Vitamin D

Definition

Vitamin D is an essential fat-soluble micronutrient produced in the human body from the action of the sun's ultraviolet (UV) rays on the skin and also obtained from a few foods or from dietary supplements.

Purpose

Vitamin D regulates the body's absorption and retention of calcium and phosphorus, which are essential for building bone. Calcium is also involved in muscle contractions and nerve impulse transmission. There are cell receptors for vitamin D throughout the body, and many genes that regulate cell proliferation, differentiation, and apoptosis (cell death) are affected by vitamin D. Although scientists are still trying to understand all of the remarkable roles that vitamin D fulfills in the human body, it is well known that it targets the intestines, kidneys, and bones. It is also thought to play roles in brain, pancreas, skin, parathyroid, and reproductive health, and in controlling cell growth, reducing inflammation, and supporting the immune system to ward off diseases.

Vitamin D

Age

Recommended dietary allowance

Tolerable upper intake level

Children 0-6 mos.

400 IU

10 μg

1,000 IU

25 μg

Children 6-12 mos.

400 IU

10 μg

1,520 IU

38 μg

Children 1-3 yrs.

600 IU

15 μg

2,520 IU

63 μg

Children 4-8 yrs.

600 IU

15 μg

3,000 IU

75 μg

Children 9-18 yrs.

600 IU

15 μg

4,000 IU

100 μg

Adults 19-50 yrs.

600 IU

15 μg

4,000 IU

100 μg

Adults 51-70 yrs.

600 IU

15 μg

4,000 IU

100 μg

Adults 71 ≥ yrs.

800 IU

20 μg

4,000 IU

100 μg

Pregnant women

600 IU

15 μg

4,000 IU

100 μg

Breastfeeding women

760 IU

19 μg

4,000 IU

100 μg

Food

Vitamin D (IU)

Cod liver oil, 1 tbsp.

1,360

Salmon, cooked, 3.5 oz.

360

Mackerel, cooked, 3.5 oz.

345

Tuna, canned in oil, 3 oz.

200

Milk, fortified, 1 cup

100

Orange juice, fortified, 1 cup

100

Cereal, fortified, 1 serving

40

Egg, 1 whole

20

Note: 1 IU equals approximately 0.025 μg

1 IU = International unit

μg = microgram (mcg)

SOURCE: Office of Dietary Supplements. National Institutes of Health. “Vitamin D: Fact Sheet for Health Professionals.” https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional (accessed April 19, 2018).

Description

Vitamin D exists in several forms, two of which are important for humans. Vitamin D2 or ergocalciferol is made by plants and can be produced by irradiating yeast. Vitamin D3 or cholecalciferol is produced in the skin when it is exposed to UV rays in sunlight; when UV rays pass through the skin, they convert 7-dehydrocholesterol to previtamin D3, which is then converted to vitamin D3. Vitamins D2 and D3 are the forms of vitamin D found in dietary supplements and vitamin D-fortified foods. Neither D2 nor D3 is active in the body; rather, they are converted to 25-hydroxyvitamin D—25(OH)D, or calcidiol, in the liver, which is subsequently converted to the active form, 1,25-dihydroxyvitamin D, or calcitriol, in the kidney.

Vitamin D's role in health

The importance of vitamin D for bone health has long been known. Only recently have researchers begun to explore its effects on cell differentiation, the immune system, and other processes.

BONE HEALTH. Vitamin D and calcium are closely connected. The body needs calcium to build bones and teeth, contract muscles, transmit nerve impulses, and help clot blood. Vitamin D helps the body get the calcium it needs by increasing the amount of calcium absorbed in the small intestine.

Vitamin D is an active player in the feedback loop that maintains a normal level of calcium in the blood. To maintain health, the amount of calcium in the blood must stay within a very narrow range. When calcium in the blood falls below normal, the drop is sensed by the parathyroid glands. The parathyroid glands are four separate clusters of specialized cells in the neck. Low blood calcium levels stimulate the parathyroid glands to secrete parathyroid hormone (PTH). PTH travels through the bloodstream and stimulates the kidney to increase production of active vitamin D. Active vitamin D is released into the blood and stimulates the cells lining the small intestine to absorb more calcium from digesting food. Vitamin D also causes the kidneys to conserve calcium so that less is lost in urine. If these activities do not return the level of calcium in the blood to normal, vitamin D activates cells called osteoclasts that break down bone to return calcium to the blood. Thus, people who do not have enough vitamin D absorb less calcium from the food they eat. To make up for this, calcium is taken from their bones, which weaken and break more easily. Thus, vitamin D promotes calcium absorption in the gut and maintains adequate calcium and phosphate concentrations for mineralization of bone. Vitamin D is also required for bone growth and for ongoing bone remodeling by osteoclasts and cells called osteoblasts that form bone.

CANCER PREVENTION AND TREATMENT. Vitamin D is involved in the regulation of cell differentiation. During development, cells divide repeatedly. At some point, they are triggered to specialize (differentiate) into different types of cells, for example, skin, muscle, blood, or nerve cells. Vitamin D works with other compounds to turn on and off more than 50 different genes that halt cell growth and start cell differentiation.

https://www.clinicaltrials.gov .




Bowed legs of a middle-aged man with rickets or osteomalacia, a nutritional deficiency of vitamin D which results in malformation of the skeleton.





Bowed legs of a middle-aged man with rickets or osteomalacia, a nutritional deficiency of vitamin D which results in malformation of the skeleton.
(DR P. MARAZZI/Science Source)

OTHER DISORDERS. Vitamin D has been shown to successfully treat a few other disorders. Psoriasis, a skin disorder, often responds to ointments that contain synthetic vitamin D3 when other treatment options have failed. When the parathyroid glands fail to function or are removed during surgery, vitamin D supplements help to make up for the lack of PTH. Supplements are also used to treat rare inherited familial hypophosphatemia and Fanconi syndrome-related hypophosphatemia. Both of these disorders are characterized by abnormally low levels of phosphate in the blood.

U.S. brand names

U.S. brand-name vitamin D supplements include:

Canadian brand names

Canadian brand-name vitamin D supplements include D-Vi-Sol and Radiostol Forte.

Recommended dosage

Because all of the roles of vitamin D in the human body are not well understood, experts disagree on the amount of vitamin D required. In 2010, the U.S. Institute of Medicine (now the National Academy of Medicine) tripled the vitamin D Recommended Dietary Allowance (RDA) for adults and children aged one year and up to 600 international units (IU), or 15 micrograms (mcg) per day (1 mcg of vitamin D3 equals 40 IU). The RDA is the average daily amount needed to meet the health needs of 97%–98% of people. The RDA for infants under one year is 400 IU. For adults over age 70, the RDA is 800 IU. These RDAs assume that a blood serum level of 50 nmol/L or 20 ng/mL of 25(OH)D is sufficient for bone health in 97% of the population, assuming little sun exposure. The tolerable upper intake level or upper limit (UL) was increased from 2,000 IU to 4,000 IU per day for adults and children over age nine. The UL is 1,000–1,500 for infants and 2,500–3,000 for children aged one through eight. The UL is the average maximum amount that can be taken daily without risking negative side effects. Other authorities argue that many people likely require even more vitamin D for bone health and the prevention of chronic diseases. The National Osteoporosis Foundation recommends that people aged 50 and older get 800–1,000 IU of vitamin D daily.

The 25(OH)D serum concentration reflects both vitamin D produced in the skin and that obtained from food and supplements, although it does not indicate levels of vitamin D stored in body tissues, nor is it known how serum levels relate to health status or outcomes.

Sources of vitamin D
KEY TERMS
1,25-dihydroxyvitamin D (1,25[OH]D)—
Calcitriol; the active form of vitamin D that regulates calcium and phosphate concentrations in the body.
25-hydroxyvitamin D (25[OH]D)—
Calcidiol; the precursor of 1,25-dihyroxyvitamin D.
Cell differentiation—
The process by which stem cells develop into different types of specialized cells such as skin, heart, muscle, and blood cells.
Cholecalciferol—
Vitamin D3; the form of vitamin D formed in the skin from the reaction of cholesterol with sunlight and also found in fish, fish-liver oils, and egg yolks.
Deficiency—
Shortage of a substance, such as a vitamin, that is necessary for health.
Ergocalciferol—
Vitamin D2; the form of vitamin D produced by some plants and fungi and synthesized as a vitamin D supplement.
Fat-soluble vitamin—
A vitamin, such as vitamin D, that dissolves in fat and can be stored in body fat or the liver.
Fortified—
The addition of micronutrients (essential trace elements and vitamins) to food.
Hormone—
A chemical messenger that is produced by one type of cell and travels through the bloodstream to affect a different type of cell.
International unit (IU)—
An agreed-upon standard of physiological activity for a given biological substance such as a vitamin.
Mineral—
An inorganic substance, such as calcium, that is necessary in small quantities for the body to maintain health.
Osteomalacia—
A softening of the bones in adults that is analogous to rickets in children and is caused by prolonged vitamin D deficiency.
Osteoporosis—
A condition occurring in older individuals in which bones decrease in density and become fragile and more likely to break. It can be caused by lack of vitamin D and/or calcium in the diet.
Parathyroid hormone (PTH)—
A hormone that is secreted by parathyroid glands and regulates calcium and phosphorus metabolism in the body.
Percent daily value (%DV)—
The percent of a daily nutrient requirement, such as fiber, in a 2,000-calorie diet that is provided by one serving of a food as listed on food nutrition labels.
Psoriasis—
An autoimmune skin condition marked by the buildup of dried, dead skin cells that form thick scales.
Recommended dietary allowance (RDA)—
Recommended daily allowance; the average amount of a nutrient that should be ingested daily to prevent about 98% of the population from having a nutrient deficiency.
Rickets—
A disease in growing children that is characterized by soft and deformed bones and is caused by the failure to absorb and utilize calcium and phosphorous, usually due to vitamin D deficiency.
Tolerable upper intake level (UL)—
Upper level; the highest daily intake level of a nutrient that is unlikely to cause adverse health effects in almost all individuals in the general population.

Vitamin D is not found in large amounts in many foods. Therefore, since the 1930s, vitamin D has been added to about 99% of all milk and to some breakfast cereals, breads, orange juice, and infant formulas to prevent rickets. In addition, the U.S. Food and Drug Administration (FDA) requires all foods containing olestra, a fat substitute that cannot be absorbed, to be fortified with the fat-soluble vitamins A, D, E, and K. New Nutrition Facts labels on foods that included the actual amounts and updated percent Daily Values (%DV, calculated from RDAs and ULs) of vitamin D and some other nutrients were scheduled for 2018, but the FDA delayed the new labels until 2020 for large food manufacturers and until 2021 for smaller manufacturers.

Precautions

Vitamin D deficiency

Vitamin D deficiency results in rickets in children and osteomalacia in adults. Rickets is a condition in which the bones do not harden due to a lack of calcium. Instead, they remain soft and become deformed. Osteomalacia is a weakening of bones that have been demineralized, with their calcium returned to the blood. Less than 50 nmol/L or 20 ng/mL is considered inadequate for bone and overall health in otherwise healthy individuals. This less severe demineralization can lead to osteoporosis in older adults. Vitamin D deficiency also can cause joint and muscle pain and muscle spasms.

Vitamin D fortification, along with the popularity of daily multivitamins, has greatly reduced the number of people in the United States who are vitamin D deficient. Because breast milk provides only about 25 IU of vitamin D per quart (L), the American Academy of Pediatrics recommends vitamin D supplements beginning no later than two months of age for babies who are fed only breast milk. Institutionalized or homebound people who rarely go outside are also at risk. One study found that 60% of nursing-home residents were vitamin D deficient. Other populations at risk for vitamin D deficiency include people:

QUESTIONS TO ASK YOUR DOCTOR
Vitamin D excess

Recent evidence suggests potential adverse effects from serum 25(OH)D greater than 150 nmol/L or 60 ng/mL. Vitamin D excess in healthy individuals is almost always linked to taking large amounts of vitamin Das a dietary supplement over several months, which can result in high calcium levels in the blood (hypercalcemia). Calcium deposits may develop in the kidneys, blood vessels, heart, and lungs. The kidneys may be permanently damaged and eventually fail. Because the RDAs and ULs for vitamins and minerals are lower for children than for adults, accidental overdose may occur if children take adult vitamins or other dietary supplements.

Side effects

Side effects of excess vitamin D can include:

Interactions

Some medications may increase the available amount of vitamin D in the body. People taking the following types of drugs should not take a vitamin D supplement without consulting their healthcare provider:

Some types of medications may decrease available vitamin D in the body. People taking the following drugs should discuss with their healthcare provider whether a vitamin D supplement is right for them:

Vitamin D also may interact adversely with:

See also Adult nutrition ; Calcium ; Cancer ; Cancer diet ; Childhood nutrition ; Dietary reference intakes (DRIs) ; Dietary supplements ; Minerals ; Osteoporosis diet ; Ovolactovegetarianism ; Senior nutrition ; Veganism ; Vegetarianism ; Vitamins .

Resources

BOOKS

Case, Helen Saul. Orthomolecular Nutrition for Everyone: Megavitamins and Your Best Health Ever. Nashville, TN: Turner, 2017.

Chopra, Sanjiv. The Big Five Simple Things You Can Do to Live a Longer, Healthier Life. New York: Thomas Dunne/St. Martin's, 2016.

Kelly, Laura, and Helen Bryman Kelly. The Healthy Bones Nutrition Plan and Cookbook: How to Prepare and Combine Whole Foods to Prevent and Treat Osteoporosis Naturally. White River Junction, VT: Chelsea Green, 2016.

PERIODICALS

Chen Songcang, Yingxian Sun, and Devendra K. Agrawal. “Vitamin D Deficiency and Essential Hypertension.” Journal of the American Society Hypertension 9, no. 11 (November 2015): 885–901.

Alzaman, Naweed S., B. Dawson-Hughes, J. Nelson, et al. “Vitamin D Status of Black and White Americans and Changes in Vitamin D Metabolites after Varied Doses of Vitamin D Supplementation.” American Journal of Clinical Nutrition 104, no. 1 (July 1, 2016): 205–14.

Boseley, Sarah. “Adding Vitamin D to Food Reduces Deaths, Say Scientists.” Guardian (February 15, 2017): 1.

Hoffmann, Michelle R., Peter A. Senior, and Diana R. Mager. “Vitamin D Supplementation and Health-Related Quality of Life: A Systematic Review of the Literature.” Journal of the Academy of Nutrition and Dietetics 115, no. 3 (March 2015): 406.

Marano, Hara Estroff. “D is for Development.” Psychology Today 50, no. 6 (November/December 2017): 33–34.

Munasinghe, Lalani L., Y. Yuan, N. D. Willows, et al. “Vitamin D Deficiency and Sufficiency among Canadian Children Residing at High Latitude Following the Revision of the RDA of Vitamin D Intake in 2010.” British Journal of Nutrition 117, no. 3 (February 14, 2017): 457–65.

Saggese, Giuseppe, Francesco Vierucci, Annemieke M. Boot, et al. “Vitamin D in Childhood and Adolescence: An Expert Position Statement.” European Journal of Pediatrics 174, no. 5 (May 2015): 565–76.

Wang, Thomas J. “Vitamin D and Cardiovascular Disease.” Annual Review of Medicine 67 (2016): 261.

Zhao, Jia-Guo, X. T. Zeng, J. Wang, et al. “Association Between Calcium or Vitamin D Supplementation and Fracture Incidence in Community-Dwelling Older Adults: A Systematic Review and Meta-Analysis.” Journal of the American Medical Association 318, no. 24 (December 26, 2017): 2466–82.

WEBSITES

Mayo Clinic Staff. “Vitamin D.” MayoClinic. https://www.mayoclinic.org/drugs-supplements-vitamin-d/art-20363792 (accessed May 23, 2018).

MedlinePlus. “Rickets.” U.S. National Library of Medicine, National Institutes of Health. https://medlineplus.gov/ency/article/000344.htm (accessed May 23, 2018).

MedlinePlus. “Vitamin D.” U.S. National Library of Medicine, National Institutes of Health. https://medlineplus.gov/ency/article/002405.htm (accessed May 23, 2018).

Micromedex. “Vitamin D and Related Compounds (Oral Route, Parenteral Route).” MayoClinic. https://www.mayoclinic.org/drugs-supplements/vitamin-d-and-related-compounds-oral-route-parenteral-route/description/drg-20069609 (accessed May 23, 2018).

Micronutrient Information Center. “Vitamin D.” Linus Pauling Institute, Oregon State University. http://lpi.oregonstate.edu/mic/vitamins/vitamin-D (accessed May 23, 2018).

Nutrition Source. “Vitamin D and Health.” Harvard T. H. Chan School of Public Health. https://www.hsph.harvard.edu/nutritionsource/vitamin-d (accessed May 23, 2018).

Office of Dietary Supplements. “Vitamin D: Fact Sheet for Health Professionals.” National Institutes of Health. https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional (accessed May 23, 2018).

ORGANIZATIONS

Academy of Nutrition and Dietetics, 120 S. Riverside Plaza, Ste. 2190, Chicago, IL, 60606-6995, (312) 899-0040, (800) 877-1600, amacmunn@eatright.org, http://www.eatright.org .

Harvard T. H. Chan School of Public Health, 677 Huntington Ave., Boston, MA, 02115, (617) 495-1000, https://www.hsph.harvard.edu .

Linus Pauling Institute, Oregon State University, 307 Linus Pauling Science Ctr., Corvallis, OR, 97331, (541) 737-5075, Fax: (541) 737-5077, lpi@oregonstate.edu, http://lpi.oregonstate.edu .

Office of Dietary Supplements, National Institutes of Health, 6100 Executive Blvd., Rm. 3B01, MSC 7517, Bethesda, MD, 20892-7517, (301) 435-2920, Fax: (301) 480-1845, ods@nih.gov, https://ods.od.nih.gov .

Tish Davidson, AM
Revised by Margaret Alic, PhD

  This information is not a tool for self-diagnosis or a substitute for professional care.