When the sun shines on a person’s(mammalian) skin, it triggers a chemical reaction that produces the vitamin, according to the National Library of Medicine. Very few foods naturally contain vitamin D, but it can be found in foods that come from animals, including meat and dairy.
Mushrooms are the only produce that naturally contains vitamin D.
Some mushrooms you buy in the store have higher vitamin D content because they have been exposed to ultraviolet light.
Vitamin D is a fat-soluble vitamin. Fat-soluble vitamins are stored in the body’s fatty tissue.
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.
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.
It can be very 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)
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
Ten to 15 minutes of sunshine 3 times weekly is enough to produce the body’s requirement of vitamin D. The sun needs to shine on the skin of your face, arms, back, or legs (without sunscreen). Because exposure to sunlight is a risk for skin cancer, you should use sunscreen after a few minutes in the sun.
People who do not live in sunny places may not make enough vitamin D. Skin that is exposed to sunshine indoors through a window will not produce vitamin D. Cloudy days, shade, and having dark-colored skin also cut down on the amount of vitamin D the skin makes.
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.
Vitamin D toxicity almost always occurs from using too many supplements.