The RDA is the amount of a vitamin or mineral found to be sufficient to meet the nutrient requirements of nearly all (98%) individuals in a group. AI is used in cases where RDAs haven’t been established because of insufficient data. AI is the amount believed to cover the needs of all individuals in a group.
A third set of numbers, the Tolerable Upper Intake Level (UL) is the amount of a nutrient above which the risk of adverse effects and toxicity increases. The UL represents vitamin or mineral intake from all sources, including food, water, and supplements.
DRIs have been established for 22 distinct life stage and gender groups. The %DV, while based on these numbers, combines many of these life stage and gender groups and excludes pregnant and lactating women to come up with numbers that apply to a wide population. For a list of all DRIs for each vitamin and mineral based on age and sex, go to www.iom.edu.
Many supplements contain additional, sometimes exotic ingredients (such as herbs or particular antioxidants) for a premium price. It is often unclear whether these ingredients offer benefits at all or, if they may have benefits, whether they offer them in the form they are found in, such as a tablet, pill, or capsule. Don’t pay a premium for a few additional ingredients in a multivitamin. Instead, make a point of eating a wide variety of fruits and vegetables, and you are bound to get the antioxidants that will help ensure good health.
The letters “USP” on a supplement label mean that the tablets meet the voluntary standards of the U.S. Pharmacopoeia and that they dissolve in a lab test designed to mimic what happens in your gut. A product with USP on the label is an added benefit. Manufacturers can also voluntarily pay to have their product tested for quality, purity, disintegration, and dissolution. For more information on testing, try the following Web sites:
- Council for Responsible Nutrition: www.crnusa.org
- NSF International, the Public Health and Safety Company: www.nsf.org
- United States Pharmacopeia: www.usp.org
- Consumer Lab: www.consumerlab.com
Form and timing
Although it is probably best to space your vitamin and mineral intake throughout the day for maximum absorbability, taking 3–4 pills per day just to get your daily dose isn’t very realistic for most people. If that’s the case for you, choose a brand that contains what you need in one pill. (This may not be possible for calcium supplements, which should contain no more than 500 milligrams per supplement.) If large pills are hard for you to swallow, go with chewable, liquid, or powder forms of vitamins.
In general, you should take vitamin and mineral supplements with a meal, since many nutrients are better absorbed when taken with food. However, if you have also been told to take any medicines with your meals, speak to your dietitian or another health-care provider about when to take vitamin and mineral supplements. Medicines should generally be taken a few hours apart from any supplements, just in case the two could interact. Iron, in particular, is known to have possible interactions with antacids, calcium supplements, and antibiotics and must be taken one to two hours apart from these substances.
Vitamins are necessary to ensure proper functioning within the body. Vitamins act as coenzymes, ensuring the proper functioning of enzymes.