Do you track multivitamins?

. . . A few rare cases in medical journals have described, for example, an overload of vitamin A in a person who ate polar bear liver, a meat with extremely high amounts of this vitamin. Signs of a surplus of vitamin A may include nausea, blurred vision, and dizziness.

And if you eat handfuls of Brazil nuts every day, you could be way over the Tolerable Upper Intake Limit (the maximum per day that is unlikely to cause harm, as determined by the Institute of Medicine) for selenium. Just one ounce of Brazil nuts contains 544 micrograms of selenium. The Tolerable Upper Intake Limit is 400 micrograms per day -- and less if you're younger than 14.

Since polar bear liver and sacks of Brazil nuts are probably not on your menu, you'll want to think about the supplements you take and fortified foods or drinks.

"If you're taking a basic multivitamin, there's no need to fear taking too much," says Andrew Shao, PhD, senior vice president of scientific and regulatory affairs for the Council for Responsible Nutrition, a trade group for the supplements industry.

"Most multivitamins have such a wide margin of safety that even when you're combining them with fortified foods, it's still not going to cause you to keel over," Shao says.

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Three Nutrients to Watch

Dwyer says vitamin D, calcium, and folic acid are three nutrients you may get too much of through a combination of food and supplements.

Adults who regularly far exceed the 4,000 international units (IUs) daily safe upper limit for vitamin D might be setting themselves up for kidney stones down the road -- a health problem that may also occur with excessive intake of calcium, whose upper limit range is 2,000-2,500 milligrams daily.

Folic acid is added to enriched grain products -- white flours, pasta, rice, breads, and cereals -- to help prevent birth defects in babies due to folic acid deficiency in pregnant women..

While folic acid fortification has successfully cut the number of birth defects by 25% to 50%, it might have created other health concerns in people getting too much. (There's no need to worry about foods naturally rich in folate.)

It's not that hard to get more than 1,000 micrograms of folic acid a day (the safe upper limit for adults) from fortified foods and supplements on a regular basis. Doing so might hide the signs of a vitamin B12 deficiency in older adults. Vitamin B12 deficiency can sometimes lead to permanent nerve damage if left untreated.