This Is What Happens When You Take Too Many Vitamins, According to Experts

Most people take vitamins expecting some sort of health boost. But sometimes they have the opposite effect — often as a result of the mega doses in multivitamin supplements, which are unregulated, meaning anything could be in that bottle you pick up at the supermarket. New Jersey-based dietitian Erin Palinski-Wade, author of the “2 Day Diabetes Diet,” suggests looking for a brand you can trust that has been third-party tested.

This isn’t a concern when you get vitamins from food. “It can be almost impossible to consume dangerously high levels of a specific nutrient from food alone,” Palinski-Wade says. But multivitamin doses can contain 1,000% of daily recommended values, and “it is possible to have too much of a good thing when it comes to supplements. Taking in more of a certain nutrient than your body needs can have a negative impact.”

Supplements are meant to supplement a balanced diet, not replace it, and Palinski-Wade recommends working with a registered dietitian to find the ones that match your needs and health goals – then making sure your doctor and pharmacist know what you’re taking, because some vitamins can interact with medications even in modest doses. 

There are two kinds of vitamins: Water soluble and fat soluble. Your body will generally eliminate excess water-soluble vitamins, which include all the B vitamins and vitamin C, in urine. But since the body can store large amounts of fat, fat-soluble vitamins A, E, D, and K, can build up. They are many of the vitamins and minerals we’ll look at for the effects of excessive intake. If you’ve had a bad experience with vitamins, tell us in the comments.

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Vitamin D is known as the sunshine vitamin because the body can make it in a process that involves the sun hitting uncovered skin — and with this method, or from food sources, it’s unlikely to get too much. (That’s more than 100 mcg, unless advised by a doctor.) Still, vitamin D is one of the most frequently supplemented because it can be difficult to get through sun and diet. Because it aids in calcium absorption, an excess can lead to a condition called hypercalcemia. Signs include pain, muscle weakness, nausea, excessive thirst, and kidney stones.

Related: Inexpensive Ways to Get More Vitamin D

Vitamin A deficiency is rare in the United States, where most people get enough from food sources. Adults shouldn’t have more than 3,000 mcg per day; if excessive vitamin A builds up in the liver, it can cause blurred vision, nausea, aching muscles and coordination problems. 

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Beta-carotene is a carotenoid that the body can convert into vitamin A. High doses of beta-carotene from supplements is linked to an increased risk of lung cancer. 

Related: The Surprising Side Effects of Eating Beets, According to Science

Vitamin E is an antioxidant that helps prevent cell damage from free radicals. There’s no risk of consuming too much vitamin E from food — adults shouldn’t take more than 1,000 mg per day — but high intake of alpha-tocopherol, a form of vitamin E in supplements, can cause hemorrhage and impact blood clotting.

Children, teenage girls, and people who are pregnant or menstruate are at highest risk of becoming iron deficient. Health care providers might recommend high doses of iron or supplements to people at risk of deficiency. In childbearing years, women should get 15 to 18 mg of iron. That number increases to 27 mg during pregnancy. For people without intestinal problems, excessive intake of iron from food sources is unlikely. Taking supplements with more than 25 mg of iron can lead to stomach issues such as constipation, nausea, pain, vomiting, and diarrhea. Excess iron can also reduce the absorption of the mineral zinc. In extreme cases, high doses of iron can lead to organ failure and coma.

Many Americans, especially children, consume less calcium than is needed for bone health, and postmenopausal women and anyone who avoids dairy is at an increased risk for a deficiency. Calcium is abundant in dairy products and is added to fortify cereal and some juices. Beyond that, excessive calcium can lead to low muscle mass, frequent urination, fatigue, constipation, weight loss, and heart arrhythmia. Some research suggests high calcium intake is linked to prostate cancer and heart disease.

Niacin is an important vitamin for energy and cell health. Most Americans get plenty through food sources, but some people supplement it hoping for an energy boost or to treat high cholesterol problems. Taking more than 30 mg of niacin per day can cause the skin on your face and chest to tingle, redden, warm or itch.

Vitamin B6 is important for brain development and metabolism. Long-term overconsumption — not more than 100 mg per day unless directed by a doctor — can lead to nerve damage, which would make it difficult to control movement. It’s also associated with patchy skin and sensitivity to sun. 

Folate is important for cell division. Most Americans get enough through diet, but a supplement is often recommended, particularly for people who are pregnant. High doses of folate can mask a vitamin B12 deficiency, which can lead to nerve damage. A possible link between high folic acid (a form of folate) and increased risk of colorectal cancer is being studied.