Vitamin D is necessary for building and maintaining healthy bones. That's because calcium, the primary component of bone, can only be absorbed by your body when vitamin D is present. Your body makes vitamin D when direct sunlight converts a chemical in your skin into an active form of the vitamin (calciferol).
Vitamin D isn't found in many foods, but you can get it from fortified milk, fortified cereal, and fatty fish such as salmon, mackerel and sardines.
The amount of vitamin D your skin makes depends on many factors, including the time of day, season, latitude and your skin pigmentation. Depending on where you live and your lifestyle, vitamin D production might decrease or be completely absent during the winter months. Sunscreen, while important, also can decrease vitamin D production.
Many older adults don't get regular exposure to sunlight and have trouble absorbing vitamin D, so taking a multivitamin with vitamin D will likely help improve bone health. The recommended daily amount of vitamin D is 400 international units (IU) for children up to age 12 months, 600 IU for ages 1 to 70 years, and 800 IU for people over 70 years.
Research on vitamin D use for specific conditions shows:
- Cancer. Research suggests that vitamin D, especially when taken with calcium, might help prevent certain cancers.
- Cognitive health. Early research suggests that vitamin D might play a role in cognitive health. In one small study of adults age 60 years and older being treated for dementia, researchers found that taking a vitamin D supplement helped improve cognitive function.
- Inherited disorders. Vitamin D supplements can be used to help treat inherited disorders resulting from an inability to absorb or process vitamin D, such as familial hypophosphatemia.
- Multiple sclerosis. Research suggests that long-term vitamin D supplementation reduces the risk of multiple sclerosis.
- Osteomalacia. Vitamin D supplements are used to treat adults with severe vitamin D deficiency, resulting in loss of bone mineral content, bone pain, muscle weakness and soft bones (osteomalacia).
- Osteoporosis. Studies suggest that people who get enough vitamin D and calcium in their diets can slow bone mineral loss, help prevent osteoporosis and reduce bone fractures.
- Psoriasis. Applying vitamin D or a topical preparation that contains a vitamin D compound called calcipotriene to the skin can treat plaque-type psoriasis in some people.
- Rickets. This rare condition develops in children with vitamin D deficiency. Supplementing with vitamin D can prevent and treat the problem.
Without vitamin D your bones can become soft, thin and brittle. Insufficient vitamin D is also connected to osteoporosis and some types of cancer. If you don't get enough vitamin D through sunlight or dietary sources, you might need vitamin D supplements.
Safety and side effects
Taken in appropriate doses, vitamin D is generally considered safe.
However, taking too much vitamin D can be harmful. Children age 9 years and older, adults, and pregnant and breast-feeding women who take more than 4,000 IU a day of vitamin D might experience:
- Poor appetite
- Weight loss
- Heart rhythm problems
- Kidney damage
Possible interactions include:
- Aluminum. Taking vitamin D and aluminum-containing phosphate binders long term might cause harmful levels of aluminum in people with kidney failure.
- Anticonvulsants. The anticonvulsants phenobarbital and phenytoin (Dilantin, Phenytek) increase the breakdown of vitamin D and reduce calcium absorption.
- Atorvastatin (Lipitor). Taking vitamin D might affect the way your body processes this cholesterol drug.
- Calcipotriene (Dovonex). Don't take vitamin D with this psoriasis drug. The combination might increase the risk of too much calcium in the blood (hypercalcemia).
- Cholestyramine (Prevalite). Taking this weight-loss drug can reduce your absorption of vitamin D.
- Cytochrome P450 3A4 (CYP3A4) substrates. Use vitamin D cautiously if you're taking drugs processed by these enzymes.
- Digoxin (Lanoxin). Avoid taking high doses of vitamin D with this heart medication. High doses of vitamin D can cause hypercalcemia, which increases the risk of fatal heart problems with digoxin.
- Diltiazem (Cardizem, Tiazac). Avoid taking high doses of vitamin D with this blood pressure drug. High doses of vitamin D can cause hypercalcemia, which might reduce the drug's effectiveness.
- Orlistat (Xenical, Alli). Taking this weight-loss drug can reduce your absorption of vitamin D.
- Thiazide diuretics. These blood pressure drugs might decrease urinary calcium excretion. This could lead to hypercalcemia if you are taking vitamin D.
- Steroids. Taking steroid mediations such as prednisone can reduce calcium absorption and impair your body's processing of vitamin D.
- Stimulant laxatives. Long-term use of high doses of stimulant laxatives can reduce vitamin D and calcium absorption.
- Verapamil (Verelan, Calan). Avoid taking high doses of vitamin D with this blood pressure drug. High doses of vitamin D can cause hypercalcemia, which might reduce the drug's effectiveness.