitamin D in the skin
  • Sunblock with a SPF of 8 or higher prevents vitamin D synthesis
  • Clouds, smoke, smog, heavy clothing, window glass, and screens decrease vitamin D synthesis
  • Pantothenic acid (B5) is necessary for the synthesis of vitamin D in the skin

Dietary Reference Intakes

(updated in 2010)

 

Age

mcg

IU

0�1 year

10

400

1�50 years

15

600

51�70 years

15

600

71+ years

20

800

Pregnancy

15

600

Lactating

15

600

IU=international unit, mcg=microgram

40 IU=1 mcg

Tolerable Upper Limits

Age

Male

Female

Pregnancy

Lactation

0�6 months

1000 IU

25 mcg

1000 IU

25 mcg

7�12 months

1500 IU

38 mcg

1500 IU

39 mcg

1�3 years

2500 IU

63    cg

2500 IU

63 mcg

4�8 years

3000 IU

75 mcg

3000 IU

75 mcg

�9 years

4000 IU

100 mcg

4000 IU

100 mcg

4000 IU

100 mcg

4000 IU

100 mcg

Dietary sources

  • Fortified milk
  • Cheese
  • Cream
  • Butter
  • Margarine
  • Oysters
  • Salmon
  • Tuna
  • Fortified cereal
  • Liver
  • Cod-liver oil
  • Eggs

Groups at highest risk for deficiency

  • Dark-skinned children
  • Infants who are breastfed for a prolonged time with no supplementation
  • Children with inadequate intake of fortified vitamin D milk
  • Children on anticonvulsant therapy for epilepsy
  • Persons with intestinal malabsorption
  • Females who have had multiple pregnancies and have breastfed with little exposure to the sun
  • Women with a low-calcium intake

Other facts

  • Vitamin D exists in two forms, D2 (ergocalciferol) and D3 (cholecalciferol)
  • D2 is the supplemental form of vitamin D
  • D3 is the naturally occurring form of vitamin D, found in foods and manufactured in the skin with exposure to sunlight
  • Light-skinned people require 10�15 minutes/day of sun exposure for complete vitamin synthesis
  • Dark-skinned people require 3 hours/day of sun exposure for complete vitamin synthesis
  • Persons with limited exposure to sunlight may require a vitamin D supplement
  • Toxicity cannot occur from too much exposure to the sun
  • If an infant is breastfed and not exposed to sunlight, a daily supplement of 400 IU/day is recommended
  • Fortified foods are the major dietary source of vitamin D

 References and recommended readings

Mahan LK, Escott-Stump S, Raymond JL. Krause’s Food and the Nutrition Care Process. 13th ed. St Louis, MO: Elsevier Saunders; 2012.

 National Institutes of Health, Office of Dietary Supplements. Dietary supplement fact sheet: vitamin D. Available at: http://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional. Accessed August 24, 2012.

 US Dept of Agriculture, National Agricultural Library. DRI tables. Available at: http://fnic.nal.usda.gov/nal_display/index.php?info_center=4&tax_level=3&tax_subject=256&topic_id=1342&level3_id=5140. Accessed August 24, 2012.