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.