Health Options Alan Titchenal  & Joannie Dobbs                    Wednesday, October 23, 2002

Nutrients can be harmful when taken in megadoses

A couple of years ago, Maggie decided to get healthy. She started taking daily vitamin and mineral supplements and eating mostly food products that were promoted as having added vitamins and minerals. Whenever she went to the juice bar, she always asked for the extra vitamin and mineral powder.

For the first few months she felt energized, but over the past year she has not been feeling quite "right." Since she has kept with her program, she wonders what's wrong.

Question: Since Maggie is taking all the nutrients touted in magazines and television infomercials, why is she starting to feel poorly?

Answer: It's possible that she has been overdosing on nutrients. Today, so many products are fortified with extra vitamins and minerals that it is easier than ever to consume excessive amounts. Combining dietary supplements with fortified foods or adding that "extra vitamin shot" at the juice bar can potentially add up to too much of a good thing.

Q: Will someone feel negative side effects shortly after consuming excessive amounts of a nutrient?

A: With most nutrients, the negative effects of excessive intake do not occur for some time. Consequently, people experiencing a problem are unlikely to associate it with a practice they've been following for a year or two.

Q: Would a nutrient megadose be considered 10 times the Required Dietary Allowance?

A: No. A single percentage above the RDA does not work for all nutrients. For example, the upper tolerable intake limit for vitamin A is only two times the daily value, whereas the upper limit for vitamin B6 is 50 times the DV. On dietary supplement labels, which list a percentage of DV rather than upper limits, the maximum amount for vitamin A would read as 200 percent of DV; for vitamin B-6, 5,000 percent.

Q: Have upper-limit values been set for all nutrients?

A: No. Upper limits have not been established for all nutrients, either because the nutrient is known to be

rather safe at high dosage or, more likely, that there is too little known about the effects at high levels.

The chart above is a partial list of vitamins and minerals with established upper intake limits. Magnesium is not included because its UL of 350 mg/day is set to include only intake from supplements and drugs. Unlike magnesium naturally present in foods, too much from supplements and drugs can cause diarrhea. Consequently, the UL is about the same as the recommended intake from food alone.

Keep in mind that these "UL" numbers are not goals for nutrient intake, but rather represent the highest levels of intake that are unlikely to cause problems in normal, healthy people.