Vitamin D is a nutrient the body needs to build strong bones and keep them healthy. That's why the body can only absorb calcium, the main component of bone, when vitamin D is present. Vitamin D also regulates many other cellular functions in the body. Its anti-inflammatory, antioxidant, and neuroprotective properties contribute to a healthy immune system, muscle function, and brain cell activity.
Vitamin D is not found naturally in many foods, but you can get it from fortified milk, fortified cereals, and oily fish, such as salmon, sardines, and mackerel. The body also makes vitamin D when direct sunlight converts a chemical in the skin to the active form of the vitamin (calciferol).
The amount of vitamin D produced by the skin depends on many factors, including the time of day, season, latitude, and skin pigmentation. Depending on where you live and what your lifestyle is, vitamin D production can drop to zero during the winter months. Although important for preventing skin cancer, sunscreens can also decrease vitamin D production.
Many older adults do not get regular sunlight exposure and have trouble absorbing vitamin D. If your doctor suspects that you are deficient in vitamin D, he or she can check for it with a simple blood test.
Taking a multivitamin with vitamin D can help improve bone health. The recommended daily allowance for vitamin D is 400 international units (IU) for children up to 12 months of age, 600 IU for people ages 1 to 70, and 800 for people 70 and older.
Evidence
In research on the use of vitamin D for specific conditions, it can be observed:
Cancer. Findings on the benefits of vitamin D for cancer prevention are mixed. More studies are needed to determine if vitamin D supplementation can reduce the risk of certain types of cancer.
Cognitive health. Research shows that low levels of vitamin D in the blood are associated with cognitive decline. However, more studies are needed to determine the benefits of vitamin D supplementation for cognitive health.
Inherited bone disorders. Vitamin D supplements can be used to treat inherited disorders that result from an inability to absorb and process vitamin D, such as hypophosphatemia.
Multiple sclerosis. Some 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, which causes loss of bone mineral content, bone pain, muscle weakness, and 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 fractures. Consult your doctor if you need a calcium and vitamin D supplement to prevent or treat osteoporosis.
Psoriasis. Applying a vitamin D preparation or topical containing a vitamin D compound called calcipotriol to the skin can help treat plaque psoriasis in some people.
Rickets. This rare condition develops in children with vitamin D deficiency. Taking a vitamin D supplement can prevent and treat the problem.
Our recommendation
It's generally safe
Without vitamin D, bones can become soft, thin, and brittle. An insufficient amount of vitamin D is also associated with osteoporosis. If you don't get enough vitamin D from the sun or food sources, you may need to take vitamin D supplements.
Safety and side effects
Taken in adequate doses, vitamin D is generally considered safe.
However, taking too much vitamin D in the form of supplements can be harmful. Children older than 9 years, adults, and pregnant or lactating women who take more than 4,000 IU per day of vitamin D may experience the following:
nausea and vomiting
poor appetite and weight loss
Constipation
Weakness
confusion and disorientation
heart rhythm problems
Kidney stones and kidney damage
interactions
Potential interactions include:
Aluminum. Taking vitamin D and aluminum phosphate binders, which can be used to treat high serum phosphate levels in people with chronic kidney disease, can cause harmful long-term aluminum levels.
Anticonvulsants. The anticonvulsants phenobarbital and phenytoin (Dilantin, Phenytek) increase the breakdown of vitamin D and reduce calcium absorption.
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