How much of a vitamin or mineral supplement should you take? Are your daily multivitamins enough, or should you worry about vitamin deficiency? Could you already be taking too much? It can be hard to tell -- especially with so many nutritional terms, abbreviations, and numbers out there. Here’s what you need to know.
To help people better understand the minimum and maximum doses for supplements, the Institute of Medicine has established some guidelines.
- The RDA (Recommended Dietary Allowance) and the AI (Adequate Intake) are the amounts of a vitamin or mineral you need to stay healthy and avoid nutritional deficiencies. They are 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 risking an overdose or serious side effects. For certain nutrients, the higher you go above the UL, the greater the chance of having problems.
Separate from the RDA and the UL, the FDA uses a different measurement of nutritional intake.
- 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 a person should get for optimum health from a 2,000 calories-a-day diet. The DV is sometimes the same as the RDA and sometimes not.
Although the details may be different, just remember that the RDA and DV are both designed to help us get the nutrients we need to prevent disease and avoid problems caused by malnutrition.
But many people take higher doses of specific supplements in the hopes of gaining other health benefits, like added protection against or treatment of disease.
Is taking doses higher than the RDA or DV safe? For many vitamins and minerals, yes. In some cases, doctors even recommend it. Take vitamin D, for instance. The RDA of vitamin D for a 60-year-old is 600 international units (IU). But for bone health, the National Osteoporosis Foundation recommends 800-1,000 IU for that age group.
Vitamins and Minerals: How Much Is Too Much?
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 and when it isn’t?
One way is to look for the UL (tolerable upper intake level) of a nutrient. The Institute of Medicine sets the UL after reviewing studies of that 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. However, some people develop neuropathy symptoms 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 taking just over three times the RDA of vitamin A would be taking 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 cause toxicity. Other risky supplements include the minerals iron and selenium.
- Supplements are designed to supplement the diet. Popping dietary supplements is not the answer to good health. Experts recommend eating a well-balanced, healthy diet and taking supplements to fill in any nutritional gaps. Or you can take a once-daily 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 figuring out whether you’re reaching the UL on a particular nutrient, you usually need to factor in 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 it is available on government web sites -- and a complete list of nutrients with ULs is listed 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 health care provider before taking supplements. Most supplements have possible drug interactions and side effects.
The good news is that the average person is unlikely to take so much of a nutrient that he or she will run into trouble. But it’s always wise to check in with a doctor before you start using a supplement regularly. And that’s definitely true if you’re using any supplement in high doses or for prolonged periods of time.