Vitamin D

Overview

Vitamin D is a nutrient the body needs, along with calcium, to build bones and keep them healthy. The body can absorb calcium only if it has enough vitamin D. Calcium is a major part of bones.

Vitamin D also has many other uses in the body. It supports immune health and helps keep muscles and brain cells working.

Vitamin D isn't in many foods unless it's added. It's added to fortified milk and cereal. And it's in fish such as salmon, mackerel, and sardines. The body also makes vitamin D from direct sunlight on the skin.

How much vitamin D the body makes depends on many things. These include the time of day you're in the sun, what season it is, where you live, and the color of your skin. Depending on where you live and your lifestyle, you might get little to no vitamin D from the sun during winter. Although you need sunscreen to prevent skin cancer, using it also can lessen how much vitamin D your body makes.

Many older adults don't get enough direct sunlight. They also may have trouble taking in vitamin D. Other people who may not get enough vitamin D are breastfed babies, people with Black or brown skin, and people who have obesity or have had gastric bypass surgery. People with conditions that affect how the body absorbs fat, such as ulcerative colitis and Crohn's disease, also may not get enough vitamin D.

If you think you don't get enough vitamin D, talk with your healthcare professional. A simple blood test can check the levels of this vitamin in your blood.

Taking a vitamin D supplement or a multivitamin with vitamin D may 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 people ages 1 to 70 years, and 800 IU for people over 70 years.

What the research says

Research on vitamin D use for certain conditions shows:

• Cancer. Findings on whether vitamin D can help prevent cancer are mixed. More studies are needed to find out whether vitamin D supplements may lower the risk of certain cancers or the risk of dying from cancer.
• Cognitive health. Research shows that people with low levels of vitamin D in the blood are less able to think and learn, called cognitive decline. But more studies are needed to find out whether vitamin D supplements may help.
• Bone conditions passed through families, called inherited conditions. Vitamin D supplements can be used to help treat inherited conditions that happen when the body can't take in or use vitamin D. One such condition is familial hypophosphatemia.
• Multiple sclerosis. Research suggests that long-term use of vitamin D supplements may lower the risk of multiple sclerosis. More study is needed.
• Osteomalacia. Vitamin D supplements treat adults with extreme vitamin D deficiency that results in this softening of the bones.
• Osteoporosis. Studies suggest that people who get enough vitamin D and calcium in their diets can slow bone mineral loss. This helps prevent the bone-thinning condition osteoporosis and lower the number of bone fractures osteoporosis causes.
• Psoriasis. Vitamin D treats plaque-type psoriasis in some people. Vitamin D or a cream that has a form of vitamin D called calcipotriene can be used on the skin.
• Rickets. Not having enough vitamin D in the body can cause this rare condition that weakens bones in children. Taking a vitamin D supplement can prevent and treat the condition.

Our take

Generally safe

Without vitamin D, bones can become soft, thin and brittle. Not having enough vitamin D also is linked to the bone-thinning condition osteoporosis. People who don't get enough vitamin D from sunlight or diet may need vitamin D supplements.

Safety and side effects

Taken in typical doses, vitamin D is thought to be mainly safe.

But taking too much vitamin D in the form of supplements can be harmful and even deadly. Taking more than 4,000 IU a day of vitamin D might cause:

• Upset stomach and vomiting.
• Weight loss and not wanting to eat.
• Muscle weakness.
• Not being able to think clearly or quickly.
• Heart rhythm issues.
• Kidney stones and kidney damage.

Interactions

Possible interactions include:

• Aluminum. Taking vitamin D and phosphate binders that have aluminum might cause harmful levels of aluminum in people with kidney failure. Phosphate binders treat high blood levels of phosphate in people with longtime kidney disease.
• Anticonvulsants. The anticonvulsant medicines phenobarbital (Sezaby) and phenytoin (Dilantin, Phenytek) break down more vitamin D. This lessens how well the body can take in calcium.
• Atorvastatin (Lipitor). Taking vitamin D may affect the way the body uses this cholesterol medicine.
• Calcipotriene (Dovonex, Sorilux). Don't take vitamin D with this psoriasis medicine. Mixing the two might raise the risk of having too much calcium in the blood, called hypercalcemia.
• Cholestyramine (Prevalite, Locholest). Taking vitamin D with this cholesterol-lowering medicine can lower how much vitamin D the body takes in.
• Cytochrome P450 3A4 substrates, also called CYP3A4 substrates. Use vitamin D with care if you take a medicine affected by these enzymes. One such medicine is the cholesterol-lowering medicine lovastatin (Altoprev).
• Digoxin (Lanoxin). Don't take high doses of vitamin D with this heart medicine. High doses of vitamin D can cause too much calcium in the blood, called hypercalcemia. Hypercalcemia raises the risk of fatal heart conditions with digoxin.
• Diltiazem (Cardizem, Tiazac, others). Don't take high doses of vitamin D with this blood pressure medicine. High doses of vitamin D can cause too much calcium in the blood, called hypercalcemia. Hypercalcemia may keep the medicine from working as it should.
• Orlistat (Xenical, Alli). Taking this weight-loss medicine can lower how much vitamin D the body takes in.
• Thiazide diuretics. Taking these blood pressure medicines with vitamin D raises the risk of too much calcium in the blood, called hypercalcemia.
• Steroids. Taking steroid medicines such as prednisone can keep the body from taking in calcium and affect how the body uses vitamin D.
• Stimulant laxatives. Long-term use of high doses of stimulant laxatives can lessen how much vitamin D and calcium the body takes in.
• Verapamil (Verelan). Taking high doses of vitamin D with this blood pressure medicine can cause too much calcium in the blood, called hypercalcemia. High doses of vitamin D also might keep verapamil from working as well.