Vitamin D

Definition

Vitamin D is a fat-soluble vitamin. Fat-soluble vitamins are stored in the body's fatty tissue.

Function

Vitamin D helps the body absorb calcium. Calcium and phosphate are two minerals that you must have for normal bone formation.

In childhood, your body uses these minerals to produce bones. If you do not get enough calcium, or if your body does not absorb enough calcium from your diet, bone production and bone tissues may suffer.

Vitamin D deficiency can lead to osteoporosis in adults or rickets in children.

Food Sources

The body makes vitamin D when the skin is directly exposed to the sun. That is why it is often called the "sunshine" vitamin. Most people meet at least some of their vitamin D needs this way.

Very few foods naturally contain vitamin D. As a result, many foods are fortified with vitamin D. Fortified means that vitamins have been added to the food.

Fatty fish (such as tuna, salmon, and mackerel) are among the best sources of vitamin D.

Beef liver, cheese, and egg yolks provide small amounts.

Mushrooms provide some vitamin D. Some mushrooms you buy in the store have higher vitamin D content because they have been exposed to ultraviolet light.

Most milk in the United States is fortified with 400 IU vitamin D per quart. Most of the time, foods made from milk, such as cheese and ice cream, are not fortified.

Vitamin D is added to many breakfast cereals. It is also added to some brands of soy beverages, orange juice, yogurt, and margarine. Check the nutrition fact panel on the food label.

SUPPLEMENTS

It can be hard to get enough vitamin D from food sources alone. As a result, some people may need to take a vitamin D supplement. Vitamin D found in supplements and fortified foods comes in two different forms:

Follow a diet that provides the proper amount of calcium and vitamin D. Your provider may recommend higher doses of vitamin D if you have risk factors for osteoporosis or a low level of this vitamin.

Side Effects

Too much vitamin D can make the intestines absorb too much calcium. This may cause high levels of calcium in the blood. High blood calcium can lead to:

Recommendations

Some experts have suggested that a few minutes of sunlight directly on the skin of your face, arms, back, or legs (without sunscreen) every day can produce the body's requirement of vitamin D. However, the amount of vitamin D produced by sunlight exposure can vary greatly from person to person.

The best measure of your vitamin D status is to look at blood levels of a form known as 25-hydroxyvitamin D. Blood levels are described either as nanograms per milliliter (ng/mL) or nanomoles per liter (nmol/L), where 0.4 ng/mL = 1 nmol/L.

Levels below 30 nmol/L (12 ng/mL) are too low for bone or overall health, and levels above 125 nmol/L (50 ng/mL) are probably too high. Levels of 50 nmol/L or above (20 ng/mL or above) are enough for most people.

The Recommended Dietary Allowance (RDA) for vitamins reflects how much of each vitamin most people should get on a daily basis.

Infants (adequate intake of vitamin D)

Children

Older children and adults

The National Osteoporosis Foundation (NOF) recommends a higher dose for people age 50 and older, 800 to 1,000 IU of vitamin D daily. Ask your health care provider which amount is best for you.

Vitamin D toxicity almost always occurs from using too many supplements. The safe upper limit for vitamin D is:

One microgram of cholecalciferol (D3) is the same as 40 IU of vitamin D.


Review Date: 2/2/2019
Reviewed By: Emily Wax, RD, CNSC, University of Virginia Health System, Charlottesville, VA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

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