Our bodies need vitamins and minerals for functions such as helping our muscles work properly, maintaining immunity, fortifying our bones, and breaking down the food we eat. Most healthy individuals don’t need any nutritional supplements if they eat a variety of foods — including fruits, vegetables, whole grains, legumes, low-fat dairy products, lean meats and fish. And for most of us, eating a well-balanced meal is much healthier than a multivitamin. Some of us, however, might benefit from a nutritional supplement such as vitamin D, vitamin B12, magnesium or iron. But there’s no reason to get more than you need, and some nutrients can be dangerous in large amounts. 

Why should I be concerned about vitamin and mineral safety?

In 2019, vitamins were responsible for 56,361 toxic exposures in the United States, and other dietary supplements caused 69,618 toxic exposures, as listed by the National Poison Data System (NPDS). While it’s true that the number of serious medical outcomes associated with vitamin toxicity is low, a scary and expensive ER visit — and truly alarming, uncomfortable, even painful symptoms (nausea, abdominal pain, vomiting) — can occur when someone “overdoses” on a vitamin or mineral supplement. 

Supplement ingredients sold in the U.S. before October 15, 1994 are not required to be reviewed by the Food and Drug Administration (FDA) for their safety before they are marketed because they are presumed to be safe based on their history of use by humans. For a new dietary ingredient (one not sold as a dietary supplement before 1994) the manufacturer must notify FDA of its intent to market a dietary supplement containing the new dietary ingredient and provide information on how it determined that reasonable evidence exists for safe human use of the product. However, manufacturers do not have to prove to FDA that a supplement is effective or safe, unlike the rigorous process demanded of makers of pharmaceuticals. Once a dietary supplement is marketed, the FDA has to prove that the product is not safe in order to restrict its use or remove it from the market. 

Can you consume toxic levels of vitamins or minerals in food? 

It’s extremely rare to reach a toxic consumption level of a vitamin or mineral from natural food sources. But some foods are “fortified” with lab-produced nutrients — like some cereals, milk, protein bars, bread, and fruit juices. For example, orange juice often contains added calcium or vitamin D. But even with fortified foods, occurrences of ingesting too many added supplements are few. 

Supplements vs. whole foods

Supplements can't replicate all of the nutrients and benefits of whole foods, such as fruits and vegetables. Plus, whole foods contain a mix of minerals, enzymes, fiber, perhaps beneficial antioxidants and other substances — some of which may help your body absorb and use nutrients. Thus, eating a well-balanced meal is much healthier than a multivitamin, and it’s not clear whether vitamins and minerals have the same effect in the body when taken in supplement form.

As aptly stated by the National Institute of Health (NIH), “Dietary supplements are not intended to treat, diagnose, mitigate, prevent, or cure disease. In some cases, dietary supplements may have unwanted effects, especially if taken before surgery or with other dietary supplements or medicines, or if you have certain health conditions. Supplements should not replace prescribed medications or the variety of foods important to a healthful diet.”

So why take supplements at all?

For some people, supplements may be a useful way to get nutrients they might otherwise lack. According to Mayo Clinic, supplements (or fortified foods) may be appropriate if you:

• Are pregnant or are trying to get pregnant
• Are age 50 or older
• Have a poor appetite or have trouble getting nutritious foods
• Follow a diet that excludes entire food groups
• Have a medical condition that affects how your body digests nutrients, such as chronic diarrhea, food allergies, food intolerance, or a disease of the liver, gallbladder, intestines or pancreas
• Have had surgery on your digestive tract that affects how your body digests nutrients

Talk to your medical provider first, and be sure to ask about dosage, side effects and possible interactions with any medications you take. 

General rule of thumb: Unless advised by a doctor, you should never take more than the recommended daily amount (RDA) of multivitamins or vitamin supplements. While some diseases and conditions can be helped by elevated vitamin or mineral use, a healthcare professional should always be consulted before following high-dose regimens. 

What are the symptoms of a vitamin or mineral overdose?

While symptoms vary depending on which vitamin or mineral has been consumed excessively, the most common initial symptoms are nausea, vomiting and/or diarrhea (which we’ll call, as a group, GI discomfort). See the additional, specific symptoms correlated with each substance, in the sections below.

Which vitamins are the most toxic if consumed excessively?

Vitamins fall into two groups: those that are water-soluble, and those that are fat-soluble. Your body can excrete large amounts of water-soluble vitamins, so most of them are “hard to overdose on.” However, your body holds onto fat-soluble vitamins in fatty tissue and the liver, so they can be toxic at high levels. There are only four fat-soluble vitamins: A, D, E and K. The most dangerous at high doses: A, E and K. 

The following brief descriptions discuss each substance’s health benefit generally, foods containing it naturally, symptoms and outcomes from excessive consumption, and the recommended upper limit (UL) for adult men to ensure no toxicity; readers seeking more specific information, e.g., recommended daily amounts (RDAs) and ULs for different population groups, should refer to these NIH Factsheets.  

Vitamin A: 

• Important for visual health and immunity 
• There are two types: (1) preformed vitamin A is found in meat, poultry, fish, and dairy products; (2) provitamin A, is found in fruits, vegetables, and other plant-based products — including carrots, sweet potatoes, watermelon and cantaloupe. The most common type of provitamin A in foods and dietary supplements is beta-carotene, and you typically get plenty of it from a balanced diet.
• At toxic doses vitamin A can cause headache and skin rashes, and in severe cases could lead to lung cancer. It can also cause birth defects in babies if the pregnant mother takes too much of vitamin A supplements. 
• Adult men UL: 3,000 micrograms/day

Vitamin D:

• In combination with calcium, vitamin D fortifies your bones, and it also plays a role in immune function, improves asthma and depression, and boosts mood. 
• Getting a little bit of sunshine each day enables your skin to manufacture enough vitamin D, and it is also contained in foods including fortified milk, cereal, orange juice; and fatty fish (e.g., salmon). Yet, as many as one in five Americans are deficient in it — which your medical provider can determine with a simple blood test. So a supplement may make sense; yet, newer studies question whether vitamin D supplements have any efficacy in preventing disease. 
• You can definitely be harmed by too much vitamin D, and symptoms beyond GI discomfort include muscle weakness, confusion, pain, loss of appetite, dehydration, excessive urination and thirst, and kidney stones. Extremely high levels of vitamin D can cause kidney failure, irregular heartbeat, and even death. High levels of vitamin D are almost always caused by consuming excessive amounts of vitamin D from dietary supplements. You cannot get too much vitamin D from sunshine because your skin limits the amount of vitamin D it makes. 
• Adult UL: 100 micrograms/day

Vitamin E:

• Important for vision, reproduction, and the brain/blood/skin health, vitamin E also has antioxidant properties.
• Found in oils, nuts, green vegetables; generally easy to get enough from a balanced diet.
• High doses of vitamin E from supplements might increase the risk of bleeding (by reducing the blood’s ability to form clots after a cut or injury) and of serious bleeding in the brain (known as hemorrhagic stroke), so avoid high quantities especially if you’re on blood thinners like warfarin, heparin, etc.
• Adult UL: 1,000 milligrams/day

Vitamin C:

• Supports normal growth and healing; helps iron absorption.
• Plentiful in most fruits and many vegetables.
• Taking too much vitamin C can cause diarrhea, nausea, and stomach cramps. In people with a condition called hemochromatosis, which causes the body to store too much iron, high doses of vitamin C could worsen iron overload and damage body tissues.One study found that men who took vitamin C pills had a higher risk for developing kidney stones.
• Adult UL: 2,000 milligrams/day

Vitamin B3 (niacin):

• Important for the development and function of the cells in your body, and helps turn the food you eat into the energy you need.
• Present in most animal foods, some nuts and legumes; most Americans get plenty from a balanced diet.
• High doses can lead to high blood pressure, abdominal pain, impaired vision, and liver damage.
• Adult men UL: 35 milligrams/day 

Vitamin B6:

• Needed for more than 100 enzyme reactions involved in metabolism, brain development during pregnancy and infancy, and immune function.
• Plentiful in animal foods, starchy vegetables (like potatoes) and fruits. Americans are rarely deficient. 
• Taking high levels of vitamin B6 from supplements for a year or longer can cause severe nerve damage, painful skin patches, extreme sensitivity to sunlight, nausea, and heartburn. Symptoms usually stop when supplement consumption is curtailed.
• Adult UL: 100 milligrams/day

Vitamin B9 (folate):

• Needed to make DNA and other genetic material, and for your cells to divide.
• Found in beef liver; vegetables; fruits; nuts, beans and peas; and a host of fortified breads and other foods. Most of us get enough from food, but women and teen girls who could become pregnant are advised to take a supplement.
• Taking large amounts of folate supplements might hide a vitamin B12 deficiency because these supplements can correct the anemia that the vitamin B12 deficiency causes, but not the nerve damage that the vitamin B12 deficiency also causes. The vitamin B12 deficiency can lead to permanent damage of the brain, spinal cord, and nerves. Large doses of folate supplements might also worsen the symptoms of vitamin B12 deficiency. High doses of folic acid might increase the risk of colorectal cancer and possibly other cancers in some people. 
• Adult UL: 1,000 micrograms DFE/day

Calcium:

• Plays a critical role in building and maintaining healthy bones.
• In addition to most dairy foods, calcium can be obtained from consuming grass fed, organic Greek yogurt; leafy greens like kale and spinach; salmon and sardines; and a host of fortified juices and other foods. Postmenopausal women and people who don’t drink milk or eat other dairy products may not get enough calcium from foods.
• Excess calcium can cause muscle pain, mood disorders, abdominal pain and kidney stones. Researchers believe that without adequate vitamin D to help absorb it, the extra calcium settles in the arteries instead of the bones. Abnormal heart rhythms and a high risk of death from heart disease have been associated with excessive calcium intake, but this may be brought on by other health conditions.
• Adult male UL: 2,500 milligrams/day

Magnesium:

• Important for many processes in the body, including regulating muscle and nerve function, blood sugar and blood pressure levels; and making protein, bone, and DNA.
• Found naturally in many foods such as legumes, nuts, seeds, whole grains, and green leafy vegetables; and is added to some fortified foods, such as milk, yogurt, breakfast cereals. Many people in the U.S. are deficient in magnesium, particularly men over 70 and teenagers.
• High intakes of magnesium from dietary supplements and medications can cause diarrhea, nausea, and abdominal cramping. Extremely high intakes of magnesium can lead to irregular heartbeat and cardiac arrest.
• Adult UL: 350 milligrams/day.

Iron:

• Needed for growth and development, to make hemoglobin and myoglobin, and to make some hormones. Plays a key role in younger women’s diets for menstrual cycles and pregnancy, but the recommendations for iron after menopause significantly decrease.
• Found naturally in lean meat, seafood and poultry; also in white beans, lentils, spinach and nuts. Vegetarians need almost twice the RDA because the body doesn’t absorb the type of iron in plant foods as well as the iron in animal foods. Most of us get enough from a well-balanced diet.
• Taking high doses of iron supplements (especially on an empty stomach) can cause an upset stomach, constipation, nausea, abdominal pain, vomiting, and fainting. High doses of iron can also decrease zinc absorption. Extremely high doses of iron (in the hundreds or thousands of mg) can cause organ failure, coma, convulsions, and death. 
• Adult male UL: 45 milligrams/day

Which vitamins should those with diabetes avoid?

Many, but not all, individuals with diabetes experience low levels of certain vitamins and minerals, such as vitamins A, many of the B vitamins, C, D, E, and K; and chromium, selenium, magnesium, zinc and iron. So it sounds tempting for people with diabetes to consider nutritional supplements of various types.

However, after reviewing the evidence, leading clinicians have not reached a consensus on the  recommendation of supplements for those with diabetes, as this clinical review summed up — with the exception of B12 for those with type 2 diabetes (T2D) who are also taking the medication metformin: 

• The absorption of folic acid (B9) and vitamin B12 are linked, and they are decreased by the prolonged use of metformin, a first-choice drug for treating uncomplicated T2D. 
• Research has shown that nerve damage due to diabetes is worse in patients who have vitamin B12 deficiency, so supplementation with vitamin B12 has been found to improve the symptoms in patients with severe diabetic neuropathy. 
• Fortunately, vitamin B12 has not been found to cause any harm or side-effects at normal doses or even up to the UL. However, as with everything, you should avoid taking very high doses of vitamin B12, and consult with your medical provider first.

Of the vitamins and minerals that scientists are studying because they may prove beneficial in the prevention of treatment of diabetes, the following are of great interest — although fully conclusive research has yet to be published:

• There is some evidence, but it’s still considered weak, that vitamin K could lower the risk of developing T2D, and vitamin K supplementation rarely results in toxicity risk. 
• Chromium also is linked to more efficient use of glucose, but more research is needed.
• Magnesium is being heavily studied right now because people with higher amounts of magnesium in their diets tend to have a lower risk of developing type 2 diabetes. Magnesium helps the body break down sugars and might help reduce the risk of insulin resistance (a condition that leads to diabetes). Scientists are studying whether magnesium supplements might help people who already have type 2 diabetes control their disease, but more research is needed to better understand whether magnesium can help treat diabetes.

Despite interest in supplementation with each of the following, the jury is still out on all of them, or they are contraindicated outright — so those with diabetes should refrain from excessive supplementation with the following vitamins and minerals unless a medical provider has prescribed them for a specific reason:

• Vitamin A supplements show no efficacy if the person with diabetes also has cardiovascular or obesity risks, and high doses are risky.
• Vitamin B3 (niacin) is taken by some people to raise HDL (“good”) cholesterol, but it can also affect your diabetes management, according to the American Diabetes Association. Niacin raises fasting glucose levels (your blood sugar levels when you are not eating), so the risks may outweigh the benefits. 
• Vitamin C and E supplements won’t ward off diabetes and diabetes complications. Until the research shows a clear benefit, it’s best to pass on these. And we’ve discussed, previously, toxicity risks are high for E at high doses.
• Vitamin D: While a 2019 meta-analysis concluded that supplementation improves indices of glycemic control in patients with diabetes mellitus, another 2019 study published in The New England Journal of Medicine found that taking vitamin D does not prevent the development of type 2 diabetes in most people at high risk for the disease. As for people who already have diabetes, the research is similarly less than compelling. Furthermore, an NIH factsheet states that clinical trials in people with and without diabetes show that supplemental vitamin D does not improve blood sugar levels, insulin resistance, or hemoglobin A1c levels (the average level of blood sugar over the past 3 months). As stated previously, vitamin D toxicity can happen if you take too much of it in supplement form, whereas your body self-regulates natural sources of D (e.g., from sunlight). 

How can I find out if a vitamin supplement is right for me? 

To get a list of all vitamins and minerals and how much you need, check out the free online tool from the U.S. Department of Agriculture. Just input a few pieces of information about yourself including your age, height, and weight. You also can get a list of your daily calorie, protein, and other nutritional needs. 

For the safest products, look for the United States Pharmacopeia (USP) seal on the bottle. Products sold as dietary supplements come with a Supplement Facts label that lists the active ingredients, the amount per serving (dose), as well as other ingredients, such as fillers, binders, and flavorings.

Most importantly, do not self-diagnose any health condition. Work with your medical provider to determine how best to achieve optimal health and to determine if a supplement is advisable, especially if you take any medicines or other dietary supplements or if you have any health conditions.

In addition to talking with your healthcare provider about dietary supplements, you can search on-line for information about a particular supplement. It is important to ensure that you obtain information from reliable sources such as:

• ODS dietary supplement fact sheets
• Nutrient Recommendations: Dietary Reference Intakes (DRI) and Recommended Dietary Allowances (RDA)
• Dietary supplement warnings and safety information from the U.S. Food and Drug Administration
• Consumer information from the Federal Trade Commission

Key Takeaways

Most healthy individuals get all the important vitamins and minerals they need from a well-balanced diet of fruits, vegetables, whole grains, legumes, low-fat dairy products, lean meats and fish. If you’re one such individual, you don’t need a multivitamin or any other nutritional supplement, for that matter. A minority of us, however, might benefit from a nutritional supplement if, after talking with a medical provider, it is determined that we could be deficient in one or more vitamins or minerals. But there’s no reason to get more than you need; in fact, quite a few nutrients can be dangerous if consumed in excessively large amounts.