Sometimes it’s hard to keep all the information about vitamins straight. Many have more than one form, each form has a different name and each may have a diverse job to fill. Vitamin D, for example, comes in five forms, but the ones most relevant to your health are vitamins D2 and D3. You don’t need to worry about which one you consume because they all convert into the same hormone in your body.
About Vitamin D
Vitamin D is the generic name used to represent all forms of vitamin D. When you see “vitamin D” listed on a label, it may mean vitamin D2, vitamin D3 or both. D2 and D3 are natural substances, but each one can also be synthesized commercially, and used in supplements or to fortify foods. The bottom line is that you can count on both of them because they fill identical roles in your body. Vitamin D2 is the form produced by mushrooms when they're exposed to sunlight.
Your skin makes vitamin D3 from ultraviolet light, but it must be converted into other forms in the liver and kidneys before it becomes an active hormone. The amount of vitamin D produced by your skin depends on a lot of variables, from the season and cloud cover, to your age, weight and how much skin is covered by clothing. Sunscreen significantly reduces the production of vitamin D, but don’t stop using it. Protecting your skin from cancer is so important that the American Academy of Dermatologists recommends using sunscreen and taking supplements if necessary to be sure you get enough vitamin D.
The most important reason to get your daily vitamin D is to keep your bones strong. Even if you consume plenty of calcium, it can’t be absorbed into your bloodstream unless you also have vitamin D. This relationship between vitamin D and calcium doesn’t just impact your bones. Your body needs calcium to keep nerves and muscles working. In fact, muscle weakness and pain can be one sign of not getting enough vitamin D. Your immune system also counts on vitamin D, where it helps regulate the system and stimulates the growth of cells that destroy bacteria and toxins.
The best way to get your vitamins is through a balanced diet, but vitamin D presents a unique challenge because it’s not a natural nutrient in most foods. Eggs and liver contain a small amount. Mushrooms may be a source, but the amount they provide depends on their exposure to the sun. Fatty fish are the only good natural sources. A 3-ounce serving of salmon, herring and mackerel supplies more than 30 percent of your daily allowance. Most Americans get their vitamin D from enriched foods, such as cereal, milk and other dairy products. The recommended daily allowance is 600 international units. If you take supplements, don’t exceed 4,000 international units, because excessive vitamin D can be toxic.
- Linus Pauling Institute: Vitamin D
- Harvard School of Public Health: Low Vitamin D: What Increases the Risk?
- American Academy of Dermatology and AAD Association: Position Statement on Vitamin D
- Endocrinology and Metabolism Clinics of North America: Vitamin D and the Immune System: New Perspectives on an Old Theme
- National Academies Press: Dietary Reference Intakes for Calcium and Vitamin D