What is vitamin D and what is it used for?
Vitamin D is a nutrient necessary for good health. It helps the body absorb calcium, one of the main substances needed for strong bones. Together with calcium, vitamin D helps prevent osteoporosis, a disease that causes bones to become thinner and weaker and more prone to fractures. The body also needs vitamin D for other functions. Muscles need it for movement and nerves need it to transmit messages between the brain and other parts of the body. Vitamin D is essential for the immune system to fight off bacteria and viruses that attack it.
How much vitamin D do I need?
The amount of vitamin D a person needs each day will depend on their age. Below are the average recommended daily amounts in micrograms (mcg) and international units (IU):
| Stage of life | Recommended quantity |
|---|---|
| Babies up to 12 months | 10 mcg (400 IU) |
| Children from 1 to 13 years old | 15 mcg (600 IU) |
| Teenagers from 14 to 18 years old | 15 mcg (600 IU) |
| Adults 19 to 70 years old | 15 mcg (600 IU) |
| Adults over 71 years old | 20 mcg (800 IU) |
| Pregnant or breastfeeding women and adolescents | 15 mcg (600 IU) |
What foods contain vitamin D?
Very few foods contain vitamin D naturally. Foods fortified with vitamin D provide the majority of vitamin D in American diets. Read the product label to find out how much vitamin D a food or beverage contains.
- Nearly all of the U.S. milk supply is fortified with about 3 mcg (120 IU) of vitamin D per cup, as are many of the plant-based alternatives, such as soy milk, almond milk, and oat milk. However, foods made from milk, such as cheeses and ice cream, are typically not fortified.
- Additionally, many breakfast cereals and some brands of orange juice, yogurt, margarines and other products contain added vitamin D.
- Fatty fish, such as trout, salmon, tuna and mackerel, as well as fish liver oils, are among the best natural sources of vitamin D.
- Beef liver, egg yolks and cheese contain small amounts of vitamin D.
- Mushrooms provide some vitamin D. Some mushrooms are exposed to ultraviolet light to increase their vitamin D content.
Does sunlight provide vitamin D?
The body produces vitamin D when exposed skin is exposed to sunlight. Most people get at least some vitamin D this way. However, clouds, smog, older age, and dark skin reduce the amount of vitamin D produced by the skin. Likewise, skin exposed to sunlight through a window does not produce vitamin D.
Ultraviolet radiation from the sun can cause skin cancer, so it’s important to limit your exposure time. Although sunscreens limit vitamin D production, health experts recommend using those with a sun protection factor (SPF) of 15 or higher if you’re going to be in the sun for more than a few minutes.
What types of vitamin D dietary supplements can I get?
Vitamin D is found in multivitamin and multimineral supplements. It is also available in dietary supplements containing only vitamin D or vitamin D combined with a few other nutrients. The two forms of vitamin D available in supplements are D2 (ergocalciferol) and D3 (cholecalciferol). Both increase the concentration of vitamin D in the blood, although D3 may raise it more and for a longer time than D2. Because vitamin D is fat-soluble, it is best absorbed when taken with a meal or snack that contains some fat.
Do I get enough vitamin D?
Because our sources of vitamin D are food, sunshine, and dietary supplements, one way to tell if we’re getting enough vitamin D is a blood test that measures the concentration of this vitamin. In the blood, a form of vitamin D called 25-hydroxyvitamin D is measured in nanomoles per liter (nmol/L) or nanograms per milliliter (ng/mL). One nmol/L is equal to 0.4 ng/mL. For example, 50 nmol/L is equal to 20 ng/mL.
- Levels of 50 nmol/L (20 ng/mL) or higher are sufficient in most people to maintain bone health and overall health.
- Levels below 30 nmol/L (12 ng/mL) are too low and could weaken bones and harm health.
- Levels above 125 nmol/L (50 ng/mL) are too high and could cause health problems.
In the United States, most people have adequate levels of vitamin D in their blood. However, nearly one in four people have blood levels of vitamin D that are too low or insufficient for bone and overall health.
Some people have more difficulty than others getting enough vitamin D:
- Infants. Breast milk alone does not provide sufficient amounts of vitamin D. Infants should receive a supplement of 10 mcg (400 IU) of vitamin D per day.
- Older adults: With age, the skin’s ability to produce vitamin D when exposed to sunlight decreases.
- People who rarely expose their skin to the sun because they do not go outdoors or because they keep their body and head covered. Sunscreens also limit the amount of vitamin D produced by the skin.
- Dark-skinned people: The darker the skin, the less vitamin D it will produce when exposed to sunlight.
- People with disorders that limit fat absorption, such as Crohn’s disease, celiac disease, or ulcerative colitis. This is because ingested vitamin D is absorbed in the intestine along with fat. Therefore, if the body has trouble absorbing fat, it will also have trouble absorbing vitamin D.
- People who are obese or have had gastric bypass surgery. These people often need more vitamin D than others.
What happens if I don’t get enough vitamin D?
In children, vitamin D deficiency causes rickets, a disease in which bones become soft, weak, deformed and painful. In adolescents and adults, vitamin D deficiency causes osteomalacia, a disorder that causes bone pain and muscle weakness.
What are some of the health effects of vitamin D?
Scientists are studying vitamin D to better understand how it affects health. Here are some examples of the results of this research:
Bone health and osteoporosis
Long-term deficiency of vitamin D and calcium causes bones to become brittle and break more easily. This condition is called osteoporosis. Millions of older men and women have the condition or are at risk for it. Muscles are also important for bone health because they help maintain balance and prevent falls. Vitamin D deficiency can cause muscle weakness and pain.
Getting the recommended amounts of vitamin D and calcium from food (and supplements, if needed) helps maintain healthy bones and prevent osteoporosis. Vitamin D and calcium supplements slightly increase bone strength in older adults, although it is not clear whether they reduce the risk of falls or fractures.