Our Experts Answer Your Questions

What are vitamins?

Nutrition textbooks dryly define vitamins as organic compounds that the body needs in small quantities for normal functioning. Here’s the translation: Vitamins are nutrients you must get from food because your body can’t make them from scratch. You need only small amounts (that’s why they are often referred to as micronutrients) because the body uses them without breaking them down, as happens to carbohydrates and other macronutrients.

So far, 13 compounds have been classified as vitamins. Vitamins A, D, E, and K, the four fat-soluble vitamins, tend to accumulate in the body. Vitamin C and the eight B vitamins—biotin, folate, niacin, pantothenic acid, riboflavin, thiamin, vitamin B6, and vitamin B12—dissolve in water, so excess amounts are excreted.

The “letter” vitamins sometimes go by different names. These include:

  • Vitamin A = retinol, retinaldehyde, retinoic acid
  • Vitamin B1 = thiamin
  • Vitamin B2 = riboflavin
  • Vitamin B6 = pyridoxine, pyridoxal, pyridoxamine
  • Vitamin B12 = cobalamin
  • Vitamin C = ascorbic acid
  • Vitamin D = calciferol
  • Vitamin E = tocopherol, tocotrienol
  • Vitamin K = phylloquinone

To learn more, read 5 Quick Tips for Getting the Right Vitamins.

What should I look for in purchasing a multivitamin?

Look for a multivitamin that has 100 percent of the Dietary Reference Intakes (DRI) for most vitamins. Be careful of supplements that have greater than 200 percent or 300 percent of the DRI, and be especially cautious of ones that have 1,000 percent of the DRI. In such large does, you will excrete out what you don’t need for water-soluble vitamins such as vitamin C, and may experience liver damage or other toxic side effects for large doses of fat-soluble vitamins, such as vitamin A. One exception to this rule is vitamin D, as many people need more than the DRI of 600 IU. The best available evidence shows optimal intakes are higher, at least 800–1,000 IU for adults, so if your multi only has 400 IU of vitamin D, consider taking an extra supplement. Many people may need 2,000 IU per day (or more) for adequate blood levels, particularly if they have darker skin, spend winters at higher latitudes (such as the northern U.S.), or spend little time in the sun. If you fall into one of these groups, which would include most of the U.S. population, taking 2,000 IU is reasonable and well within the safe range. As always, it’s a good idea to discuss use of supplements with your doctor, and he or she may want to order a vitamin D blood test.

To learn more, read 5 Quick Tips for Getting the Right Vitamins.

Are time-release vitamins better for you?

The idea behind time-release vitamins is that they provide a consistent amount of vitamins into your blood stream over the course of a day. However, time-release vitamins, unlike some time-release prescription medications, seem not to be useful and end up costing more.

What type of vitamin D supplement is best?

Two forms of vitamin D are used in supplements: vitamin D2 (“ergocalciferol,” or pre-vitamin D) and vitamin D3 (“cholecalciferol”). Vitamin D3 is chemically indistinguishable from the form of vitamin D produced in the body, and there’s evidence that it may be more effective than vitamin D2 at raising vitamin D levels in the blood. That’s why some scientists recommend looking for vitamin supplements that contain vitamin D3. Other scientists believe that vitamin D2 and vitamin D3 are similarly effective. Indeed, high dose vitamin D2 is available by prescription, and doctors regularly prescribe it to restore vitamin D levels in people who are deficient. As it turns out, the marketplace may answer the vitamin D question for you: More and more supplement makers offer vitamin D3 in their products.

To learn more about vitamin D, read Vitamin D and Health.

What’s the difference between folate and folic acid?

Folate is the form of the B vitamin found naturally in foods, and it is the generic term for the vitamin. Folic acid is the form of the vitamin that is added to multivitamins and to fortified foods (such as white flour and products made with white flour, breakfast cereals, “energy” or protein bars, and so on).

During digestion, the body converts folate into folic acid, which is then absorbed and used in multiple ways. Since vitamin pills and fortified foods contain folic acid, they can “skip” this conversion step, making folic acid more readily available to the body than folate from food.

To reflect this difference in availability to the body, government recommendations for folate are given in “Dietary Folate Equivalents,” or DFEs: One microgram of folate from food equals 1 DFE; 1 microgram of folic acid from fortified foods, or from a vitamin pill taken with food, equals approximately 1.7 DFEs; 1 microgram of folic acid from a vitamin pill taken on an empty stomach equals 2 DFEs.

To learn more about folate and other B Vitamins, read Three of the Bs: Folate, Vitamin B6, and Vitamin B12.

Terms of Use

The aim of the Harvard T.H. Chan of Public Health Nutrition Source is to provide timely information on diet and nutrition for clinicians, allied health professionals, and the public. The contents of this Web site are not intended to offer personal medical advice. You should seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this Web site. The information does not mention brand names, nor does it endorse any particular products.