Updated on Oct. 21, 2024
Whether the pills interact with medications or the health claims don't hold up, these vitamins and other supplements are the ones experts say you're better off without.
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Around three-quarters of Americans use nutritional supplements—and 92% say they believe supplements are essential to maintaining their health, according to a 2023 Ipsos survey for the Council of Responsible Nutrition (CRN). But “Supplements are poorly regulated,” explains Julia Zumpano, RD, LD, a registered dietician with the Cleveland Clinic Center for Human Nutrition. “They may not be providing what they are stating they do unless they are third-party tested.”
It’s important to know that the US Food and Drug Administration (FDA) does not regulate supplements, which means many of these products haven’t undergone safety or efficacy studies. In fact, the FDA estimates there are between 50,000 to 80,000 adverse reactions to dietary supplements every year. And even when they’re safe, the supplements may not work as their marketing claims, they may be providing a form of a nutrient you cannot absorb, or you may be taking them incorrectly, which can affect absorption, Zumpano says. “You don’t need to be concerned with this when nutrients come from food.”
Nutrient-dense foods provide more benefits than individual supplements, too. Research published in the Annals of Internal Medicine found no advantage to taking dietary supplements and that when compared to nutrients in food form, nutrients found in supplements often don’t offer the same health effects.
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Aside from the risk of adverse reactions, it can sometimes be harmful to take supplements that you don’t actually need. “Not all supplements are water soluble,” explains Kendra Weekley, RDN, a registered dietician with the Cleveland Clinic for Human Nutrition. Water soluble means that it can dissolve in water, and therefore you can get rid of what you don’t use (typically in urine). “But there are some vitamins and minerals that you store and cannot get rid of the excess,” she says. “Too much of these vitamins and minerals can lead to toxicity—for example, vitamin A, vitamin E, vitamin D, and vitamin K are all stored in the fat and are not excreted when there is excess.”
Some vitamins and minerals also compete for absorption. “This means that the same cells can transport more than one micronutrient,” Weekley explains. For example, the same cell uptakes both copper and zinc. “So, if you are supplementing high-dose zinc for immunity or wound healing for an extended period of time, you are at risk for low copper levels.”
Lastly, “We need to remember where these vitamins and minerals are metabolized,” Weekley says. If you have renal or liver disease, it is important to check with your providers to see which supplements are safe to take. “Many herbs, vitamins, and minerals are broken down in the liver and filtered in the kidney, so if you have liver or renal disease, certain supplementation can cause damage to these organs.”
“Most supplements don’t have much scientific data or good quality data behind them,” Weekley says. This lack of safety and efficacy studies can, at worst, cause adverse reactions or, at best, have little to no beneficial effect—and at a high price point. “Sales [of supplements] increased by 50% between 2018 and 2020, with sales exceeding $220 billion in 2020,” she says. “People are spending a lot of money on supplements, which brings me back to my first point: Getting these micro and macro nutrients through food is the better and sometimes more affordable option.”
While nutritionists often encourage a food-first approach, there are times when supplementing is a great option. “For example, a person with low vitamin D on blood work should take a vitamin D supplement.” But, in general, nutritionists warn against overdoing it on certain supplements—and skipping others altogether.
“Iron is sometimes prescribed based on certain medical conditions, but use caution—it can have unpleasant side effects, including stomach upset and constipation,” says Ginger Hultin, MS, RDN, CSO, a Seattle-based registered dietitian nutritionist and adjunct faculty at the Bastyr University Center for Natural Health.
But taking iron supplements when you don’t need them can be harmful, too, according to the National Institutes of Health (NIH). High doses of iron supplements can cause abdominal pain, inflammation of the stomach lining, and ulcers—and it can also decrease your body’s zinc absorption. In some people, excess iron builds up in their bodies at toxic levels—an inherited condition called hemochromatosis—which can lead to serious organ damage.
“Take [iron] only if you to, and in the doses recommended by your doctor,” Hultin says. She suggests ensuring that you get the mineral from food, such as fortified breakfast cereal, oysters, beans, dark chocolate, tofu, lentils, spinach, meats like beef and chicken, and other sources of iron.
Biotin, one of the B complex vitamins, is essential for helping your nervous system function properly. But it’s often marketed as the miracle pill for long, healthy hair and nails—though there’s not much evidence that it works, Hultin says. “Unless there’s an outright deficiency, it’s not proven to help.” According to the NIH, biotin deficiency is rare—and it’s never been reported in healthy individuals eating a normal diet.
While there’s no evidence that high intake is toxic, the NIH says that excess biotin can interfere with laboratory test results, which can lead to misdiagnosis or improper treatment of a medical condition. Plus, this supplement can be filed under the “waste of money” category: Biotin is naturally found in a ton of different foods, from dairy and meat to sweet potatoes, bananas, oatmeal, and nuts.
Red yeast rice may effectively lower cholesterol levels, blood sugar levels, and blood pressure, according to the NIH. This is because as it is produced using fermentation, monacolin K is formed—a substance that’s structurally identical to lovastatin, a prescription statin medication used to treat high cholesterol.
Here’s the problem: The NIH says that there’s no way for consumers to know the amount of monacolin K in red yeast rice products. In a 2017 review of 28 popular brands published in the European Journal of Preventive Cardiology, the quantity of monacolin K ranged 60-fold across products (none of which included the quantity of monacolin K on the label).
What’s more: “[Red yeast rice] has side effects that should be monitored carefully by a physician,” Hultin says. “And because this is a supplement that acts in many ways like a medication, it would be very unsafe to take it at the same time as a cholesterol-lowering medication.”
Even though vitamin A is important for immune health and vision, deficiency is rare and typically associated with conditions including cystic fibrosis and gastrointestinal disorders, per the NIH. For most of us, however, vitamin A is readily available in many food sources, including fruits, vegetables, and many fortified foods, says Arielle Miller Levitan, MD, a board-certified internal medicine physician with Endeavor Health Medical Group and co-author of The Vitamin Solution: Two Doctors Clear the Confusion About Vitamins and Your Health.
Vitamin A supplements can spell trouble, too. “It is a fat-soluble vitamin, so even if you don’t take in too much, what you consume stays in your fat cells for a long time,” Dr. Levitan says. The NIH says that this accumulated vitamin A can cause severe headaches, blurred vision, nausea, muscle aches, and coordination problems. In chronic cases (someone takes too much vitamin A regularly), dry skin, joint pain, fatigue, depression, and abnormal liver test results can occur.
These heavy metals, often found in multivitamins, play important roles in different bodily functions. However, you need them in only trace amounts—which you likely obtain from food. “They do not leave your body easily, so a little goes a long way,” says Dr. Levitan. “Taking daily extra doses could potentially cause harm, as these metals can deposit in different parts of your body, such as your brain and bones. There has also been a question of the association of heavy metals with dementia.” Unless you have a proven, profound deficiency (often because of a chronic gastrointestinal illness), you should not take these on a daily basis.
When an immune-boosting nutrient is this easy to obtain through food, there’s simply no need to supplement. “Plus, our body does not store extra vitamin C,” says Jenn LaVardera, MS, RD, CDN, a registered dietician and the owner of Hamptons RD. “This means that when you go above and beyond your daily needs, your body simply eliminates the rest instead of saving it up for later.”
LaVardera warns that if you take megadoses over 2,000 mg, it can cause diarrhea, nausea, vomiting, headaches, and cramps. Most people easily meet their daily requirement—75 mg for women and 90 mg for men—which you can get from a cup of strawberries or broccoli (each providing about 80 mg).
“Supplements typically have one benefit marketed—for example, a multivitamin has vitamins and minerals,” Weekley says. Many multivitamin users believe the supplement helps prevent chronic disease, extends their lifespan, or makes up for a poor diet. Yet 2024 research published in JAMA discredits these claims, finding that multivitamin use is actually correlated with a slightly greater mortality risk.
While people who have digestive or malabsorption issues may need to supplement with a multivitamin, most of us are far better off prioritizing a healthy diet. “If you were to eat a variety of fruits and vegetables, you would get benefits like vitamins and minerals but also fiber, adaptogens, antioxidants, blood sugar control, and, of course, taste and the enjoyment of eating those foods,” Weekley explains. Some vitamins and minerals also compete for absorption in the body—so a multivitamin can work against itself.
In general, if you have poor nutrition, the best thing you can do is to work with a dietary expert to build an eating plan that works for you. And if you have a true nutrient deficiency—one that’s been diagnosed by a doctor through blood work—supplementing with that specific nutrient will be more beneficial than a multivitamin.
Vitamin D is essential for bone health, but low levels of vitamin D are also associated with an increased risk of cancer, heart disease, diabetes, autoimmune diseases, and depression, according to 2023 research from the National Library of Medicine. The NIH says that it can be difficult to get enough vitamin D from food alone—sunlight is our best source. And so people with limited sun exposure and people with darker skin are more likely to have inadequate vitamin D status.
Because it’s a fat-soluble vitamin, you should only take a vitamin D supplement if your blood work shows low or deficient levels. But if you do require a supplement, experts say to reach for D3, not D2. A 2024 review of research studies published in Advances in Nutrition explains that vitamin D3 is far more effective in raising blood serum levels compared to vitamin D2.
Whether you’re looking to boost your mood, reduce stress, improve your concentration, maximize memory, or balance your hormones, there’s an herbal or antioxidant product on the market for that. But Weekley says to exercise caution with these types of supplements. “‘Blends’ can often be problematic because it’s a common phrase where the company does not disclose what or how much of an ingredient is in their product.”
This is especially problematic because just because something is ‘herbal’ or ‘natural’ doesn’t mean it’s safe. Popular ingredients like ginger and curcumin can have blood-thinning properties and interact with medications, Weekley says. Germander (used in traditional medicine for conditions like diabetes, obesity, and hypertension) and kava (believed to help treat anxiety, insomnia, and stress) have been shown to cause liver damage. “Yohimbe [marketed as an aphrodisiac, weight-loss aid, and athletic performance booster] has been linked to changes in blood pressure and kidney damage.”
While trans fats are near-universally linked with negative health effects, one major study found an association between intake of cheese from grass-fed cows and a lower risk of heart attack, explains Gabrielle Gambino, MS, RD, CDN, CNSC, senior clinical nutritionist at NewYork-Presbyterian/Weill Cornell Medical Center. “CLA is found in cheese, and it is assumed that this trans fat may be part of the reason for some of the benefits reported in the literature.”
The exact mechanisms underlying any potential benefit of CLA are not well understood. But “The supplement industry has heard this message loud and clear and started producing CLA supplements,” Gambino says. “However, the supplement form of CLA may actually contain harmful man-made forms of trans fat, which may possibly negate any benefits the supplement may provide.”
Iodine is found in seafood, eggs, and dairy products—and in the US, the majority of table salt is fortified with iodine. But mild-to-moderate iodine deficiency is common and appears to be increasing, according to 2022 research published in Nutrients.
While iodine is a critical nutrient at all life stages, experts recommend taking iodine only under the guidance of your doctor because taking too much can have harmful effects on your thyroid, even causing hyperthyroidism. Some people may also experience adverse effects from iodine intakes that are considered safe for the general population, according to the NIH. Iodine supplements can interact with many types of medications as well, including blood pressure medications.
“Before taking any supplement, we need to know: Is it safe?” Weekley says. “The FDA does not regulate supplements closely, and consumers need to be informed about what they are buying and then ingesting.” She says to check if a supplement has been tested by a third party for its safety and efficacy, meaning that it actually contains what it says it does and has the effects it claims. “For example, Good Manufacturing Practice (GMP), National Sanitation Foundation (NSF), and US Pharmacopeia (USP) can help determine if the product is a safe choice.”
If you take any prescription medications, always check with your doctor or pharmacist about possible interactions before taking a new supplement, Zumpano says. More and more people are taking at least one prescription medication—from antibiotics to oral contraceptives to antihypertensives—and with the ongoing rise of supplement use, the overall risk of a potential interaction is around 49%, according to 2019 research published in Nutrients.
For example, vitamin K has properties that can make anti-clotting drugs like Warfarin less effective; St. John’s Wort is well known to interact with anti-depressant medications, and high doses of vitamin C and vitamin E might reduce the effectiveness of some types of cancer treatments, according to Weekley. Gingko, garlic, and calcium supplements are also common contributors to medication interactions, according to 2024 research published in The Permanente Journal.
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