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
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.