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Apr 06, 2025

The Dangers of Too Many Supplements, According to Science

While you can enhance your healthy diet with the right choices, too much of a good thing is not always best. Maria Laura is EatingWell's Editorial Manager for Nutrition & News. As part of the

While you can enhance your healthy diet with the right choices, too much of a good thing is not always best.

Maria Laura is EatingWell's Editorial Manager for Nutrition & News. As part of the nutrition team, she edits and assigns nutrition-related content and provides nutrition reviews for articles. Maria Laura's education, experience and clinical hours from Mexico are equivalent to that of a U.S. credentialed registered dietitian. She is an almond butter lover, food enthusiast and has over seven years of experience in nutrition counseling.

Design elements: Abbey Littlejohn and Getty Images. EatingWell design.

Key Takeaways

St. John’s wort. Iron. Calcium. At the peak of my illness with Lyme disease, my mother doled out more than 20 supplements a day, which I had to choke down with the meager meals I could force myself to eat. I wasn’t just suffering from typical Lyme disease symptoms—the bacteria that causes the infection had spread to my central nervous system, causing what is called neurological Lyme disease.

In addition to seeing a Lyme specialist and a neurologist, I regularly saw a naturopath who prescribed the boatload of supplements that he assured us would help me to walk again and recover my flagging cognitive function. But it turns out that megadosing me on vitamins I was already getting from food may have been making me sicker than I already was.

That was more than 20 years ago. Today, the science of supplements has been more carefully examined. With hindsight on my side, I wondered—was it my Lyme disease, the excessive supplementation or a combination thereof that kept me totally disabled for almost seven years?

Fortunately, not everyone can relate to the extent of my experience. And while most people aren’t taking 20 supplements daily, I wouldn't be surprised if some come close.

We are inundated with talk of dietary supplements daily. Maybe it’s products being hawked by a peppy wellness influencer in your social feed, or on the ad break during your favorite podcast. Or perhaps family or friends bring up the supposed latest and greatest supplement during dinner. The idea that healthy eating isn’t enough is everywhere.

Can supplements be helpful when used appropriately, or should I toss the few that I still keep in my cupboard and instead stick to a balanced diet to get the nutrients my body needs? And what does science say are the real dangers of taking too many supplements? I talked to a medical toxicologist, a hepatologist (liver specialist) and a dietitian to understand more, and to avoid further pitfalls of the booming yet unchecked supplement industry.

What exactly qualifies as a dietary supplement? In essence, it’s anything you ingest that isn’t food or medication. According to the Food and Drug Administration, supplements can include vitamins, including elemental ones like A, B, C and D; botanicals or herbs, elderberry or ginger, botanical compounds (think green powders); minerals, such as calcium and magnesium; and even live microbials, usually referred to as “probiotics.”

“When we’re looking and thinking about supplementation, it’s to enhance the diet; so if there is a true deficiency, then supplementation would be warranted. It should not replace having a healthy diet,” explains Beth Czerwony, M.S., RD, CSOWM, LD, an outpatient dietitian for the Center for Human Nutrition at the Cleveland Clinic in Ohio.

In other words, nutritional supplements cannot and should not replace meals, or for that matter, medicines. Their name says it all. However, David W. Victor III, M.D., the interim chief of hepatology at Houston Methodist in Texas, says not to discount their power: “Every supplement can be considered in some way a drug because it is a substance taken for a therapeutic purpose.”

Victor explains that, just like food or medicine, supplements are broken down in the digestive tract and absorbed into the bloodstream, which transports them to the appropriate tissues.

The reasons that people take supplements are as varied as our bodies themselves. I did it to potentially fill in dietary gaps, as well as to try to improve my ill health. It’s common to take vitamin C or echinacea with the expectation of supporting immunity during cold and flu season. Others might turn to vitamin B12 with the hope that it will boost energy levels or help improve workouts. The common factor is that consumers are seeking something they believe they can’t get from food or from the medications prescribed by their doctors. And the trend is only growing, with 1 in 3 adults in the United States and Europe taking at least one supplement per day.

Under current laws, as laid out by the Dietary Supplement Health and Education Act in 1994, part of the Federal Food, Drug and Cosmetic Act, the FDA has no authority over dietary supplements, meaning it doesn’t regulate them. Instead, it’s up to supplement companies to provide oversight and ensure the safety of their products, which comes with some risks. For instance, a supplement may not contain what it says it does, or may contain an ingredient that isn’t listed. Even more so, anyone could sell a supplement without proving its effectiveness. However, if the FDA deems a supplement on the marketplace to be unsafe, it can request that the company recall the product.

While some supplements can be dangerous due to drug interactions or because of a person’s underlying health problems, usually, their toxicity lies in taking too many of them. As John W. Downs, M.D., M.P.H., FACP, FACOEM, director of the Virginia Poison Center at VCU Health in Virginia, puts it, “Just like with all medications, it is important to recognize that more isn’t always better. Excessive intake of certain vitamins and nutritional supplements can be just as harmful as taking medications in excess of the prescribed doses.”

And the supplements that can be toxic when you take too much of them aren’t just obscure ingredients. Downs says that they include the basics. For example, a high dose of vitamin A could cause liver damage or increased pressure on the brain. Many of us don’t get enough vitamin D from food, and it’s estimated that around 40% of the U.S. population may have vitamin D insufficiency. But taking too much can lead to elevated serum calcium concentrations, which can cause kidney dysfunction and mental status changes.

Vitamin A and vitamin D are both fat-soluble. Czerwony says that means your body stores them in fat cells, rather than getting rid of them through urination, as with water-soluble ones (including most B vitamins and vitamin C). Fat-soluble vitamins can accumulate in fat stores over time and result in “super-high levels and side effects,” she says.

Since Victor deals with the liver every day, he’s especially well-positioned to have seen which supplements can wreak havoc. While turmeric supplements have been shown to be pretty safe in the short term for most people, he mentions this supplement and its active compound, curcumin, have caused liver damage in some people at doses as low as 500 milligrams daily (the lowest dose commonly found in turmeric supplements). It’s important to note that turmeric supplements contain much higher concentrations of curcumin compared to the spice per se. Plus, curcumin in food is much less bioavailable (how much is absorbed and used by your body) compared to the supplement.

Another example is green tea. Green tea extract, reputed for its antioxidant properties, may also cause injury to the liver when taken in excess, he notes. An excessive dose of green tea extract seems to be over 800 mg per day (or drinking 24 cups of green tea).

“It is also important to note that nutritional supplements sometimes contain unexpected ingredients which may also contribute to adverse health effects,” adds Downs. Reading labels carefully can help with this, but going back to the lack of FDA regulation, it’s also important to be judicious with which supplements you choose. Even more important? Working with your primary health care provider, who can not only tell you of any potential issues but also monitor how your supplements affect your body with blood work.

In my years of over-supplementing, I often couldn’t keep food down. Czerwony suggests that this might have been a symptom of my excessive consumption. “Most often, it’s going to be things like nausea or vomiting,” she explains. “Some people end up having diarrhea and headaches, and depending on whether they’re [taking] a fat-soluble vitamin, it could take some time to come on. It takes a little bit more time to accumulate in your system.” Gastrointestinal distress and headaches are the most common symptoms of chronic toxicity, but symptoms can vary from supplement to supplement.

And what if you take prescription medications? Our experts all agreed that there can be potentially catastrophic interactions. “St. John’s wort is known to interact with some of the enzymes in the liver, changing the concentration of many medicines in the body, so it should be used with great caution,” says Victor.

“St. John’s wort can also interact with other medications for depression, leading to a potentially life-threatening condition called serotonin toxicity,” adds Downs. Some symptoms of serotonin syndrome (or serotonin toxicity) include agitation, tachycardia and hallucinations.

Czerwony points out that St. John’s wort can also decrease the efficacy of antibiotics, a trait it shares with many other supplements, including magnesium, calcium, iron and vitamins A, C and D. And antibiotics aren’t the only medications that can be weakened with supplements. She also mentions that she’s seen cancer patients who try to power up their immunity with supplements, only to counteract the effects of their chemotherapy drugs.

Is there such a thing as safe supplement use? Yes, but it should take place under a doctor’s care. Here are some tips to do it safely:

Used correctly and under the oversight of a medical professional, nutritional supplements can be an integral enhancement to a balanced diet. For example, the depression that made my illness even more difficult to treat may have been improved with a safe, balanced vitamin D regimen. But taking more than 20 supplements a day was not the answer, especially when several of the ones I took likely lessened the efficacy of my antibiotic.

“Supplementation should never replace a healthy diet; it’s just to enhance it,” says Czerwony. “You should not feel like you can just eat whatever you want and then just take a bunch of supplements and think that you’re going to be OK.”

It’s all in the name—supplements are just that: something to supplement (or fill gaps) and build upon a healthy diet.

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