Is It Healthy to Take Two One A Day Vitamins?

Vitamins and minerals are essential for good health, so you might assume that the more you get, the better. This is not the case, though. Some nutrients stay in your body for extended periods, and if you start doubling up and taking two doses of your multivitamin, these nutrients can build to toxic levels in your body. Unless otherwise recommended by your doctor, stick to just a single daily dose of a One A Day multivitamin.

Pill bottle lids
Close-up of sealed vitamin bottles. (Image: Design Pics/Design Pics/Getty Images)

B-Vitamin Surplus

The B vitamins convert food macronutrients into energy, create blood cells and help run your central nervous system. One A Day supplements typically contain close to, or 100 percent of, the recommended amount of each of the B vitamins. The majority of B vitamins aren’t harmful in excessive doses. However, in some cases, large amounts of B vitamins, particularly niacin and B-6, can negatively affect nerves. You may be jittery, feel a numb or tingling sensation, or have difficulty moving if you take too much.

Fat-Soluble Vitamin Woes

Fat-soluble vitamins are stored in the body, so your risk of taking too much increases. Having clear vision and healthy eyes requires you to get plenty of fat-soluble vitamin A in your diet. A single dose of a One A Day supplement has at least half of your daily recommendation. If you take two, you’ll get your entire days’ worth, but that's in addition to all the other vitamin A in your diet. Over time, a buildup of vitamin A damages your liver and weakens your bones. You’ll also get as much as double -- or more -- of your recommendation of vitamin D from a single dose of One A Day. That's more than quadruple your recommendation if you take two. Excessive vitamin D can cause tissues to harden. Your heart, kidneys and blood vessels can become damaged in the long run.

Iron Overload

Transporting oxygen to all cells is the primary job of iron. It’s possible to have too much, however. Initially you’ll feel nauseated, throw up and notice abnormal tarry stools. As iron toxicity worsens, your blood pressure drops, heart rate weakens and you could slip into a coma. This can be fatal. Avoid consuming more than 45 milligrams of iron daily, or the maximum safe allotment set by the Food and Nutrition Board of the Institute of Medicine. Daily multivitamins that have 100 percent of the daily value contain 18 milligrams of iron. Not all forms of One A Day have iron, though, like certain men's or gummy formularies, so read the label. If you take a double dose, you’ll get 36 milligrams of iron. While this isn’t over the maximum safe dosage, you could go over that amount when combining the vitamin supplement with iron-rich foods.

Other Concerns

One A Day supplements are packed with other nutrients that are equally harmful in large doses. Depending on which variety of multivitamins you take, you can get twice the daily value of trace minerals like chromium, manganese, copper, zinc and iodine. These trace minerals are crucial for biological processes that create hormones, regulate your blood sugar and make enzymes, among other functions. If you take two multivitamins, you might have some gastrointestinal upset in the beginning. But if you regularly double up on your dose, the high intake of minerals can make your heart beat irregularly, leave you chronically weak and make you lose consciousness. These dangerous side effects require immediate medical attention.

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