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?
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.