ACS :: Vitamin D

Other common name(s): the sunshine vitamin, calcitriol, calciferol, ergocalciferol (vitamin D2), cholecalciferol (vitamin D3), 1,25-D

Scientific/medical name(s): 1,25 dihydroxycholecalciferol; 1,25 dihydroxyvitamin D

Vitamin D is an essential vitamin the body needs to regulate the amount of calcium and phosphorus in the body. It is best known for its role in using calcium to help build bones and keep them strong. Vitamin D affects many other tissues of the body, including the kidneys, intestines, and parathyroid glands. It is found in salmon, mackerel, tuna, and sardines, as well as in cod liver oil. Most of the milk supply in the United States has vitamin D added to it, as do some breakfast cereals, orange juices, and milk substitutes (such as soy milk). Some experts note that vitamin D acts more like a hormone than a vitamin, in part because the body can make its own vitamin D if the skin gets enough ultraviolet (UV) rays from sunlight.

Vitamin D is needed to keep a balance between calcium and phosphorus in the body by controlling how much of these nutrients are absorbed from foods or taking them from bones when needed. While known for its role in building bones and keeping them strong, the exact function of vitamin D in other cells and organs is not fully known.

After fairly brief exposure to sunlight, the body can make vitamin D for several hours afterward. However, the amount of sun it takes to make enough vitamin D depends on several factors (see "What does it involve?"). Because UV light exposure is linked to skin cancer and other diseases, safety is a concern when considering the use of sunlight to meet vitamin D requirements. Most people can meet their vitamin D requirements through dietary sources and supplements, if used properly. Foods and vitamin D supplements have the added benefit of not causing cancer and other negative skin effects that can result from exposure to UV light.

Although some studies have found that cancer risk is lower for people who have higher levels of vitamin D in the body, more studies are needed to find out whether vitamin D is the reason for this decreased risk. If there is a link, researchers would still have to determine whether vitamin D deficiency raises a person’s cancer risk and/or whether intake of vitamin D above the recommended daily value has a protective effect. The possible role of vitamin D in treating cancer is still being studied.

Vitamin D is promoted mainly for its role in balancing calcium and phosphorus and keeping bones healthy. Some practitioners claim that vitamin D is an immune system booster that can be used to prevent many problems, including autism, type I diabetes, schizophrenia, mood disorders, infectious diseases, cancer, and other illnesses. Others say it is helpful for weight loss. In orthomolecular medicine and some other forms of alternative medicine, large doses of vitamin D may be used along with other vitamins to treat cancer (see Orthomolecular Medicine). Vitamin D is also being studied as a component of conventional treatment regimens together with chemotherapy.

The body can make vitamin D after exposure to UV rays or it can be obtained through some foods or supplements. The amount of vitamin D made when the skin is exposed to sunlight depends on several factors, including skin color, age, how much skin is exposed, time of year, time of day, cloud cover, length of exposure, and geographic location. Latitudes further away from the equator do not get much UV light through earth's atmosphere in the winter months. This can be a problem for people who live in the northern United States and Canada and who do not take in much vitamin D in foods. In addition, darker-skinned people need somewhat longer UV exposures to trigger their bodies to make vitamin D, and older people do not make as much vitamin D as younger people in response to sunlight. Sunscreen also blocks UV rays, which reduces the body's ability to produce vitamin D.

Even in a sunny climate, sunlight's effects can be hard to predict. One study looked at 93 adults in Hawaii who reported several hours of sun exposure each week for at least 3 months. The researchers found that half of them had low vitamin D levels in their blood. Closer analysis showed no link between vitamin D levels and age, lightest or darkest skin colors, or hours of sun exposure without sunscreen. Clearly, there is no "one size fits all" prescription for a reliable minimum amount of sun exposure to meet the vitamin D requirements of every person.

The body stores several forms of vitamin D. Vitamin D3 is the form that is made in the skin. Vitamin D2 (calciferol) or D3 (cholecalciferol) can be absorbed from food. All must be changed into 25 hydroxyvitamin D (25 hydroxycholecalciferol), a form that can last for several weeks in the blood. This is the vitamin D level that doctors generally check. The liver and kidneys change vitamin D into calcitrol (also called 1,25 dihydroxycholecalciferol or 1,25 dihydroxyvitamin D), which helps the intestine absorb more calcium and phosphorus.

After a review of evidence in the 1990s, the Institute of Medicine concluded that there was not enough scientific evidence to set a recommended daily allowance (RDA) for vitamin D. They were able to decide on an adequate intake (AI), which is a less definitive level. The AI of vitamin D for infants, children, and men and women up through age 50 is 200 International Units (IU) per day (equal to 5 micrograms). Adequate intake is 400 IU per day (10 micrograms) for adults aged 51 to 70 and 600 IU a day (15micrograms) for adults older than 70. The safe upper limit for adults was set at 2,000 IU per day.

New evidence has some nutrition experts suggesting that the recommendations may be too low. Blood tests can now measure the body's stores of vitamin D, and many people have unexpectedly low levels. There is now serious discussion about how much vitamin D it takes to raise the body's stores of it to healthy levels.

Because it does not occur naturally in many foods, many adults may not get enough vitamin D from their everyday diet. The addition of vitamin D to milk and other breakfast foods has helped many people get more of it. For instance, 1 cup of fortified milk contains half of what is currently considered to be the adequate intake (AI) of vitamin D (see below) for an adult between the ages of 19 and 50. That same cup supplies only one-quarter of the AI for an adult aged 51 to 70, and about one-sixth of the AI for a person 71 or older.

deficiency of pancreatic enzymes
Crohn’s disease
cystic fibrosis
sprue or celiac disease (gluten intolerance)
certain types of liver disease
surgical removal of all or part of the stomach or intestine

Vitamin D supplements are most often taken in pill form, although cod liver oil is also still used. Supplements are available at drugstores, grocery stores, health food stores, and on the Internet.

Rickets, a disease of weak bones and other deformities, was first described in the mid-1600s as a major problem among city children. Even though there were reports that rickets could be cured by sunbathing or cod liver oil, the disease was still widespread in northern Europe in the early twentieth century. After vitamin A was discovered in 1913 by Elmer McCollum as a cure for night blindness, a British doctor named Edward Mellanby induced rickets in dogs and then cured the condition using cod liver oil. He assumed that the vitamin A in the cod liver oil had cured the dogs. To test Mellanby's theory, McCollum devised a way to inactivate the vitamin A in cod liver oil. As expected, the oil no longer worked to treat night blindness. To the surprise of nearly everyone, however, it still cured rickets, which proved that another substance besides vitamin A was responsible. McCollum published these findings in 1922, calling this substance vitamin D. Soon after, a program to add vitamin D to milk was started in the United States, and rickets was nearly wiped out. Cod liver oil has remained a home remedy ever since.

Even though vitamin D was named and put to wide use, scientists in the early twentieth century knew almost nothing about what it was or how it worked. It took years of study and discoveries by a number of researchers to learn that there were several forms of vitamin D, and how they work in the body.

German researcher Adolf Windaus first discovered 3 forms of the vitamin, which he called D1, D2, and D3. (Because it was later learned that the product Windaus named vitamin D1 was a mixture of compounds rather than a pure vitamin D product, the term D1 is no longer used.) In the early 1950s, Arvid Carlsson found that vitamin D can remove calcium from the bones when the body needs it for other uses. Ragnar Nicolaysen, a dietary researcher, discovered that the amount of calcium absorbed from food is guided by an internal factor that tells the intestine how much the body needs. In 1975, another researcher named Mark Haussler confirmed that the intestines have a receptor protein that specifically binds to active vitamin D.

Today, vitamin D is still added to most milk sold in the United States, although it is not added to all milk products like cheese and ice cream. Some companies also add it to cereal, soy milk, and orange juice, usually along with calcium. It is now understood that rickets is the product of long-standing and severe vitamin D deficiency, and that milder cases of deficiency may have no symptoms.

Since a few studies in the early 2000s have suggested higher vitamin D intake may be related to lower cancer risk, more studies have begun to look at this possibility.

Laboratory and animal studies and observational epidemiologic studies suggest that higher intake of vitamin D may be linked to lower cancer risk. Observational studies suggest that the risk for cancer is lower in those who get more calcium and vitamin D (which may include vitamin D from foods as well as sunlight). Higher vitamin D levels in the blood have been linked in these studies to lower risk for some types of cancer, especially colorectal cancers. Vitamin D appeared to be a protective factor in a study of more than 3,000 adults (mostly men) who had colonoscopies between 1994 and 1997 to look for polyps or cancer. Those with the highest vitamin D intake were less likely to have advanced cancer. Although this sounds promising, observational epidemiologic studies cannot rule out that other unknown factors may have caused the outcome.

Randomized clinical trials, which are considered much stronger evidence than observational studies, have since been started to more reliably study the role vitamin D may play in cancer prevention. A Women's Health Initiative study published in 2006 put more than 36,000 menopausal women into 2 groups: half got vitamin D with calcium supplements and half got a placebo. After 7 years, the researchers looked at colorectal cancer risk in the 2 groups. Cancer risk was not lower in the group that took vitamin D, but critics noted that the dose given (400 IU per day) may have been too low to make a difference, and that many women were not taking their pills at all. The average vitamin D and calcium intake of the women at the start of the study was also about twice as high as the national average, and close to the doses used in the study. This may have limited the ability of the study to find any differences. Interestingly, colorectal cancer risk was lower in women who had higher levels of vitamin D in their blood at the start of the study. This study is still going on, so a final conclusion has not been reached.

A 4-year study published in 2007 looked at 1,179 healthy women over age 55 who were randomly selected from rural Nebraska. The researchers gave a third of the women 1,400 to 1,500 milligrams of calcium each day. Another third received calcium plus 1,100 IU of vitamin D3 each day, while the rest got a placebo. The women who took calcium and vitamin D had significantly less risk for all types of cancer, as did the women who had higher vitamin D levels when the study started. As this was only one study, it is difficult to be certain the vitamin D and calcium caused the difference. It is still possible that other differences between the groups may have accounted for the lower cancer rates. Before this information can be used to recommend increased supplements of vitamin D and calcium, it needs to be confirmed by other studies. It also needs to be shown that the findings hold true in other groups of people, that the supplements don't increase the risk of other problems, and that there are no unexpected side effects.

Additional well-designed clinical trials need to be done to confirm whether low levels of vitamin D raise cancer risk and to determine whether taking more vitamin D (with or without extra calcium) reduces cancer risk. Until such studies are completed, it is too early to advise people to take vitamin D supplements for cancer prevention.

Some researchers are interested in whether vitamin D can play a role in cancer treatment. Some small studies have looked at vitamin D along with standard treatment for prostate cancer. In one study of 16 men with metastatic prostate cancer, 1 in 4 had less bone pain and 1 in 3 had stronger muscles after taking 2,000 IU of vitamin D each day for 12 weeks. However, nearly half of the patients were deficient in vitamin D at the start of the study, which could have affected the results.

Another study looked at the effects of vitamin D3 on blood levels of prostate-specific antigen (PSA) in men whose prostate cancer had recurred after treatment. PSA is a substance produced by normal and cancerous prostate cells, and increased levels are considered to be an indicator of cancer growth. After treatment with radiation or surgery, the men took daily doses of vitamin D3 for a period of between 6 and 15 months. The researchers observed that in 6 of 7 patients, their PSA levels increased more slowly than their pretreatment rate. However, the men began to lose calcium in their urine, which limited the amount of vitamin D they could safely take. This was a small pilot study that called for further testing.

A 2003 study of 22 men with recurrent prostate cancer used larger weekly doses of vitamin D3. The researchers observed that the weekly dose was safe. However, while the rate of PSA increase in men slowed to some extent, more studies are needed to determine whether vitamin D has a significant role in slowing the growth of prostate cancer.

Women who are vitamin D–deficient give birth to children with very little vitamin D in their bodies. In addition, past measurements have indicated that human breast milk contains very little vitamin D, leading to the recommendation that infants fed only breast milk be given vitamin D supplements. However, recent small early studies in breast-feeding women have found that women with high blood levels of vitamin D have adequate amounts in their breast milk. In order to reach these levels, though, researchers had to give the women very high doses of vitamin D each day. More research is needed to find out about safety and side effects, use of blood levels to determine vitamin D status, and optimum blood levels of the vitamin.

Results of an observational epidemiologic study presented at the 2008 annual meeting of the American Society of Clinical Oncology suggest that breast cancer patients with vitamin D deficiency do not live as long as those with adequate vitamin D status.

Researchers are also testing whether vitamin D can increase the effectiveness of some chemotherapy drugs. Although preclinical studies and preliminary human studies in prostate cancer were encouraging, a 2008 report of a randomized, double-blinded clinical trial did not indicate that taxotere plus vitamin D was any more effective than the chemotherapy drug alone in prolonging the lives of men with advanced prostate cancer.

Researchers are also testing deltanoids—compounds chemically related to vitamin D—for cancer prevention and for treatment, alone and in combination with other conventional drugs.

Vitamin D can prevent and treat some bone problems such as rickets in children and osteomalacia in adults. Vitamin D deficiency, which is often seen in older people, can lead to osteoporosis and is linked to an increased risk for broken hips. Studies of the effect of vitamin D supplements on hip fracture risk among older people have had conflicting results. More information is needed before any recommendations can be made for older people at risk of hip fracture.

A vitamin D derivative was proven to be effective at reducing the symptoms of the skin condition psoriasis.

Although low vitamin D levels seem to be linked to several diseases, further study is needed to learn whether the disease causes the low levels of vitamin D, the vitamin deficiency increases the risk for disease, or there is some other relationship between the two.

This product is sold as a dietary supplement in the United States. Unlike companies that produce drugs (which must provide the FDA with results of detailed testing showing their product is safe and effective before the drug is approved for sale), the companies that make supplements do not have to show evidence of safety or health benefits to the FDA before selling their products. Supplement products without any reliable scientific evidence of health benefits may still be sold as long as the companies selling them do not claim the supplements can prevent, treat, or cure any specific disease. Some such products may not contain the amount of the herb or substance that is written on the label, and some may include other substances (contaminants). Though the FDA has written new rules to improve the quality of manufacturing processes for dietary supplements and the accurate listing of supplement ingredients, these rules do not take full effect until 2010. And, the new rules do not address the safety of supplement ingredients or their effects on health when proper manufacturing techniques are used.

Most such supplements have not been tested to find out if they interact with medicines, foods, or other herbs and supplements. Even though some reports of interactions and harmful effects may be published, full studies of interactions and effects are not often available. Because of these limitations, any information on ill effects and interactions below should be considered incomplete.

Vitamin D is considered safe as part of a normal healthy diet. Too much vitamin D can cause nausea, vomiting, poor appetite, constipation, weakness, and weight loss. It can also raise blood calcium levels, causing changes in mental status such as confusion. High blood calcium can also cause abnormal heart rhythms. Too much vitamin D over a long time can cause depression, headaches, sleepiness, and weakness, as well as calcium and bone loss. It can also cause the arteries and other soft tissues of the body (such as kidneys, heart, lungs) to become hardened and lined with layers of calcium, a condition known as calcinosis.

Getting vitamin D through sunlight may not work for some and may cause problems for others. In addition to the immediate danger of sunburn, exposure to ultraviolet light can cause skin cancer; wrinkled, sagging skin; damage to the eyes, including cataracts; and can impair the immune system. Reflective surfaces make UV exposure more intense and can worsen these effects. Water, snow, and sand reflect the most. While sun exposure can cause other problems, it has never been reported to produce toxic levels of vitamin D. Vitamin D from foods is also unlikely to cause toxicity unless large amounts of cod liver oil are used. Vitamin D toxicity is much more likely to occur as a result of taking too many supplements. Vitamin D toxicity has also been caused by foods that were incorrectly fortified (foods or milk that had accidentally been mixed with far more vitamin D than intended).

Laxatives, steroids, and anti-cholesterol drugs like cholestyramine (Questran, Locholest) and colestipol (Colestid) may lower the amount of vitamin D you can absorb. Vitamin D should be taken several hours before or after these drugs. Anti-seizure drugs and rifampin (an anti-tuberculosis drug) can lower your vitamin D levels. Too much vitamin D may raise calcium levels, which can cause abnormal heart rhythms if you are taking digoxin.

If you take vitamin D with calcium, note that calcium can keep certain drugs from being absorbed. Always talk with your doctor and pharmacist about all the herbs, supplements, and medicines you are taking. Relying on this type of treatment alone and avoiding or delaying conventional medical care for cancer may have serious health consequences.

The following information on complementary and alternative therapies may also be helpful to you. These materials may be found on our Web site (www.cancer.org) or ordered from our toll-free number (1-800-ACS-2345).

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Chapuy MC, Pamphile R, Paris E, Kempf C, Schlichting M, Arnaud S, Garnero P, Meunier PJ. Combined calcium and vitamin D3 supplementation in elderly women: confirmation of reversal of secondary hyperparathyroidism and hip fracture risk: the Decalyos II study. Osteoporos Int. 2002;13:257-264.

de Sevaux RGL, Hoitsma AJ, Corstens FHM, Wetzels JFM. Treatment with vitamin D and calcium reduces bone loss after renal transplantation: A randomized study. J Am Soc Nephrol. 2002;13:1608-1614.

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EXCITE: Skin Cancer Module: Practice Exercises. Centers for Disease Control and Prevention Web site. http://www.cdc.gov/excite/skincancer/mod06.htm. Updated August 27, 2004. Accessed August 6, 2007.

Goodwin PJ, Ennis M, Pritchard KI, Koo J, Hood N. Frequency of vitamin D (Vit D) deficiency at breast cancer (BC) diagnosis and association with risk of distant recurrence and death in a prospective cohort study of T1-3, N0-1, M0 BC. J Clin Oncol. 2008;26 (May 20 supplement; abstract 511).

Grant AM, Avenell A, Campbell MK, McDonald AM, MacLennan GS, McPherson GC, Anderson FH, Cooper C, Francis RM, Donaldson C, Gillespie WJ, Robinson CM, Torgerson DJ, Wallace WA; RECORD Trial Group. Oral vitamin D3 and calcium for secondary prevention of low-trauma fractures in elderly people (Randomised Evaluation of Calcium Or vitamin D, RECORD): a randomised placebo-controlled trial. Lancet. 2005;365:1621-1628.

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Hollis BW, Wagner CL. Assessment of dietary vitamin D requirements during pregnancy and lactation. Am J Clin Nutr. 2004:79: 717-726.

Jackson RD, LaCroix AZ, Gass M, Wallace RB, Robbins J, Lewis CE, Bassford T, et al. Women's Health Initiative Investigators. Calcium plus vitamin D supplementation and the risk of fractures. N Engl J Med. 2006;354:669-683.

Lappe JM, Travers-Gustafson D, Davies KM, Recker RR, Heaney RP. Vitamin D and calcium supplementation reduces cancer risk: results of a randomized trial. Am J Clin Nutr. 2007;85:1586-1591.

Porthouse J, Cockayne S, King C, Saxon L, Steele E, Aspray T, et al. Randomised controlled trial of calcium and supplementation with cholecalciferol (vitamin D3) for prevention of fractures in primary care. BMJ. 2005;330:1003.

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Wactawski-Wende J, Kotchen JM, Anderson GL, Assaf AR, Brunner RL, Langer RD, Lasser NL, Lewis CE, Limacher MC, Manson JE; Women's Health Initiative Investigators. Calcium plus vitamin D supplementation and the risk of colorectal cancer. N Engl J Med. 2006;354:684-696.

Wagner CL, Hulsey TC, Fanning D, Ebeling M, Hollis BW. High-dose vitamin d(3) supplementation in a cohort of breastfeeding mothers and their infants: a 6-month follow-up pilot study. Breastfeed Med. 2006;1:59-70.

Weaver CM, Fleet JC. Vitamin D requirements: current and future. Am J Clin Nutr. 2004;80:1735S-1739S.

Note: This information may not cover all possible claims, uses, actions, precautions, side effects or interactions. It is not intended as medical advice, and should not be relied upon as a substitute for consultation with your doctor, who is familiar with your medical situation.

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