Source = US National Library of Medicine

Effective for...

• Treating conditions that cause weak and painful bones (osteomalacia).
• Low levels of phosphate in the blood (familial hypophosphatemia).
• Low levels of phosphate in the blood due to a disease called Fanconi syndrome.
• Psoriasis (with a specialized prescription-only form of vitamin D).
• Low blood calcium levels because of a low parathyroid thyroid hormone levels.
• Helping prevent low calcium and bone loss (renal osteodystrophy) in people with kidney failure.
• Rickets.
• Vitamin D deficiency.

Likely effective for...

• Treating osteoporosis (weak bones). Taking a specific form of vitamin D called cholecalciferol (vitamin D3) along with calcium seems to help prevent bone loss and bone breaks.
• Preventing falls in older people. Researchers noticed that people who don’t have enough vitamin D tend to fall more often than other people. They found that taking a vitamin D supplement reduces the risk of falling by up to 22%. Higher doses of vitamin D are more effective than lower doses. One study found that taking 800 IU of vitamin D reduced the risk of falling, but lower doses didn’t.
  • Also, vitamin D, in combination with calcium, but not calcium alone, may prevent falls by decreasing body sway and blood pressure. This combination prevents more falls in women than men.
• Reducing bone loss in people taking drugs called corticosteroids.

Possibly effective for...

• Reducing the risk of multiple sclerosis (MS). Studies show taking vitamin D seems to reduce women’s risk of getting MS by up to 40%. Taking at least 400 IU per day, the amount typically found in a multivitamin supplement, seems to work the best.
• Preventing cancer. Some research shows that people who take a high-dose vitamin D supplement plus calcium might have a lower chance of developing cancer of any type.
• Weight loss. Women taking calcium plus vitamin D are more likely to lose weight and maintain their weight. But this benefit is mainly in women who didn’t get enough calcium before they started taking supplements.
• Flu. Some research in school aged children show that taking a vitamin D supplement during winter might reduce the chance of getting seasonal flu.
• Reducing the risk of rheumatoid arthritis in older women.
• Reducing bone loss in women with a condition called hyperparathyroidism.
• Preventing tooth loss in the elderly.

Possibly ineffective for...

• Breast cancer. Many studies have looked at whether vitamin D can help prevent breast cancer, but their results have not always agreed. The best evidence to date comes from a large study called the Women’s Health Initiative, which found that taking 400 IU of vitamin D and 1000 mg of calcium per day does not seem to lower the chance of getting breast cancer. The possibility remains that high doses of vitamin D might lower breast cancer risk in younger women. But the doses needed would be so high that they might not be safe.
• High blood pressure.
• Improving muscle strength in older adults.
• Preventing bone loss in people with kidney transplants.

Insufficient evidence to rate effectiveness for...

• Heart disease. Research suggests that people with low levels of vitamin D in their blood are much more likely to develop heart disease, including heart failure, than people with higher vitamin D levels. However, taking vitamin D does not seem to extend the life of people with heart failure.
• High cholesterol. People with lower vitamin D levels seem to be much more likely to have high cholesterol than people with higher vitamin D levels. Limited research shows that taking calcium plus vitamin D daily, in combination with a low-calorie diet, significantly raises “good (HDL) cholesterol” and lowers “bad (LDL) cholesterol” in overweight women. But taking calcium plus vitamin D alone, does not reduce LDL cholesterol levels.
• Gum disease. Higher blood levels of vitamin D seem to be linked with a reduced risk of gum disease in people 50 years of age or older. But, this doesn’t seem to be true for adults younger than 50.
• Diabetes. People with lower vitamin D levels are significantly more likely to have type 2 diabetes compared to people with higher vitamin D levels. But, there is no reliable evidence that taking vitamin D supplements can treat or prevent type 2 diabetes.
• Premenstrual syndrome (PMS). There is some evidence that getting more vitamin D from the diet might help to prevent PMS or reduce symptoms. Taking vitamin D supplements might help reduce symptoms but doesn't seem to help prevent PMS.
• A blood cell disease called myelodysplastic syndrome.
• A muscle disease called proximal myopathy.
• Colorectal cancer.
• Warts.
• Bronchitis.
• Asthma.
• Breathing disorders.
• Metabolic syndrome.
• Muscle pain caused by medications called "statins."
• Vaginal atrophy.
• Other conditions.
  • More evidence is needed to rate vitamin D for these uses.

How does it work?

Vitamin D is required for the regulation of the minerals calcium and phosphorus found in the body. It also plays an important role in maintaining proper bone structure.

Sun exposure is an easy, reliable way for most people to get vitamin D. Exposure of the hands, face, arms, and legs to sunlight two to three times a week for about one-fourth of the time it would take to develop a mild sunburn will cause the skin to produce enough vitamin D. The necessary exposure time varies with age, skin type, season, time of day, etc.

It’s amazing how quickly adequate levels of vitamin D can be restored by sunlight. Just 6 days of casual sunlight exposure without sunscreen can make up for 49 days of no sunlight exposure. Body fat acts like a kind of storage battery for vitamin D. During periods of sunlight, vitamin D is stored in fatty fat and then released when sunlight is gone.

Nevertheless, vitamin D deficiency is more common than you might expect. People who don’t get enough sun, especially people living in Canada and the northern half of the US, are especially at risk. Vitamin D deficiency also occurs even in sunny climates, possibly because people are staying indoors more, covering up when outside, or using sunscreens consistently these days to reduce skin cancer risk.

Older people are also at risk for vitamin D deficiency. They are less likely to spend time in the sun, have fewer “receptors” in their skin that convert sunlight to vitamin D, may not get vitamin D in their diet, may have trouble absorbing vitamin D even if they do get it in their diet, and may have more trouble converting dietary vitamin D to a useful form due to aging kidneys. In fact, the risk for vitamin D deficiency in people over 65 years of age is very high. Surprisingly, as many as 40% of older people even in sunny climates such as South Florida don’t have enough vitamin D in their systems.

Vitamin D supplements may be necessary for older people, people living in northern latitudes, and for dark-skinned people who need extra time in the sun, but don’t get it.

Are there safety concerns?

Vitamin D is LIKELY SAFE when taken by mouth in recommended amounts. Most people do not commonly experience side effects with vitamin D, unless too much is taken. Some side effects of taking too much vitamin D include weakness, fatigue, sleepiness, headache, loss of appetite, dry mouth, metallic taste, nausea, vomiting, and others.

Taking vitamin D for long periods of time in doses higher than 50 mcg (2000 units) per day is POSSIBLY UNSAFE and may cause excessively high levels of calcium in the blood. However, much higher doses are often needed for the short-term treatment of vitamin D deficiency. This type of treatment should be done under the supervision of a healthcare provider.

Special precautions & warnings:

• Pregnancy and breast-feeding:
  • Vitamin D is LIKELY SAFE during pregnancy and breast-feeding when used in daily amounts below 50 mcg (2000 units). Do not use higher doses. Using higher doses might cause serious harm to the infant.
• Kidney disease:
  • Vitamin D may increase calcium levels and increase the risk of “hardening of the arteries” in people with serious kidney disease. This must be balanced with the need to prevent renal osteodystrophy, a bone disease that occurs when the kidneys fail to maintain the proper levels of calcium and phosphorus in the blood. Calcium levels should be monitored carefully in people with kidney disease.
  • High levels of calcium in the blood: Taking vitamin D could make this condition worse.
• Hardening of the arteries” (atherosclerosis): Taking vitamin D could make this condition worse.
• Sarcoidosis: Vitamin D may increase calcium levels in people with sarcoidosis. This could lead to kidney stones and other problems. Use vitamin D cautiously.
• Histoplasmosis: Vitamin D may increase calcium levels in people with histoplasmosis. This could lead to kidney stones and other problems. Use vitamin D cautiously.
• Over-active parathyroid gland (hyperparathyroidism): Vitamin D may increase calcium levels in people with hyperparathyroidism. Use vitamin D cautiously.
• Lymphoma: Vitamin D may increase calcium levels in people with lymphoma. This could lead to kidney stones and other problems. Use vitamin D cautiously.

Are there interactions with medications?

Moderate : Be cautious with this combination.

• Aluminum
  • Aluminum is found in most antacids. Vitamin D can increase how much aluminum the body absorbs. This interaction might be a problem for people with kidney disease. Take vitamin D two hours before, or four hours after antacids.
• Atorvastatin (Lipitor)
  • Vitamin D might decrease the amount of atorvastatin (Lipitor) that enters the body. This might decrease how well atorvastatin (Lipitor) works.
• Calcipotriene (Dovonex)
  • Calcipotriene is a drug that is similar to vitamin D. Taking vitamin D along with calcipotriene (Dovonex) might increase the effects and side effects of calcipotriene (Dovonex). Avoid taking vitamin D supplements if you are taking calcipotriene (Dovonex).
• Digoxin (Lanoxin)
  • Vitamin D helps your body absorb calcium. Calcium can affect the heart. Digoxin (Lanoxin) is used to help your heart beat stronger. Taking vitamin D along with digoxin (Lanoxin) might increase the effects of digoxin (Lanoxin) and lead to an irregular heartbeat. If you are taking digoxin (Lanoxin), talk to your doctor before taking vitamin D supplements.
• Diltiazem (Cardizem, Dilacor, Tiazac)
  • Vitamin D helps your body absorb calcium. Calcium can affect your heart. Diltiazem (Cardizem, Dilacor, Tiazac) can also affect your heart. Taking large amounts of vitamin D along with diltiazem (Cardizem, Dilacor, Tiazac) might decrease the effectiveness of diltiazem.
• Medications changed by the liver (Cytochrome P450 3A4 (CYP 3A4) substrates)
  • Some medications are changed and broken down by the liver. Vitamin D may increase how quickly the liver breaks down some medications. Taking vitamin D along with some medications may decrease the effectiveness of some medications. Before taking vitamin D, talk to your health care provider if you are taking any medications that are changed by the liver.
  • Some of these medications changed by the liver include lovastatin (Mevacor), clarithromycin (Biaxin), cyclosporine (Neoral, Sandimmune), diltiazem (Cardizem), estrogens, indinavir (Crixivan), triazolam (Halcion), and others.
• Verapamil (Calan, Covera, Isoptin, Verelan)
  • Vitamin D helps your body absorb calcium. Calcium can affect the heart. Verapamil (Calan, Covera, Isoptin, Verelan) can also affect the heart. Do not take large amounts of vitamin D if you are taking verapamil (Calan, Covera, Isoptin, Verelan).
• Water pills (Thiazide diuretics)
  • Vitamin D helps your body absorb calcium. Some "water pills" increase the amount of calcium in the body. Taking large amounts of vitamin D along with some "water pills" might cause to be too much calcium in the body. This could cause serious side effects including kidney problems.
  • Some of these "water pills" include chlorothiazide (Diuril), hydrochlorothiazide (HydroDIURIL, Esidrix), indapamide (Lozol), metolazone (Zaroxolyn), and chlorthalidone (Hygroton).

Minor: Be watchful with this combination.

• Cimetidine (Tagamet)
  • The body changes vitamin D into a form that it can use. Cimetidine (Tagamet) might decrease how well the body changes vitamin D. This might decrease how well vitamin D works. But this interaction probably isn't important for most people.
• Heparin
  • Heparin slows blood clotting and can increase the risk of breaking a bone when used for a long period of time. People taking these medications should eat a diet rich in calcium and vitamin D.
• Low molecular weight heparins (LMWHs)
  • Some medications called low molecular weight heparins can increase the risk of breaking a bone when used for a long periods of time. People taking these medications should eat a diet rich in calcium and vitamin D.
  • These drugs include enoxaparin (Lovenox), dalteparin (Fragmin), and tinzaparin (Innohep).

Are there interactions with herbs and supplements?

• Magnesium
  • Taking vitamin D can raise the level of magnesium in people who have low magnesium and low vitamin D levels. In people with normal magnesium levels, this doesn't seem to happen.

There are no known interactions with foods.

The following doses have been studied in scientific research:

BY MOUTH:

• For preventing osteoporosis and fractures: 400-1000 IU per day has been used for older adults. Some experts recommended higher doses of 1000-2000 IU daily.
• For preventing falls: 800-1000 IU/day has been used in combination with calcium 1000-1200 mg/day.
• For preventing multiple sclerosis (MS): long-term consumption of at least 400 IU per day, mainly in the form of a multivitamin supplement, has been used.
• For preventing all cancer types: calcium 1400-1500 mg/day plus vitamin D3 (cholecalciferol) 1100 IU/day in postmenopausal women has been used.
• For muscle pain caused by medications called "statins": vitamin D2 (ergocalciferol) or vitamin D3 (cholecalciferol) 50,000 units once a week or 400 IU daily.
• For preventing the flu: vitamin D (cholecalciferol) 1200 IU daily.
  • Most vitamin supplements contain only 400 IU (10 mcg) vitamin D.
  • The Institute of Medicine publishes an Adequate Intake (AI) recommendation which is an estimate of the amount of vitamin D that appears to maintain normal functioning. The current daily AI of vitamin D to prevent rickets in healthy children and bone pain (osteomalacia) in adults is based on age. Birth through 50 years of age, 200 IU (5 mcg); Adults ages 51 to 70, 400 IU (10 mcg); Adults greater than 70 years of age, 600 IU (15 mcg) daily. The upper intake levels (UL) for vitamin D are 1000 IU (25 mcg) for infants 0 to 12 months and 2000 IU (50 mcg) for everyone over one year of age.

Some organizations are recommending higher amounts.

• In 2008, the American Academy of Pediatrics increased the recommended minimum daily intake of vitamin D to 400 IU daily for all infants and children, including adolescents. Parents should not use vitamin D liquids dosed as 400 IU/drop. Giving one dropperful or mL by mistake can deliver 10,000 IU/day. The US Food and Drug Administration (FDA) will force companies to provide no more than 400 IU per dropperful in the future.
• The National Osteoporosis Foundation recommends vitamin D 400 IU to 800 IU daily for adults under age 50, and 800 IU to 1000 IU daily for older adults.
• The North American Menopause Society recommends 700 IU to 800 IU daily for women at risk of deficiency due to low sun (e.g., homebound, northern latitude) exposure.
• Guidelines from the Osteoporosis Society of Canada recommend vitamin D 400 IU per day for people up to age 50, and 800 IU per day for people over 50.
• Osteoporosis Canada now recommends 400-1000 IU daily for adults under the age of 50 years and 800-2000 IU daily for adults over the age of 50 years.
• The Canadian Cancer Society recommends 1000 IU/day during the fall and winter for adults in Canada. For those with a higher risk of having low vitamin D levels, this dose should be taken year round. This includes people who have dark skin, usually wear clothing that covers most of their skin, and people who are older or who don't go outside often.
• Many experts now recommend using vitamin D supplements containing cholecalciferol in order to meet these intake levels. This seems to be more potent than another form of vitamin D called ergocalciferol.

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See also Vitamin D Life

• Medline rates vitamin D - A or B strength of evidence for 10 diseases - July 2010
• Vitamin D Recommendations IU and ng
• All items in category Drug interactions with Vitamin D 38 items as of Oct 2011
• Allergic reaction to vitamin D is rare Blog post at Vitamin D Life - Feb 2012