What is Vitamin D?

Why is vitamin D important?

Vitamin D has significant effects on human health and plays an important role in bone health. Vitamin D is involved in many cellular functions in the human body. Some research suggests that vitamin D may impact the development or progression of other diseases including diabetes, heart disease, and cancer. Because vitamin D has effects on the immune system, some researchers have investigated whether vitamin D supplementation is effective in preventing infections, including COVID-19. However, there is currently no definitive proof that vitamin D supplementation is an effective method of preventing infections.    

Is vitamin D from the sun?

Vitamin D3, the primary form of vitamin D found in humans, is produced by the skin after exposure to ultraviolet-B (UV-B) radiation, including sunlight. Skin synthesis of vitamin D3 is responsible for up to 90% of the vitamin D found in the human body. Another type of vitamin D, vitamin D2, is obtained from plants, including mushrooms and other fungi.

Is vitamin D the same as D3?

There are two forms of vitamin D: vitamin D2 and vitamin D3. Vitamin D2 (ergocalciferol) is derived from plants, and vitamin D3 (cholecalciferol) is synthesized by the skin. Dietary supplements may contain vitamin D2, vitamin D3, or both. Many studies suggest that vitamin D3 supplements are more effective than vitamin D2 supplements in raising vitamin D levels in humans.

What foods have vitamin D?

There are very few foods that are rich in vitamin D. Cod liver oil and certain types of fish (including salmon and trout) are good sources of vitamin D. Milk and cereal products are often fortified with vitamin D. Some varieties of mushrooms contain significant amounts of vitamin D, and mushroom powder is approved by the United States Food and Drug Administration (FDA) as an additive to increase the vitamin D content of foods.

Can you get vitamin D through windows?

UV-B light, which promotes vitamin D synthesis within human skin, cannot penetrate through window glass, automobile windshields, or other forms of glass. Because of this, people who work indoors or spend a significant amount of time in their vehicles may be at risk for vitamin D deficiency.

What are the causes of vitamin D deficiency?

Since sunlight is required for our bodies to make vitamin D naturally, individuals who have low or inadequate exposures to sunlight can easily develop vitamin D deficiency. The time of year, amount of daily sun exposure, skin tone, and geographical location can all impact the amount of vitamin D produced by an individual. Since many people work indoors, do not go outside to get exposure to sunlight on a regular basis, and wear heavy clothes that prevent sunlight from penetrating the skin, vitamin D deficiency is relatively common. In addition, because reduced vitamin D skin synthesis occurs in older individuals, people with gastrointestinal or kidney diseases, and pregnant women, these populations are also at risk for vitamin D deficiencies.

What are symptoms of vitamin D deficiency?

One of the most recognizable manifestations of vitamin D deficiency is the childhood disease called rickets. In patients with rickets, the deficiency of Vitamin D impacts calcium absorption and causes bone diseases, scoliosis, and growth deficiencies. Other symptoms of vitamin D deficiency can include muscle weakness and fatigue. Vitamin D deficiency is also associated with some types of hair loss, including alopecia areata.

Does vitamin D supplementation work?

The use of vitamin D supplements may be beneficial for people who are diagnosed with vitamin D deficiency. For people who do not have vitamin D deficiency, the role of vitamin D supplements is less clear, and use of these supplements may not have significant health benefits in these individuals.

Which vitamin D supplement is best?

The recommended dose of vitamin D for a particular person depends on multiple factors, including the individual’s other medical conditions, skin tone, and exposure to sunlight. Some authorities recommend that healthy adults take 800-2000 IU of vitamin D supplements daily during the winter months (when most people have less sun exposure) for prevention of vitamin D deficiency. For individuals diagnosed with vitamin D deficiency, higher doses of vitamin D supplements may be required.

What do I do if I take too much vitamin D?

Vitamin D can cause toxicity when taken in excess. For questions about unwanted or unexpected events related to the use of vitamin D, contact poison control for expert advice. There are two ways to contact poison control: go online to www.poison.org or call 1-800-222-1222. Both options are free to the public, confidential, and available 24 hours a day.

Kelly Johnson-Arbor, MD
Medical Toxicologist

For media inquiries, please contact Krista Osterthaler at osterthaler@poison.org.