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vitamin D

What can high-vitamin D foods do for you?

  • Help keep your bones and teeth strong and healthy
  • Regulate the growth and activity of your cells

What events can indicate a need for more foods rich in vitamin D?

  • Bone pain and/or soft bones
  • Frequent bone fractures
  • Bone deformities or growth retardation in children
  • Lack of exposure to sunlight

Concentrated food sources of vitamin D include shrimp, milk, cod, and eggs.

Description

What is vitamin D?

Early in the 20th century scientists discovered that rickets, a childhood disease characterized by improper bone development, could be prevented by a compound isolated from cod liver oil referred to as “fat-soluble factor D,” now known as vitamin D. The vitamin was also called "calciferol," since it was found to boost calcium deposits in bone. Because vitamin D is so important in skeletal growth and strong bones, many foods are fortified with this vitamin to ensure that children obtain adequate amounts.

There are two basic types of vitamin D. Ergosterol is the basic building block of vitamin D in plants. Cholesterol is the basic building block of vitamin D in humans. When ultraviolet light from the sun hits the leaf of a plant, ergosterol is converted into ergocalciferol, or vitamin D2.

In just the same way, when ultraviolet light hits the cells of our skin, cholesterol is converted into cholecalciferol, or vitamin D3. Both of these substances - ergocalciferol in plants and cholecalciferol in humans - are usually referred to as "provitamin D," and both can be converted by the liver, and then the kidneys, into fully active vitamin D (called calcitriol).

Most of the time, however, when plant-based vitamin D (vitamin D2) is added to foods or supplements, the company only uses the plant food (like soybean) to get the ergosterol building block, and then irradiates this substance in a chemistry lab to produce vitamin D2.

How it Functions

What is the function of vitamin D?

Maintaining proper calcium levels in the blood

Although typically categorized as a fat-soluble vitamin, vitamin D actually functions more like a hormone than a vitamin. Calcitriol, the most metabolically active form of vitamin D, works with parathyroid hormone (PTH) to maintain proper levels of calcium in the blood. Low levels of calcium in the blood stimulate the secretion of parathyroid hormone from the parathyroid gland. PTH, then, stimulates the conversion of inactive forms of vitamin D to calcitriol. Calcitriol acts to increase the intestinal absorption of calcium, increase the reabsorption of calcium by the kidneys, and stimulate the release of calcium from the bone, thereby increasing blood calcium levels.

As we age, vitamin D becomes an even more critical nutrient not only for bone health, but for healthy teeth. A study published in the July 2004 issue of the American Journal of Clinical Nutrition that evaluated 11,202 subjects 20 years of age or older found that, in both men and women over 50, lack of vitamin D significantly increased risk of periodontal disease, a common chronic inflammatory gum disease that is an important risk factor for tooth loss.

Men with the lowest blood levels of vitamin D had a 61% higher risk of periodontal disease. Women with the least vitamin D in their blood had an even higher, 74% increased risk of periodontal disease. In men and women younger than 50, no significant association between vitamin D levels and periodontal disease was found.

So, if you're over 50, particularly if you live in northern latitudes or slather on the sunscreen to protect your skin from age spots or skin cancer, be sure to make vitamin D-rich foods staples in your healthy way of eating.

The World's Healthiest Foods Nutrient Rating System identifies the following as the best food sources of vitamin D: shrimp, cow's milk, cod, eggs, snapper, halibut, and goat's milk. For recipes featuring these vitamin D-rich members of the World's Healthiest Foods, click Recipes.(June 30, 2004)

Cell growth regulation
Alternatively, when blood levels of calcium are high, calcitriol decreases the intestinal absorption of calcium and stimulates the bones to take up calcium, thereby decreasing blood calcium levels. Calcitriol also participates in the regulation of cell proliferation, differentiation, and growth, which suggests a role for this vitamin in the prevention and treatment of various cancers.

Deficiency Symptoms

What are deficiency symptoms for vitamin D?

Vitamin D deficiency results in decreased absorption of calcium and phosphorous. As a result, prolonged vitamin D deficiency has a negative impact on bone mineralization. In infants and children, such a deficiency manifests itself as rickets, a condition characterized by bone deformities and growth retardation. Adults with vitamin D deficiency may experience bone pain and/or osteomalacia (soft bone).

Although vitamin D deficiency is relatively rare, it is important for individuals with limited sun exposure to include good sources of vitamin D in their diets. Homebound individuals, people living in northern latitudes, individuals who wear clothing that completely covers the body, and individuals working in occupations that prevent exposure to sunlight are at risk for vitamin D deficiency.

In addition, breast milk may not contain a sufficient amount of vitamin D so exclusively breast-fed infants may require supplemental vitamin D.

Toxicity Symptoms

What are toxicity symptoms for vitamin D?

Excessive dietary intake of vitamin D can be toxic. Toxicity of vitamin D can come from either its plant-based (D2) or animal-based (D3) form. Symptoms of toxicity include loss of appetite, nausea, vomiting, high blood pressure, kidney malfunction, and failure to thrive.

In 1997, the National Academy of Sciences set Tolerable Upper Intake Levels (ULs) for vitamin D as follows: infants, 0-12 months, 25 micrograms per day; children and adults, 50 micrograms per day; pregnant and lactating women, 50 micrograms per day.

Individuals with hyperparathyroidism, overactivity of the parathyroid gland, are at increased risk for vitamin D toxicity, and should not take supplemental vitamin D without consulting a physician.

Impact of Cooking, Storage and Processing

How do cooking, storage, or processing affect vitamin D?

Vitamin D is a stable compound. Neither cooking nor long-term storage significantly reduce vitamin D levels in food.

Factors that Affect Function

What factors might contribute to a deficiency of vitamin D?

Since vitamin D is a fat-soluble vitamin, a diet that is extremely low in fat and/or the presence of certain medical conditions that cause a reduction in the ability to absorb dietary fat may cause vitamin D deficiency.

These medical conditions include pancreatic enzyme deficiency, Crohn’s disease, celiac sprue, cystic fibrosis, surgical removal of part or all of the stomach, gall bladder disease, and liver disease. Symptoms of fat malabsorption include diarrhea and greasy stools.

Under certain circumstances, the conversion of inactive forms of vitamin D to calcitriol is impaired. For example, diseases that affect the parathyroid gland, liver and/or kidney impair the synthesis of the active form of vitamin D. In addition, the production of vitamin D precursors in the skin decreases with age.

Drug-Nutrient Interactions

What medications affect vitamin D?

The following medications impact the absorption, utilization and/or activation of vitamin D:
  • Anticonvulsant medications, including Dilantin, are used to control seizure activity in people with epilepsy and brain cancer, and those who have suffered head trauma through injury or stroke. These medications decrease the activity of vitamin D.
  • Bile acid sequestrants (Cholestyramine, Colestipol) are a class of drugs used to lower cholesterol levels. These drugs may reduce the intestinal absorption of the fat-soluble vitamins A, D, E, and K.
  • Cimetidine (Tagamet and Tagamet HB) prevents the release of hydrochloric acid into the stomach and is used to treat the symptoms associated with stomach and duodenal ulcers and acid reflux. This drug may reduce vitamin D activation by the liver.
  • Hormone replacement therapy may increase blood levels of vitamin D.
  • The corticosteroids are a family of anti-inflammatory drugs, including hydrocortisone and prednisone, that are commonly used in the treatment of autoimmune and inflammatory diseases, such as asthma, rheumatoid arthritis, and ulcerative colitis. These drugs reduce the activation of vitamin D.
  • Heparin, an anticoagulant prescription medication used to prevent blood clots after surgery, may interfere with vitamin D activation.
Vitamin D impacts the following medications:
  • Vitamin D may interfere with the effectiveness of calcium channel-blockers, a class of drugs used to treat chest pain, irregular heart beat and high blood pressure.
  • Taking supplemental vitamin D and calcium along with thiazide diurectics can cause blood levels of calcium to increase above normal levels.

Nutrient Interactions

How do other nutrients interact with vitamin D?

Vitamin D plays a role in maintaining normal blood levels of calcium. As a result, vitamin D impacts the absorption and storage of calcium. Vitamin D also stimulates the absorption of phosphorous.

Vitamin D is believed to regulate the production of certain calcium-binding proteins that function in the bones and kidneys. Because these binding proteins are dependent on vitamin K, an interrelationship between vitamin D and vitamin K is likely.

It has also been theorized that iron deficiency results in decreased vitamin D absorption.

Health Conditions

What health conditions require special emphasis on vitamin D?

Vitamin D may play a role in the prevention and/or treatment of the following health conditions:

Form in Dietary Supplements

What forms of vitamin D are found in dietary supplements?

The two forms of vitamin D used in dietary supplements are ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3). Ergocalciferol is often considered to be a vegetarian source of vitamin D, since it is often plant-derived (from soybeans, for example). However, yeast is also commonly used as a source of D2, as is cod liver oil. In addition, when the plant building block for vitamin D2 (ergosterol)is used to produce vitamin D2, it is irradiated in a chemistry lab in order to produce ergocalciferol, the D2 form.

Cholecalciferol, the D3 form of the vitamin, can be obtained from animal or microbial sources. The most common source for vitamin D3 is ergot, a fungus that can be grown on rye or other cereal grains. Many practitioners prefer the D3 source of the vitamin, since it is the naturally-occurring form of the vitamin in humans. However, both forms of the vitamin can be effective in boosting vitamin D status, and both forms can produce toxicity if overconsumed.

Vitamin D is often measured in International Units (IU) or micrograms. One microgram of cholecalciferol is equal to 40 IU of vitamin D.

Food Sources

Introduction to Nutrient Rating System Chart

The following chart shows the foods which are either excellent, very good or good sources of this nutrient. Next to each food name you will find the following information: the serving size of the food; the number of calories in one serving; DV% (percent daily value) of the nutrient contained in one serving; the nutrient density rating; and the food's World's Healthiest Foods Rating. Not all of our Daily Value standards are obtained from the FDA. In most instances, we used FDA Daily Values when available because they are widely recognized and apply to both men and women. However, when unavailable, we've used other science-based research to establish nutritional standards. Underneath the chart is a table that summarizes how the ratings were devised. Read more about our Nutrient Rating System.

Foods Ranked as quality sources of:
vitamin D
Food Serving
Size
Cals Amount
(IU)
DV
(%)
Nutrient
Density
World's
Healthiest
Foods Rating
Shrimp, MixedSpecies, Steamed, Boiled 4 oz-wt 112.3 162.39 40.6 6.5 very good
Milk, Cow, 2% 1 cup 121.2 97.60 24.4 3.6 very good
Cod, Pacific, Fillet, Baked, Broiled 4 oz-wt 119.1 63.50 15.9 2.4 good
Egg, Hen, Whole, Boiled 1 each 68.2 22.88 5.7 1.5 good
World's Healthiest
Foods Rating
Rule
excellent DV>=75% OR Density>=7.6 AND DV>=10%
very good DV>=50% OR Density>=3.4 AND DV>=5%
good DV>=25% OR Density>=1.5 AND DV>=2.5%

Public Health Recommendations

What are current public health recommendations for vitamin D?

In 1997, the National Academy of Sciences established the following Adequate Intake (AI) levels for vitamin D:

  • Infants and children: 5 micrograms
  • Teenagers: 5 micrograms
  • Adults up to 50 years of age: 5 micrograms
  • Adults 51-70 years: 10 micrograms
  • Adults above 70 years: 15 micrograms
  • Pregnant and lactating women: 5 micrograms

References

  • Buckley LM, et al. Calcium and vitamin D3 supplementation prevents bone loss in the spine secondary to low-dose corticosteroids in patients with rheumatoid arthritis. Ann Intern Med 1996; 125:961-968.
  • Dawson-Hughes B, et al. Effect of vitamin D supplementation on wintertime and overall bone loss in healthy postmenopausal women. Annals of Internal Medicine 1991; 115(7):505-512.
  • Dietrich T, Joshipura KJ, Dawson-Hughes B, Bischoff-Ferrari HA. Association between serum concentrations of 25-hydroxyvitamin D3 and periodontal disease in the US population. Am J Clin Nutr. 2004 Jul;80(1):108-13.
  • Feskanich D, Willett WC and Colditz GA. Calcium, vitamin D, milk consumption, and hip fractures: a prospective study among postmenopausal women. Am J Clin Nutr 2003 Feb;77(2):504-11.
  • Garland CF, Garland FC, Gorham ED. Calcium and vitamin D: Their potential roles in colon and breast cancer prevention. Ann N Y Acad Sci 1999;889:107-19.
  • Groff JL, Gropper SS, Hunt SM. Advanced Nutrition and Human Metabolism. West Publishing Company, New York, 1995.
  • Hunter D, et al. A randomized controlled trial of vitamin D supplementation on preventing postmenopausal bone loss and modifying bone metabolism using identical twin pairs. Journal of Bone and Mineral Research 2000; 15:2276-2283.
  • Lininger SW, et al. A-Z guide to drug-herb-vitamin interactions. Prima Health, Rocklin, CA, 2000.
  • Lipkin M, Newmark HL. Vitamin D, calcium and prevention of breast cancer: A review. Journal of the American College of Nutrition 1999; 18(5):392S-397S.
  • Lipkin M, Reddy B, et al. Dietary factors in human colorectal cancer. Ann Med 1994;26:443-52.
  • Lips P, et al. Vitamin D supplementation and fracture incidence in elderly persons. Ann Intern Med 1996; 124:400-406.
  • Pizzorno J, Murray M. The Textbook of Natural Medicine. The Textbook of Natural Medicine.

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