Vitamin D is essential for regulating the minerals calcium and phosphorus in the body to maintain proper and healthy bone structure. A lack of vitamin D increases the risk of certain diseases.

1. What does vitamin D do?

Vitamin D is one of the most important vitamins for the body. When the body is deficient in vitamin D, it can lead to many health consequences, increasing the risk of certain diseases such as type 1 diabetes, muscle and bone pain, and more seriously, can lead to breast, colon, prostate, ovarian, esophageal and lymphatic cancers.

Vitamin D is essential for building and maintaining strong bones, because calcium is the main component of bones and can only be absorbed by the body when there is vitamin D. Your body creates vitamin D when sunlight shines directly on the skin and converts the chemical in the skin into the active form of the vitamin (calciferol).

Vitamin D is not found in many foods, but you can get it from vitamin D-fortified milk, fortified cereals, 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 skin pigmentation. Depending on where you live and your lifestyle, vitamin D production may decrease or disappear completely during the winter months. Sunscreen can also reduce vitamin D production.

Older people are also at risk for vitamin D deficiency because they spend less time in the sun and have fewer “receptors” in their skin to convert sunlight into vitamin D. Low dietary vitamin D, difficulty absorbing vitamin D even if they eat enough, and kidney problems.

Vitamin D supplementation may be necessary for older adults, people living in northern latitudes, and darker-skinned people who need extra time in the sun, but don’t take vitamin D supplements on your own. Talk to your doctor before deciding whether vitamin D supplementation is right for you.

2. Recommended Vitamin D Doses

The Food and Nutrition Board of the National Academy of Sciences has established a Recommended Dietary Allowance (RDA) for vitamin D that represents an adequate daily intake for the maintenance of bone health and normal calcium metabolism in healthy individuals. The RDA for vitamin D uses international units (IU) and micrograms (mcg); the biological activity of 40 IU is equivalent to 1 mcg. Although sunlight may be the main source of vitamin D for some people, the RDA for vitamin D is established based on minimal exposure to sunlight.

3. How long to take vitamin D?

Adults by mouth

• For people with vitamin D deficiency: 50,000 IU per week for 6 – 12 weeks.
• To prevent osteoporosis: 400-1000 IU/day of vitamin D3 (also known as cholecalciferol) in older adults. It is usually taken with 500-1200 mg of calcium per day. Some experts recommend higher doses of 1000-2000 IU per day combined with calcitriol 0.43-1.0 mcg/day for up to 36 months.
• To prevent bone loss due to corticosteroid use: 0.25-1.0 mcg/day of vitamin D in a form called calcitriol or alfacalcidol for 6-36 months.
• For heart failure: 800 IU/day of vitamin D as cholecalciferol alone or with 1000 mg/day of calcium for 3 years.
• Or 400 IU/day of vitamin D as cholecalciferol with 1000 mg/day of calcium in postmenopausal women.
• For bone loss due to hyperparathyroidism: 800 IU/day of vitamin D as cholecalciferol for 3 months.
• Multiple sclerosis: 400 IU/day of vitamin D.
• To prevent respiratory tract infections: 300-4000 IU of vitamin D as cholecalciferol for 7 weeks to 13 months.
• To prevent tooth loss in the elderly: 700 IU/day of vitamin D as cholecalciferol combined with 500 mg/day of calcium for 3 years.

How long should infants take vitamin D?

The American Academy of Pediatrics recommends the following:

• If you are breastfeeding, give your baby 400 IU of vitamin D daily, starting soon after birth. Continue giving your baby vitamin D until your baby is weaned from breastfeeding and continues to drink about 1 quart of vitamin D-fortified formula per day or is drinking whole cow’s milk after 12 months of age.
• If your baby is consuming less than about 1 quart of vitamin D-fortified formula per day, give your baby 400 IU of liquid vitamin D per day, starting in the first few days after birth. Continue giving your baby vitamin D until your baby is consuming at least 1 quart of vitamin D-fortified formula per day.

4. Side effects of vitamin D

When used in appropriate doses, vitamin D is safe for humans. However, too much vitamin D can cause unwanted effects. Children 9 years of age and older, adults, and pregnant and lactating women who take more than 4,000 IU of vitamin D per day may experience the following:

• Nausea
• Vomiting
• Poor appetite
• Constipation
• Weakness
• Weight loss

Vitamin D may cause unwanted weight loss

• Confusion
• Disorientation
• Heart rhythm problems
• Kidney damage

Drug interactions

Interactions may include:

• Aluminum: Taking vitamin D and phosphate binders that contain aluminum, if taken for a long time, can increase harmful aluminum levels in people with kidney failure.
• Anticonvulsants: Anticonvulsants such as phenobarbital and phenytoin (Dilantin, Phenytek) increase the breakdown of vitamin D and reduce calcium absorption.
• Atorvastatin (Lipitor): Taking vitamin D may affect the effectiveness of this cholesterol medication.
• Calcipotriene (Dovonex): Do not take vitamin D with this psoriasis medication because taking it together can increase blood calcium levels.
• Cholestyramine (Prevalite): Taking this weight loss drug can decrease the absorption of vitamin D.
• Digoxin (Lanoxin): Avoid taking high doses of vitamin D with this heart medication because high doses of vitamin D can cause hypercalcemia, which increases the risk of fatal heart problems from digoxin.
• Diltiazem (Cardizem, Tiazac): Avoid taking high doses of vitamin D with this blood pressure medication because high doses of vitamin D can cause hypercalcemia, which reduces the effectiveness of the medication.
• Orlistat (Xenical, Alli) reduces the absorption of vitamin D.
• Thiazide diuretics used to treat high blood pressure can decrease the excretion of calcium in the urine, leading to increased blood calcium levels if you are taking vitamin D.
• Steroids: Taking steroid medications such as prednisone can decrease the absorption of calcium and decrease the body’s ability to process vitamin D.
• Verapamil (Verelan, Calan): Avoid taking high doses of vitamin D with this medication because high doses of vitamin D can cause hypercalcemia and reduce the effectiveness of the medication.