Drug Profile

Vitamin D maintains normal blood levels of calcium and phosphate, both of which are necessary for bone growth and strength. It is available in several foods (see box above), and your body also can produce it in the skin if you are out in the sun. If you eat a well-balanced diet with a variety of healthful foods and spend some time in the sun, you should have all the vitamin D that your body needs.

The Institute of Medicine (IOM), which is tasked with making recommendations on dietary intake of nutrients such as vitamins and minerals, recommends that healthy adults up to age 70 consume 600 international units (IU) of vitamin D daily. For older adults, the recommended daily allowance increases to 800 IU.

In 2010, the IOM reviewed more than 1,000 studies of vitamin D and calcium and found that the only health benefit demonstrated by reliable studies was the well-established benefit to bone health in certain people. (For more information on the IOM’s recommendations, please read our article “Vitamin D and Calcium for Bone Health: Getting the Right Amount.”)[1]

The Medical Letter editors noted that many older adults, “especially those with dark skin, receive inadequate amounts of vitamin D because of limited exposure to sunlight, decreased synthesis of vitamin D in the skin, and decreased absorption and activation of the vitamin.” Older adults who do not drink milk and those without dark skin who do not expose themselves to sunlight may need to take supplements to achieve the appropriate level of vitamin D intake.[2]

One recent randomized, placebo-controlled trial involving more than 2,500 community-dwelling people aged 65–85 years studied the effect of oral vitamin D₃, taken once every four months for five years, on the incidence of fractures. The group getting vitamin D₃ had a significantly lower risk of any first fracture and for a first hip, wrist, forearm or vertebral fracture. This approach seems promising, especially since it costs a fraction of the expensive prescription drugs used to treat osteoporosis.[3]

The Expert Group on Vitamins and Minerals, an advisory committee in the U.K., found the following:

Excess vitamin D may lead to hypercalcaemia [elevated calcium in the blood] and hypercalciuria [increased calcium in the urine]. Hypercalcaemia results in the deposition of calcium in soft tissues, diffuse demineralisation of bones and irreversible renal and cardiovascular toxicity. Moderate levels of vitamin D intake may enhance renal stone formation in predisposed individuals. Data are available from a range of human supplementation studies, but the levels of vitamin D intake at which hypercalcaemia or hypercalciuria occurs vary between studies. Likely reasons for this include differences in populations studied; for example, several of the studies are in older people, a group vulnerable to vitamin D deficiency, while other studies are in younger adults, who are not likely to be vitamin D deficient. Individuals and groups are also likely to differ in their exposure to vitamin D sources other than supplementation, such as consumption of vitamin D–fortified foods and through exposure to the sun.[4]

(The dose used in the study above was 100,000 IU every 120 days, or less than 1,000 IU per day.)[3]

A prospective, randomized, double-blind, placebo-controlled trial looked at postmenopausal women who were given 2,500 IU of oral vitamin D supplementation daily to evaluate whether vitamin D supplementation would reduce cardiovascular risk. The resulting data showed that vitamin D supplementation did not decrease the risk of cardiovascular disease.[5]

The results of a meta-analysis published in the Lancet in October 2013 showed that vitamin D supplementation had only a small overall benefit for bone mineral density in patients without specific risk factors for vitamin D deficiency.[6]

If you use vitamin D supplements without a doctor’s supervision, do not take more than 600 IU per day if you are 70 or younger or 800 IU per day if you are older than 70. Unlike with some other vitamins, your body cannot eliminate excess vitamin D, so the vitamin can accumulate to dangerous, toxic levels if high doses are consumed. This is especially risky for people who take the heart medication digoxin (LANOXIN) because vitamin D increases the adverse effects of digoxin. The signs of vitamin D toxicity are listed below. Vitamin D overdose may cause death as a result of heart, blood vessel or kidney failure.

Taking doses of vitamin D supplements exceeding 800 IU per day also has been shown to increase the risk of falling, which can lead to fractures, head trauma and other injuries.[7]

If your doctor has prescribed vitamin D to prevent low calcium levels, see him or her regularly to check your progress and reduce the risk of adverse effects. Tell your doctor if you are taking a calcium supplement and discuss how to best increase the amount of calcium in your diet.

An article published in the Jan. 9, 2013, issue of the Journal of the American Medical Association (JAMA) cited a rigorous, randomized controlled trial to evaluate the claim that vitamin D supplements benefit osteoarthritis patients. This study found that vitamin D supplements given to people with osteoarthritis of the knee were not effective in relieving knee pain or slowing the damage to the knee joint.

A 2012 randomized controlled trial, also published in JAMA, contradicted the earlier findings from observational studies suggesting that lower vitamin D levels increased the occurrence of upper respiratory infections (URIs), such as the common cold. This trial demonstrated conclusively that vitamin D supplements failed to prevent URIs or limit their duration or severity.

In 2018, the United States Preventive Services Task Force (USPSTF) found that vitamin D supplements did not show a benefit in preventing falls in patients 65 and older but did carry risk of harm. The USPSTF therefore recommended that seniors not take extra vitamin D in order to prevent falls.[8]

In 2019, the New England Journal of Medicine published results of two clinical trials funded by the National Institutes of Health showing that high-dose vitamin D supplementation was not useful for preventing cancer, cardiovascular disease or diabetes.[9],[10]

In 2019, PLoS One published results of a randomized clinical trial showing that use of high-dose vitamin D supplements for four months in patients with low baseline blood levels of vitamin D did not improve muscle strength.[11]

In 2020, JAMA published results of a randomized clinical trial showing that vitamin D supplements in children with asthma and low blood vitamin D levels did not prevent asthma attacks.[12]

In 2020, JAMA published results of another randomized clinical trial showing that vitamin D supplements did not prevent depression or depressive symptoms.[13]

In 2022, Lancet Diabetes and Endocrinology published an article showing that a high dose of monthly vitamin D did not reduce the risk of death from any cause or from cancer and cardiovascular disease in older patients who in general did not have vitamin D deficiency.[14]

In 2022, the New England Journal of Medicine published results of a clinical trial showing that vitamin D supplements did not lower the risk of fractures in midlife and elderly patients who did not have low vitamin D levels, low bone mass or osteoporosis.[15]