Home  >  Health Resources  >  Health Encyclopedia

Vitamin D

Vitamin D

Other name(s):

calciferol (vitamin D-3), cholecalciferol, dihydrotachysterol (a synthetic vitamin D), ergocalciferol (vitamin D-2), ergosterol (provitamin D-2), 7-dehydrocholesterol (provitamin D-3), 22-dihydroergosterol (vitamin D-4 or provitamin D-4)

General description

Vitamin D is a fat-soluble vitamin. It’s needed for bone growth and development. Because it’s stored by the body, taking too much of it can cause toxicity problems.

Vitamin D deficiency may cause rickets. This is a disease affecting the skeletal system.

Ergosterol (provitamin D-2) and ergocalciferol (vitamin D-2) are found in plants; 7-dehydrocholesterol is found in animals. Vitamin D is called the sunshine vitamin. This is because in humans, the biologically active form, calciferol (vitamin D-3) is formed after exposure to sunlight.

Vitamin D, with the parathyroid hormone, regulates calcium balance in the body. It maintains normal serum calcium levels and bone density. Either formed through the exposure of sunshine on the skin or obtained through the diet, vitamin D increases the absorption of calcium and phosphorus from the intestine. It also aids in the reabsorption of phosphorus from the kidney. Vitamin D is needed for normal bone growth. It’s also needed for repairing bones after a fracture. As a result, vitamin D plays a role in the growth and development of the skeletal system. It’s especially needed during infancy, childhood, and the teen years.

Medically valid uses

Vitamin D helps treat the following conditions:

  • Low calcium levels

  • Low phosphate levels

  • Defective bone development

  • Rickets

  • Certain types of abnormal muscle contractions

  • Osteomalacia

  • Vitamin D deficiency

Very powerful man-made forms of vitamin D have been used to treat renal rickets. This is a condition caused either by severe kidney disease or by an inherited disorder of renal calcium/phosphorus absorption.

Unsubstantiated claims

Please note that this section reports on claims that have not yet been substantiated through studies.

Vitamin D is said to help control heart rate. It may also prevent muscle weakness and improve arthritis.  Studies are also looking at vitamin D's role in preventing and treating cancer, psoriasis, and diabetes.

Recommended intake

Vitamin D is measured in International Units (IU). One IU equals 0.025 micrograms of vitamin D. The RDA is the Recommended Dietary Allowance.

Group

RDA/IU

RDA/mcg

Infants (0–12 months)*

400 IU

10 mcg

Children (1–18 years)

600 IU

15 mcg

Adults (19–70 years)

600 IU

15 mcg

Adults (70 years and older)

800 IU

20 mcg

Pregnant women

600 IU

15 mcg

Breastfeeding women

600 IU

15 mcg

* Adequate Intake (AI)

Adults can meet the requirement for vitamin D without needing supplements. You can do this by exposing your face, hands, arms, or back, without sunscreen, to the sun for 10–15 minutes at least two times a week.

People over the age of 50 years may be at increased risk of vitamin D deficiency. As people age, skin cannot synthesize vitamin D as well. Plus, the kidney is less able to convert vitamin D to its active hormone form. For these reasons, older adults may need vitamin D supplements.

People with darker skin are less able to make vitamin D from sunlight. So, they must get enough vitamin D from foods or supplements.

Food source

Nutrient content per 100 grams

Cod liver oil

22,220 IU

Salmon (Atlantic)

650 IU

Salmon (Chinook)

500 IU

Tuna

249 IU

Shrimp

150 IU

Mushrooms

149 IU

Sunflower seeds

92.2 IU

Eggs

49.9 IU

Liver

49.9 IU

Milk, fortified

40 IU

Vitamin D is stable in heat. It doesn’t need to be refrigerated. It’s only slightly sensitive to light.

Freezing foods high in vitamin D content (salmon or mackerel) doesn’t reduce their vitamin D content. Vitamin D content stays high even when foods are cooked.

When a deficiency of vitamin D occurs during infancy or childhood, the skeletal system develops abnormally. This leads to rickets. It rarely occurs in tropical climates. But rickets was common among children in northern cities of the U.S. and among African American children until milk became fortified with vitamin D supplements. Since vitamin D is needed to keep normal bone strength, deficiencies of vitamin D in an adult can lead to loss of calcium and contribute to softening of bones (osteomalacia). It can also lead to thinning of the bones (osteoporosis).

More vitamin D is needed by those who live in subpolar and polar regions where long winter nights cause reduced sun exposure. Melanin, the pigment that gives skin its color, can reduce the skin’s ability to make vitamin D. People with darkly pigmented skin who are unable to get enough sun exposure or consume recommended amounts of vitamin D may need a vitamin D supplement.

Malabsorption syndromes, especially due to increased fat loss in the stool (steatorrhea), can cause an increased need for vitamin D. These issues include lactose intolerance, tropical and non-tropical sprue, celiac disease, cystic fibrosis, ulcerative colitis, Crohn's disease, and pancreatitis.

Liver diseases, such as cirrhosis or kidney failure, can cause vitamin D deficiencies. So can ingesting large amounts of snack foods containing the fat substitutes Olestra or Olean, or the chronic use of mineral oil.

Women who are pregnant or breastfeeding may need to take supplements, but you should talk to your healthcare provider first.

Vitamin D deficiency causes rickets in children. It causes osteomalacia or osteoporosis in adults. These problems result from failure to mineralize new bone. Eventually this leads to demineralization and weakening of existing bone. Deficiency in infants can lead to soft skill (craniotabes).

Symptoms of rickets include the following:

  • Delayed closure of the soft spot (anterior fontanel). It may take until after the second year of life

  • A larger than normal head (macrocephaly)

  • Defects in the enamel of forming teeth

  • Knobby growths at the points where the ribs join the sternum (rachitic rosary

  • Thickening of the ankles and wrists

  • Curvature of the spine (lordosis or scoliosis)

  • Bowing of the legs

  • Greenstick fractures

  • Muscle weakness

  • Delayed motor development

Some of the symptoms of osteomalacia include diffuse bone pain (often in the hips) and muscle weakness.

Some of the symptoms of osteoporosis include back pain, loss of height as the vertebrae become compressed, and fractures that occur with minimal trauma.

Side effects, toxicity, and interactions

Vitamin D in large dosages is toxic. Symptoms in children and adults often come on after several months of heavy use. They include the following:

  • Constipation

  • Decreased muscle tone (hypotonia)

  • Joint pain

  • Irritability

  • Being thirstier than normal

  • Making more urine than normal

  • Loss of appetite

  • Vomiting

  • High blood pressure (hypertension)

Too much vitamin D can also damage the valves in the heart and the kidneys. This is due to calcification.

You shouldn’t take vitamin D if you have hypercalcemia, signs of vitamin D toxicity, hypervitaminosis D, increased sensitivity to the effects of vitamin D, or decreased kidney capacity.

Use vitamin D with caution if you have arteriosclerosis, hyperphosphatemia, kidney problems, sarcoidosis, or heart problems.

Vitamin D can interact with certain medicines. Talk to your healthcare provider if you take any of the following medicines:

  • Antacids, especially those containing magnesium)

  • Digitalis glycosides. These include lanoxin, digoxin, and digitoxin.

  • Verapamil

  • Cholestyramine

  • Phenytoin

  • Thiazide diuretics

  • Barbiturates

  • Mineral oil

When taking vitamin D supplements, you shouldn’t use magnesium, phosphorus, or calcium unless your healthcare provider says to.

 

 

Today's Interactive Tools

 

Related Items