Unlike other vitamins, most of the vitamin D you need comes from daily exposure to the sun's rays and not from food. Even though the sun is a natural source of vitamin D, deficiency rates are rising because of too much time spent indoors. Many doctors and health-care professionals recommend a daily vitamin D supplement, but it is difficult to know which is best for you.
Natural Vitamin D
Vitamin D plays several roles in the body, such as maintaining bone health and muscle flexibility. Most people can get all they need from just 10 to 20 minutes of daily sun exposure. When the sun hits the skin, dietary cholesterol is converted into vitamin D. People with darker skin or those who live further from the equator may need longer exposure to get enough vitamin D. Also, in order to make vitamin D, the skin needs to be directly in the sun and not blocked by sunscreen or cover-ups.
Vitamin D in supplements is found in either the D2 or D3 form. Vitamin D3 is derived from two sources -- fish oil and sheep lanolin. Vitamin D3 from fish oil comes from the skin of fatty fish such as salmon or tuna, which naturally contain vitamin D. Lanolin is a waxy substance secreted by glands found in a sheep’s skin. Vitamin D3 from either source is the exact same form of vitamin D found in our bodies and, as a supplement, is the best absorbed.
Vitamin D2 is generally used to fortify milk or other foods and is made from yeast or other plant matter. Many experts believe that D2 is not well absorbed or utilized by the body because it is from plants and not the type of vitamin D the body naturally makes. The body can convert D2 to D3, but it may not be as efficient, especially if you are trying to correct a vitamin D deficiency. If you are a vegetarian or vegan, however, vitamin D2 is the only vegan source of vitamin D.
Tips for Getting Vitamin D
The recommended dietary allowance for vitamin D is 600 international units. Most foods are a poor source of vitamin D. The best way to get enough vitamin D is to spend 5 to 30 minutes in the sun at least twice a week without any sunscreen or cover-ups. If you have a deficiency, determined via a blood test, your doctor may recommend a supplement or give you a prescription for high dose vitamin D. The upper limit for vitamin D is 4,000 IU, unless otherwise directed by a physician.
Ana Johnson is a registered dietitian with professional experience in clinical nutrition, weight loss and medical nutrition therapy. She has also covered nutrition for various online publications, including Smarty Pants Vitamins and HUM Nutrition. Johnson holds a Master of Science in clinical nutrition.