Nowadays, everything from bottled water to orange juice seems to have souped-up levels of vitamins and minerals in it. That may sound like a way to help cover your nutritional bases, especially if your diet is less than stellar. But routinely getting an overload of vitamins and minerals can hurt you.
Too much vitamin C or zinc could cause nausea, diarrhea, and stomach cramps. Too much selenium could lead to hair loss, gastrointestinal upset, fatigue, and mild nerve damage.
While most people aren't getting megadoses, if you eat a fortified cereal at breakfast, grab an energy bar between meals, have enriched pasta for dinner, and take a daily supplement, you could easily be over the recommended daily intake of a host of nutrients.
Here's what you need to know to avoid overdoing it.
Supplements: Check the Dose
Chances are, the unfortified foods you eat aren't a problem. "It's pretty hard to overdo it from food alone," says Johanna Dwyer, RD, a senior research scientist with the National Institutes of Health's Office of Dietary Supplements.
So you'll want to think about the supplements you take and fortified foods or drinks.
"Most people don't realize there's no real advantage to taking more than the recommended amounts of vitamins and minerals, and they don't recognize there may be disadvantages," Dwyer says.
"If you're taking a supplement, stick to one that's no more than the daily value," Dwyer says. (Daily value is the amount of a vitamin or nutrient that a person should get for optimum health.)
Talk with your doctor about any supplements you're taking, including vitamins and minerals, and the dose you're taking, too. That way, your doctor can help you keep doses in a safe range.
"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.
Subtle Signs You're Getting Too Much
"I have not seen someone off the street who was taking a toxic level of vitamin A or D -- those are very unusual," says David Katz, MD, director of the Yale University Prevention Research Center in New Haven, CT, whose medical practice specializes in nutrition. "What I'm more likely to see is a person with a dosing level of supplements that's higher than optimal."
Scientists don't yet know if routinely getting a little bit too much of a vitamin or mineral (as opposed to a megadose) is a problem, Katz says.
"There might be hints of concern, but they would be very subtle signs," he says.
These fairly mild symptoms may include difficulty sleeping or concentrating, nerve problems such as numbness or tingling, or feeling more irritable -- depending on the nutrient that's going overboard.
The bigger concern, Katz says, is that we're "garnishing the food supply with overfortification."
He says manufacturers have shifted their focus from what they've taken out of food -- such as its fat, sugar, or salt -- to what they're putting in, whether it's vitamin D, probiotics, or omega-3 fats -- whatever nutrient is in vogue.
"When more and more foods are enhanced, it becomes impossible for consumers to know what dose they're getting over the course of a day," Katz says. "Clinicians have to realize we might be introducing new dietary imbalances because of this practice."
Three Nutrients to Watch
Dwyer says vitamin D, calcium, and folic acid are three nutrients you may get too much of, especially through supplements.
Adults who regularly far exceed the 4,000 international units (IUs) daily safe upper limit for vitamin D might may end up with serious heart problems.
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 cut the number of birth defects by 25% to 50%, it might have created other health concerns in people getting too much.
It's not 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.
There's no need to worry about foods that are naturally rich in folate.
"Most people can now get enough folic acid without having to rely on supplements," Dwyer says.
In fact, she says, "most people have no problem [with getting too much vitamins or minerals] if they start with food, which is the healthiest and safest way to get them."