Vitamin D

Definition

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

Alternative Names

Cholecalciferol; Vitamin D3; Ergocalciferol; Vitamin D2

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:

• D2 (ergocalciferol)
• D3 (cholecalciferol)

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:

• Calcium deposits in soft tissues such as the heart and lungs
• Confusion and disorientation
• Damage to the kidneys
• Kidney stones
• Nausea, vomiting, constipation, poor appetite, weakness, and weight loss

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.

• People who do not live in sunny places may not make enough vitamin D within a limited time in the sun. Cloudy days, shade, and having dark-colored skin also cut down on the amount of vitamin D the skin makes.
• Because exposure to sunlight is a risk for skin cancer, exposure for more than a few minutes without sunscreen is not recommended.

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.

• The RDA for vitamins may be used as goals for each person.
• How much of each vitamin you need depends on your age and sex. Other factors, such as pregnancy and your health, are also important.

Infants (adequate intake of vitamin D)

• 0 to 6 months: 400 IU (10 micrograms [mcg] per day)
• 7 to 12 months: 400 IU (10 mcg/day)

Children

• 1 to 3 years: 600 IU (15 mcg/day)
• 4 to 8 years: 600 IU (15 mcg/day)

Older children and adults

• 9 to 70 years: 600 IU (15 mcg/day)
• Adults over 70 years: 800 IU (20 mcg/day)
• Pregnancy and breastfeeding: 600 IU (15 mcg/day)

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:

• 1,000 to 1,500 IU/day for infants (25 to 38 mcg/day)
• 2,500 to 3,000 IU/day for children 1 to 8 years; ages 1 to 3: 63 mcg/day; ages 4 to 8: 75 mcg/day
• 4,000 IU/day for children 9 years and older, adults, and pregnant and breastfeeding teens and women (100 mcg/day)

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

Images

References

Mason JB, SL Booth. Vitamins, trace minerals, and other micronutrients. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 26th ed. Philadelphia, PA: Elsevier; 2020:chap 205.

National Osteoporosis Foundation website. Clinician's guide to prevention and treatment of osteoporosis. cdn.nof.org/wp-content/uploads/2016/01/995.pdf.  Accessed November 9, 2020.

Salwen MJ. Vitamins and trace elements. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 23rd ed. St Louis, MO: Elsevier; 2017:chap 26.