vitamin D

What Is It?
Health Benefits
Recommended Intake
If You Get Too Little
If You Get Too Much
General Dosage Information
Guidelines for Use
General Interaction
Evidence Based Rating Scale

What Is It?

Vitamin D3 (cholecalciferol) is called the sunlight vitamin because the body produces it when the sun's ultraviolet B (UVB) rays strike the skin. Technically considered a Hormone, it is the only vitamin the body manufactures naturally. Vitamin D is essential for building strong bones and teeth, and it also helps to strengthen the immune system, improving resistance to infections and possibly preventing some types of cancer.

While just 10 to 15 minutes of skin exposure to the summer sun without sunscreen a few days a week supplies adequate amounts of vitamin D3, those who can't get out in the sun frequently need a supplement. In winter, people in northern climes who don't get enough sun also need additional amounts of the vitamin. Unfortunately, the body's ability to manufacture vitamin D3 appears to decline with age, so older adults may need to get more vitamin D3 through diet (fortified milk and fatty fish have good amounts) or supplements, even if they're exposed to sunlight.

Surprisingly, even younger adults may have inadequate stores of this nutrient: in one study involving almost 300 patients of varying ages who were hospitalized for different types of ailments, 57% were found to have low levels of vitamin D. (1) Because deficiency seems to be much more common than previously thought, adults are encouraged to request that a vitamin D blood level (25 hydroxy D) be checked as part of their general health maintenance. Although most laboratories report that levels of 30.0 to 74.0 nanograms per milliliter (ng/mL) are normal, humans well exposed to ultraviolet light have levels up to 88 ng/ml, suggesting that higher levels are optimal. (50) When levels are below 50-60 ng/ml, integrative medicine physicians generally recommend short-term use of treatment doses, which are usually higher than recommended daily supplement doses.

Another form of the vitamin, vitamin D2 (ergocalciferol), is a synthetic version made from the plant sterol ergosterol and yeast. Both ergocalciferol and cholecalciferol require chemical reactions in the body to form the active form of vitamin D, calcitriol. Both forms of vitamin D seem to be well absorbed by the body, but the synthetic forms have been shown to have only one third the potency of D3 and are potentially more toxic than cholecalciferol. 

Health Benefits

By promoting the absorption and balance of calcium and phosphorous in the body, vitamin D strengthens the bones and teeth and also fosters normal muscle contraction and nerve function. It is also useful for promoting immunity and blood cell formation. In addition, Vitamin D supplements may slow the growth of or even prevent some cancers.

Specifically, vitamin D may help to:

Prevent osteoporosis. The body cannot absorb calcium from food or supplements without an adequate intake of vitamin D. If calcium levels in the blood are too low, the body will steal the Mineral from the bones in order to supply the muscles and nerves with the amount they need. Over time, the loss of calcium in the bones can lead to osteoporosis, a disease in which bones become porous and prone to fractures. A considerable experimental and epidemiologic body of evidence supports the need for calcium and vitamin D supplementation to reduce the risk of fracture and osteoporosis. After menopause, women are particularly at risk for developing this condition. Vitamin D3 taken along with calcium plays a critical role in maintaining bone density. In a Tufts University study of 176 men and 213 women over age 65, those who took 500 mg of calcium and 700 IU of vitamin D3 daily for three years experienced a decrease in bone density loss. (2) Moreover, the incidence of fractures was cut in half. In another study, of 3,270 healthy elderly French women, a daily dietary supplement of 1,200 mg calcium plus 800 IU of vitamin D3 lowered the incidence of hip fractures by 43% in just two years. (3) In another large-scale study of more than 36,000 postmenopausal women (The Women's Health Initiative) aged 50 to 79, researchers set out to test the effects of taking 1,000 mg of calcium plus 400 IU of vitamin D3 daily for seven years, but adherence to the program was low. In women who were at least 80% adherent, treatment significantly reduced the risk of hip fractures by about 29%; women who did not adhere to the program showed only modest improvement in bone mineral density and no reduced risk of fracture. (4) Several more studies found that a daily dose of 800 IU of vitamin D3, or 100,000 IU given three times a year, reduced the frequency of both falls and fractures. (5-8) A number of other diseases, including inflammatory bowel disease, epilepsy, and others, increase the risk of osteoporosis either due to calcium malabsorption or to the adverse effects of drugs such as corticosteroids. Persons with chronic diseases should be especially cautious about osteoporosis prevention including checking vitamin D levels.

Protect against certain types of cancer. A number of studies indicate that low vitamin D levels are associated with a variety of cancers and supplementation may be useful in preventing or augmenting treatment, especially for cancers of the breast, colon, and prostate. (9-14) A prospective cohort study of the effect of vitamin D3 supplementation in cancer incidence and mortality found that men with the highest level of vitamin D had a 17% reduction in overall cancer incidence, 29% reduction in cancer-related mortality, 43% reduction in gastrointestinal cancer incidence, and 45% reduction in gastrointestinal cancer-related mortality. (15) Another population-based trial of healthy postmenopausal women found those who took 1,400 to 1,500 mg of supplemental calcium plus 1,100 IU of vitamin D3 daily had a 60% lower relative risk of developing all types of cancer. (16) However, in another study, higher vitamin D serum levels were only associated with a reduced risk of mortality related to colon cancer and not to other types. (17)Studies have shown that men with colon cancer have lower blood levels of vitamin D than those who do not have the disease. In addition, men with the highest intake of vitamin D are less likely to get colon cancer. A 19-year prospective study of 1,954 Chicago men showed that higher intake of vitamin D was associated with a significant reduction in the risk for colon cancer. (18) A 2009 study involving 1,225 patients with colon cancer, 728 patients with rectal cancer, and 4,154 control patients also found an inverse relationship between increased dietary vitamin D intake and colon cancer risk. While increased vitamin D intake appeared to be unrelated to rectal cancer, patients with the highest vitamin D intake levels showed the lowest risk of developing colon cancer. (19) 

Slow joint damage due to arthritis. Population research from 1994 suggests that older women who have a higher intake of vitamin D from foods or supplements tend to have a lower risk of developing rheumatoid arthritis. (20) For osteoarthritis, recent studies have found vitamin D levels do not affect occurrence of new cases. A 2007 study found vitamin D status was unrelated to the risk of joint space narrowing or Cartilage loss in osteoarthritis (OA) of the knee. (21) However in a 2009 report, 353 randomly selected men and women who had been studied for serum levels of vitamin D, sunlight exposure and cartilage loss were re-studied three years later. At follow up, sunlight exposure and serum vitamin D levels were positively associated with decreased knee cartilage loss, even in patients with OA and knee pain, which suggests that correcting vitamin D levels may prevent and/or slow cartilage loss in patients with OA. (22) More research is needed.  

Ease back pain. Individuals who are prone to back problems may benefit from taking vitamin D3 because of its ability to promote strong bones and cartilage. A 2009 review of six case studies involving the use of vitamin D3 to treat chronic back pain after failed back surgery found correcting vitamin D deficiencies improved quality of life and, in some cases, gave complete resolution of symptoms. (23) Larger studies are needed to confirm or refute efficacy.  

Protect against multiple sclerosis. Preliminary animal research has shown a possible connection between high vitamin D levels and decreased incidence of this disabling nerve disorder, fueling research in the area. This hypothesis may explain why both in the tropics (where there is ample sun to boost vitamin D levels) and in coastal Norway (where sun is scarce, but fatty fish rich in this nutrient abound and are eaten by the local population), cases of MS are rare. In a population study, women who were found to have the highest vitamin D intake via supplements (400 IU or higher per day) were found to be 40 percent less likely to have MS than women not taking vitamin D supplements. (24, 25) Additional population research in over 7 million people showed that higher blood levels of vitamin D are associated with significantly lower risk of developing MS. In white men and women, for every 50 nmol/L increase in 25-hydroxyvitamin D levels (the specific blood test for vitamin D), there appears to be a 41 percent decrease in MS risk; however the risk reduction was not apparent in black and Hispanic men and women. (26) Another small study found an increased protective effect of high levels of vitamin D only in women. (27) More research is needed. 

Relieve the symptoms of psoriasis. Because it plays a role in skin cell metabolism and growth, vitamin D may be helpful in treating the itching and flaking associated with this chronic skin ailment. A few studies show that individuals with psoriasis have low blood levels of vitamin D. Over-the-counter vitamin D creams and supplements have little effect on psoriasis. However, studies do show that the active form of vitamin D3, called calcitriol (1,25 dihydroxycholecalciferol), which is available only by prescription in cream and supplement form, may be useful for psoriasis. It is thought to work by helping skin cells to replicate normally. (28-30) In two randomized, double-blind clinical trials, 3 mcg/g calcitriol ointment applied twice daily for eight weeks resulted in clearing or minimal residual psoriasis in 34% of patients, compared with 12% - 22.5% of patients treated with vehicle ointment. In patients treated with calcitriol ointment for a year or longer, treatment led to sustained improvement in the severity of psoriasis and was well tolerated by patients. (31)  

Reduce risk of cardiovascular disease. Preliminary population research indicates that people with lower vitamin D levels are significantly more likely to have cardiovascular disease risk factors including type 2 diabetes, obesity, hypertension, and high cholesterol, compared to people with higher vitamin D levels. (32-35) However, there is no reliable evidence that taking vitamin D supplements can prevent cardiovascular disease. In the Women's Health Initiative, taking 200 IU of vitamin D (cholecalciferol) plus 500 mg of calcium twice daily did not significantly reduce the risk of cardiovascular events such as heart attack or stroke; however this dose may have been too low to make a difference. (36) More research is needed to determine whether vitamin D deficiency is a cause or consequence of poor cardiovascular health and whether supplementation can reduce mortality and cardiovascular diseases.  

Prevent melanoma. The risk of sunlight exposure and incidence of melanoma (skin cancer) is highly controversial among researchers. Several studies have shown that non-sun-exposed areas of the skin have a higher incidence of melanoma, including malignant melanoma, than sun-exposed areas. (37-39) A large epidemiologic study of U.S. Navy personnel found that adequate vitamin D levels may decrease the chance of development of melanomas in some adults. (40) More research is needed to confirm the role of vitamin D supplementation in preventing melanoma. To reduce the risk of developing UV-induced skin cancers (including basal and squamous cell cancers in addition to melanoma) from excess sun exposure, a review of studies indicates that taking 1,000 to 2,000 IU of vitamin D3 daily help to protect against vitamin D-deficiency. (41)

Protect against influenza. Because the onset of the "flu season" corresponds to the time of year when people have the least sun exposure, nutritional physicians have begun to wonder if vitamin D deficiency predisposes people to getting the flu. British researcher Edgar Hope-Simpson first documented the seasonality of epidemic influenza in the 1960s (after he became famous for discovering the cause of shingles), but he did not identify the specific factor involved. Researchers later hypothesized that vitamin D is the "seasonal factor" responsible for triggering flu epidemics, supported by evidence that vitamin D boosts the immune system, protects against infection and inhibits inflammation. The main study involved patients of a mentally ill hospital ward who were quarantined during an influenza epidemic in 2005. The quarantined patients had been taking 2,000 IU of vitamin D3 daily for several months or longer and did not contract the flu, while patients in the other wards around the quarantined patients were battling the epidemic. (42-44) These preliminary studies have warranted further research into the efficacy of vitamin D to boost immunity in preventing and treating seasonal flu.


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Recommended Intake

The government goals for the daily intake of Vitamin D for men and women follow. They are lower than some integrative medicine sources recommend.  Called AI (Adequate Intake), the figures supplant the old RDA (Recommended Daily Allowance) and represent the minimum amount of daily Vitamin D that all individuals in the following age groups should try to meet.

--For men and women ages 19 to 50: 200 IU a day.

--For men and women ages 51 to 70: 400 IU a day.

--For men and women ages 71 and older: 600 IU a day.

For more information on Adequate Intake and other dietary guidelines, see Government Dietary Guidelines. However, optimal dosing of vitamin D is controversial. Reputable nutritional scientists have criticized the government guidelines as being inadequate to deal with the epidemic of Vitamin D deficiency in the US and Europe. (45, 46)

If You Get Too Little

Insufficient amounts of vitamin D can lead to the development of osteoporosis in adults. Other signs of a deficiency are nervousness, muscle twitches, insomnia, and diarrhea.

In children, a severe deficiency can cause a bone-weakening disease called rickets. Today it is rare to see a child with rickets in industrialized countries because milk is fortified with vitamin D. Moreover, most children get enough exposure to sunlight for their bodies to manufacture all the vitamin D that they need.

If You Get Too Much

Doses greater than 2,000 IU a day of vitamin D3 are not generally recommended without the guidance of a health care professional. Signs and symptoms of a toxic reaction include loss of appetite, headache, nausea, vomiting, diarrhea and excessive thirst and urination. While taking up to 10,000 IU daily appears to be safe for most people (46, 47), taking 50,000 IU a day regularly can give toxic blood levels and could cause weight loss, paleness, constipation, fever, and a number of serious complications. Long-term over-consumption of vitamin D supplements may cause high blood pressure and premature hardening of the arteries. Bones may weaken and a calcium buildup in muscles and other soft tissues may occur. Kidney damage may also develop.

General Dosage Information

Special tips: Getting 10 to 15 minutes of sunlight on your face, hands, and arms between 8 A.M. and 3 P.M. two or three times a week may supply the vitamin D you need in the summertime or at any time if you live to the south of Atlanta and San Francisco. However, some people stay deficient even with sun exposure (48). You should consider taking a supplement if you are over age 50; rarely go outdoors at midday; or always wear sunscreen (the skin manufactures vitamin D under the influence of the sun's ultraviolet B rays).

--If you need to take a supplement for any of the reasons noted above, many experts advise taking more than the government-recommended intake as long as it does not exceed 2,000 IU a day. The best advice is to get your blood levels measured by age 35 as part of general health checkup, or if you have any chronic illness or a family history of cancer, diabetes, osteoporosis, or heart disease.

  • For arthritis: 2000 IU daily.

  • For back pain: 2000 IU daily has been used.

  • For preventing cancer: 1000 IU daily.

  • For preventing heart disease: 1000 IU of vitamin D daily in combination with 1000 mg calcium.

  • For preventing influenza: 1000 to 2000 IU daily has been used.

  • For preventing multiple sclerosis: 400 to 1000 IU daily has been used.

  • For preventing and treating osteoporosis: 2000 IU daily has been in combination with 600 mg calcium twice a day.

  • For treating psoriasis: 3 mcg/g calcitriol ointment applied twice daily has been used.

  • For reducing risk of rheumatoid arthritis: 1000 IU/day

Be sure to check out our Dosage Recommendations Chart for vitamin D, which lists therapeutic dosages for specific situations at a glance.

Guidelines for Use

  • To promote absorption, take this Fat-soluble vitamin with food that contains some fat.

  • When selecting a dose of supplemental vitamin D, consider what is already in your daily multivitamin. Most contain up to 400 IU of this vitamin. When possible, choose D3 rather than D2.

  • The doses suggested are for general health maintenance and prevention. Substantially higher doses may be needed on a short-term basis to raise blood levels of vitamin D that are too low.

  • The “normal” vitamin D range in laboratory reports has not kept up with what integrative physicians consider to be healthy levels. Appropriate levels may continue to be adjusted over the next few years. For more information, visit 

General Interaction

  • Because Vitamin D enhances absorption of a number of minerals, high dose Vitamin D supplements should not be combined with antacids containing magnesium or aluminum.

  • Vitamin D stimulates the Cytochrome P450 system responsible for liver metabolism of a number of drugs including oral contraceptives and atorvastatin (Lipitor) for lipid lowering. More rapid metabolism may cause these kinds of drugs to be less effective. Check with your doctor if there is any question.

  • When taken with thiazide diuretics, such as hydrochlorothiazide, vitamin D could cause excessive buildup of calcium levels in the body. Blood calcium levels should be monitored when using this combination.

  • Calcium is involved in regulation of heart muscle contraction. Persons taking drugs for arrhythmia along with vitamin D supplementation should have blood calcium levels monitored. 

Note: For information on interactions with specific drugs, see our WholeHealthMD Drug/Nutrient Interactions Chart.


Patients with kidney disease should use vitamin D only as directed by their nephrologist as the use and monitoring of other related hormone and mineral levels is very complex. 

Women who are pregnant or breast-feeding should take no more than 800 IU of vitamin D daily. Higher doses during pregnancy may cause birth abnormalities. Ask your obstetrician to measure your Vitamin D levels and supplement accordingly. 

The body efficiently eliminates any extra vitamin D it makes from sunlight. However, toxic reactions--some of them quite serious--can occur with extended use of high doses. Only use more than 2000 IU/day under physician guidance.  


1. Thomas MK, Lloyd-Jones DM, Thadhani RI, et al. Hypovitaminosis D in medical inpatients. N Engl J Med. 1998 Mar 19;338(12):777-83.
2. Dawson-Hughes B, Harris SS, Krall EA, Dallal GE. Effect of calcium and vitamin D supplementation on bone density in men and women 65 years of age or older. N Engl J Med. 1997;337:670-6.
3. Chapuy MC, Arlot ME, Duboeuf F, Brun J, et al. Vitamin D3 and calcium to prevent hip fractures in the elderly women. N Engl J Med. 1992 Dec 3;327(23):1637-42.
4. Jackson RD, LaCroix AZ, Gass M. Calcium plus vitamin D supplementation and the risk of fractures. N Engl J Med. 2006;354:669-83.
5. Rodriquez-Martinez MA, Garcia-Cohen EC. Role of Ca and vitamin D in the prevention and treatment of osteoporosis. Pharmacol Ther. 2002;93:37-49.
6. Mezquite RP, Munez TM, Rodriquez LF, et al. Prevalence of vitamin D deficiency in populations at risk for osteoporosis: impact on bone integrity. Med Clin (Barcelona). 2002;119:85-89.
7. Lilliu H, Pamphile R, Chapuy MC, et al. Calcium-vitamin D3 supplementation is cost-effective in hip fractures prevention. Maturitas. 2003;44:299-305.
8. Trivedi DP, Doll R, Khaw KT. Effect of four monthly oral vitamin D3 (cholecalciferol) supplementation on fractures and mortality in men and women living in the community: randomized double-blind controlled trial. BMJ 2003;326:469-472.
9. Garland FC, White MR, Garland CF, et al. Geographic variation in breast cancer mortality in the United States: a hypothesis involving exposure to solar radiat

Date Published: 04/19/2005
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