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Things like " RDA" or " DV" are just a few examples of an alphabet soup that's on many packages. But don't despair. We'll help you demystify supplement guidelines. Many of the terms you see on labels or supplement web sites can help you understand how much of the vitamin or mineral you should take. For example, here are some guidelines set up by the Institute of Medicine: The RDA ( Recommended Dietary Allowance) and the AI ( Adequate Intake) are the amounts of a vitamin or mineral you need to keep healthy and stay well-nourished. They're tailored to women, men, and specific age groups. The UL ( Tolerable Upper Intake Level) is the maximum amount of daily vitamins and minerals that you can safely take without risk of an overdose or serious side effects. For certain nutrients, the higher you go above the UL, the greater the chance you'll have problems. Separate from the RDA and the UL, the Food and Drug Administration uses a different measure for the nutrients you need: The DV ( Daily Value) is the only measurement you'll find on food and supplement labels. That's because space is limited, and there's a need for one single reference number. That number is the amount of a vitamin or nutrient that you should get for top health from a diet of 2,000 calories a day. The DV is sometimes the same as the RDA. Although the details may be different, remember that the RDA and DV are both set up to help you get the nutrients you need to prevent disease and avoid problems caused by lack of nutrition. Because high doses of some supplements can have risks, how do you know when it's OK to take more than the RDA or DV? One way is to look for the UL (tolerable upper intake level) of a nutrient. With many vitamins and minerals, you can safely take a dose much higher than the RDA or DV without coming close to the UL. For instance, the average person can take more than 50 times the RDA of vitamin B6 without reaching the upper limit. But some people develop symptoms of nerve pain with these higher levels of B6. So you should always be cautious. Here are some things to keep in mind: Some supplements are riskier than others. With some vitamins and minerals, the upper limit is pretty close to the RDA. So it's easy to get too much. For example, a man who takes just over three times the RDA of vitamin A would get more than the upper limit. High doses of vitamin A -- and other fat-soluble vitamins like E and K -- can build up in the body and become toxic. Other risky supplements include the minerals iron and selenium. Supplements are designed to be additions to your diet. Popping pills is not the answer to good health. Experts say you should eat a well-balanced diet and take supplements to fill in any nutritional gaps. Some people take a multivitamin with minerals for nutritional insurance. The UL is often the limit for all sources of a nutrient. It can include the amount you get from both food and supplements. So when you figure out whether you've reached the UL on a particular nutrient, take into account the food you eat. You won't find the UL on food nutrition labels or on your vitamin bottle. It's not a number that most people know about. But you'll see it on government web sites. And there's a complete list of nutrients with ULs at the end of this article. Most supplements don't have a UL -- or RDA or DV. The government has only set levels for a fraction of the vitamins and supplements available. For most of the supplements you see on the shelves, experts really don't know the ideal or maximum dose. Many nutrients, in too high a dose, can be dangerous. To be on the safe side, steer clear of the UL for any nutrient. And if you have a health condition, check with your doctor before you take supplements. He can tell you if they have side effects or interfere with other medicines you use. The Institute of Medicine has determined upper limits for 24 nutrients. This table is for adults ages 19 or older. It doesn't apply to women who are pregnant or breastfeeding, because they have different nutritional requirements. Vitamin or Mineral Recommended Dietary Allowance ( RDA) or Adequate Intake ( AI) Nutrients with AIs are marked with an (*) Upper Tolerable Limit ( UL) The highest amount you can take without risk Boron Not determined. 20 mg/day Calcium Age 19-50: 1,000 mg/day Women age 51+: 1,200 mg/day Men age 71+: 1,200 mg/day Age19-50: 2,500 mg/day Age 51 and up: 2,000 mg/day Chloride Age 19-50: 2,300 mg/day Age 50-70: 2,000 mg/day Age 70 and older: 1,800 mg/day 3,600 mg/day Choline ( Vitamin B complex) Women: 425 mg/day * Men: 550 mg/day * 3,500 mg/day Copper 900 micrograms/day 10,000 mcg/day Fluoride Men: 4 mg/day * Women: 3 mg/day * 10 mg/day Folic Acid ( Folate) 400 mcg/day 1,000 mcg/day This applies only to synthetic folic acid in supplements or fortified foods. There is no upper limit for folic acid from natural sources. Iodine 150 mcg/day 1,100 mcg/day Iron Men: 8 mg/day Women age 19-50: 18 mg/day Women age 51 and up: 8 mg/day 45 mg/day Magnesium Men age 19-30: 400 mg/day Men age 31 and up: 420 mg/day Women age 19-30: 310 mg/day Women age 31 and up: 320 mg/day 350 mg/day This applies only to magnesium in supplements or fortified foods. There is no upper limit for magnesium in food and water. Manganese Men: 2.3 mg/day * Women: 1.8 mg/day* 11 mg/day Molybdenum 45 mcg/day 2,000 mcg/day Nickel Not determined 1 mg/day Phosphorus 700 mg/day Up to age 70: 4,000 mg/day Over age 70: 3,000 mg/day Selenium 55 mcg/day 400 mcg/day Sodium Age 19-50: 1,500 mg/day * Age 51-70: 1,300 mg/day * Age 71 and up: 1,200 mg/day * 2,300 mg/day Vanadium Not determined 1.8 mg/day Vitamin A Men: 900 mcg/day Women: 700 mcg/day 3,000 mcg/day Vitamin B3 ( Niacin) Men: 16 mg/day Women: 14 mg/day 35 mg/day This applies only to niacin in supplements or fortified foods. There is no upper limit for niacin in natural sources. Vitamin B6 Men age 19-50: 1.3 mg/day Men age 51 up:1.7 mg/day Women age 19-50: 1.3 mg/day Women age 51 up: 1.5 mg/day 100 mg/day Vitamin C Men: 90 mg/day Women: 75 mg/day 2,000 mg/day Vitamin D ( Calciferol) Age 1-70: 15 mcg/day (600 IU, or international units) * Age 70 and older: 20 mcg/day (800 IU) * 100 mcg/day (4,000 IU) Vitamin E (alpha-tocopherol) 22.4 IU/day (15 mg/day) 1,500 IU/day (1,000 mg/day) This applies only to vitamin E in supplements or fortified foods. There is no upper limit for vitamin E from natural sources. Zinc Men: 11 mg/day Women: 8 mg/day 40 mg/day