When it comes to supplements, there’s so much hype about their potential benefits that it can be hard to separate fact from fiction. While it’s true that vitamins and minerals are essential to health, it’s not true that taking them in pill, capsule, or powder form — especially in megadoses — is necessary or without risks.
For one thing, dietary supplements can sometimes interact with each other, as well as with over-the-counter (OTC) and prescription medication. In addition, unlike with drugs, the U.S. Food and Drug Administration (FDA) is not authorized to review dietary supplements for safety and effectiveness before they are marketed. It’s up to manufacturers to ensure that their products do not contain contaminants or impurities, are properly labeled, and contain what they claim. In other words, the regulation of dietary supplements is much less strict than it is for prescription or OTC drugs.
In March 2023, the FDA unveiled its new Dietary Supplement Ingredient Directory, a web page intended to help the public stay informed about the ingredients used in dietary supplements. Consumers can use the directory to look up ingredients used in products marketed as dietary supplements and find out what the FDA has said about that ingredient and whether the agency has taken any action pertaining to the ingredient.
According to the FDA, more than half of Americans take herbal or dietary supplements daily, with a report by Grandview Research noting the dietary supplements market was valued at $151.9 billion worldwide in 2021.
Used properly, some supplements may improve your health, but others can be ineffective or even harmful. For example, a systematic review published in the August 2019 Annals of Internal Medicine analyzed the potential effects of nutritional supplements on cardiovascular health, mainly heart attack and stroke, and found that few supplements help prevent heart disease — only omega-3 fatty acids and folic acid were effective. The same went for dietary changes, except for a low-salt diet.
Other research published the same year, involving self-reported dietary habits from a group of Americans, linked daily doses of more than 1,000 milligrams (mg) of calcium to a higher risk of death from cancer (though the National Cancer Institute notes that other studies suggest the opposite). Furthermore, the data showed that people who took in adequate amounts of magnesium, zinc, and vitamins A and K had a lower risk of death — but only if they got those nutrients from food rather than supplements.
“Buyer beware,” warns JoAnn Manson, DrPH, MPH, MD, the chief of the division of preventive medicine at Brigham and Women’s Hospital in Boston and a professor of epidemiology at the Harvard T.H. Chan School of Public Health in Cambridge, Massachusetts. “Many supplements on the market have not been rigorously tested. Very few supplements have been shown to be of benefit.” And, she says, many carry unsubstantiated health claims.
Confused? National Institutes of Health (NIH) fact sheets provide detailed information on the benefits and risks of individual vitamins and minerals, as well as herbal supplements. And if you’re managing an underlying health condition (especially if you’re taking medication) or are pregnant or breastfeeding, play it safe and have a conversation with your healthcare team before adding any new supplement to your regimen.
While supplement trends come and go, here are seven supplements that historically have been popular — and in all cases, experts recommend taking them carefully, if at all.
1. Vitamin D: Too Much Can Harm Your Kidneys
Vitamin D promotes calcium absorption in the body, and having enough is central to health and well-being, offering the promise of protecting bones and preventing bone diseases like osteoporosis, per the NIH. Supplemental vitamin D is popular because it’s difficult (if not impossible for some) to get enough from food.
Also, as the Centers for Disease Control and Prevention (CDC) notes, our bodies make vitamin D when bare skin is exposed to direct sunlight, but increased time spent indoors and widespread use of sunblock, as a necessary way to prevent skin aging and skin cancer, has minimized the amount of vitamin D many of us get from sun exposure.
But vitamin D supplements are a tricky topic. Sometimes, it can seem that guidelines and research contradict each other. The truth is, enthusiasm for vitamin D supplements is outpacing the evidence.
For example, when healthy pre- and post-menopausal women take vitamin D (up to 400 international units, or IU), it does not necessarily prevent them from breaking bones, according to a 2018 U.S. Preventive Services Task Force recommendation.
And high doses are not a good option. In healthy people, vitamin D blood levels higher than 100 nanograms per milliliter can trigger extra calcium absorption — and lead to muscle pain, mood disorders, abdominal pain, and kidney stones, notes the Cleveland Clinic. It may also raise the risk of heart attack and stroke.
“More is not necessarily better when it comes to micronutrient supplements,” says Dr. Manson.
That said, vitamin D supplements may benefit certain people, including those at risk of deficiency, such as individuals with darker skin, certain health conditions, and older adults, per MedlinePlus. The most recent American Geriatrics Society consensus statement specifically suggests that people older than 65 can help reduce the risk of fractures and falls by supplementing their diet with at least 1,000 IU of vitamin D per day, in addition to taking calcium supplements and eating vitamin D–rich foods.
Anyone can bolster their vitamin D levels by spending brief periods in the sun without sunblock — about 10 to 15 minutes a day, according to the NIH.
Keep in mind that vitamin D supplements and medications can interact with each other. Meds that don’t mix well with vitamin D include the weight loss drug orlistat (Xenical, Alli), various statins, such as atorvastatin (Lipitor), thiazide diuretics (such as Hygroton, Lozol, and Microzide), and corticosteroids like prednisone (Deltasone, Rayos, Sterapred), according to the NIH.
2. St. John’s Wort: Avoid Drug Interactions
St. John’s wort is a plant used as a tea or in capsules, with purported benefits for depression, attention-deficit hyperactivity disorder, menopause symptoms, insomnia, kidney and lung issues, obsessive-compulsive disorder, wound healing, and more, notes the NIH.
Small studies have shown St. John’s wort to be effective at treating mild depression. For example, a review of short-term studies looked at 27 clinical trials with about 3,800 patients and suggested that the herbal remedy worked as well as certain antidepressants at decreasing symptoms of mild to moderate depression.
But, says Denise Millstine, MD, an internist in the department of integrative medicine at Mayo Clinic in Phoenix, Arizona, “the biggest issue with St. John’s wort is its medication interactions.”
A study found that in 28 percent of cases when St. John’s wort was prescribed between 1993 and 2010, it was administered in dangerous combinations with antidepressant or anti-anxiety medication, statins, the blood-thinning drug warfarin (Coumadin), or oral contraceptives. For example, combining St. John’s wort with an antidepressant can cause serious complications, including a life-threatening increase in the brain chemical serotonin, according to the National Center for Complementary and Integrative Health.
St. John’s wort may also reduce the effectiveness of other medications, including birth control pills, chemotherapy, HIV or AIDS medication, and medicine to prevent organ rejection after a transplant, according to the NIH. Before you take St. John’s wort, read up on potential drug interactions and ask your doctor about the risks and benefits of this supplement, as well as how it compares to your other options.
3. Calcium: The Excess May Settle in Your Arteries
Calcium is essential for a strong skeleton, but as with all nutrients, too much of this mineral may be harmful. As the NIH notes, more than 2,500 mg per day for adults ages 19 to 50, and more than 2,000 mg per day for individuals 51 and over, can lead to problems.
With calcium supplements, hardened arteries, or atherosclerosis, and a higher risk of heart disease, are risks, though research is mixed, according to the Cleveland Clinic.
“Get calcium from your diet if you can,” advises Dr. Millstine, noting that research shows that calcium is better absorbed through food than through supplements. In a study, researchers analyzed a group of about 5,450 healthy adults’ calcium intake and screened their hearts for calcium deposits associated with atherosclerosis over 10 years. They found that people who got their calcium from food had a lower risk of atherosclerosis, while calcium supplements were associated with an increased risk of atherosclerosis.
The NIH recommends 1,000 mg of calcium a day for women ages 19 to 50 and 1,200 mg a day for women 51 and older. The recommendation for men ages 19 to 70 is 1,000 mg a day and 1,200 mg a day for men 71 and older. According to the Dietary Guidelines for Americans, there are various food sources of calcium, including plain low-fat yogurt, tofu, nonfat milk, cheese, and fortified cereal and juices.
Calcium deficiency, or hypocalcemia, may be detected by routine blood tests. If you have low calcium blood levels despite having adequate dietary intake, your doctor may prescribe a calcium supplement.
4. Multivitamins and Multiminerals: No Substitute for a Healthy Diet
Think that a healthy lifestyle requires not just good-for-you foods, exercise, and enough sleep but also taking a daily multivitamin-multimineral supplement? When you consider that an estimated one-third of adults in the United States and one-quarter of youths take them, per the NIH, you may be surprised to learn that the jury’s still out on whether they’re helpful.
One study published in the journal JAMA Internal Medicine, which examined data from nearly 40,000 women older than 19 who were part of the Iowa Women’s Health Study, found that, on average, women who took supplements had a higher risk of early death than women who didn’t take supplements. Multivitamins did little or nothing to protect against common cancers, cardiovascular disease, or death.
Other research has found benefits to taking multivitamins. For example, a study in the August 2017 Nutrients concluded that frequent use of multivitamin and mineral supplements helped prevent micronutrient shortfalls that might otherwise cause health problems.
Overall, research on whether multivitamins actually promote health is mixed.
For women of childbearing age, taking prenatal vitamins with folic acid is recommended by the American College of Obstetricians and Gynecologists to help prevent birth defects. Multivitamins might be prescribed by your doctor if you have malabsorption syndrome, a condition in which the body does not properly absorb vitamins and minerals.
In general, though, Manson says, “a supplement can never be a substitute for a healthy diet.”
Though multivitamins pose a low risk for drug interactions, the NIH recommends that smokers and former smokers avoid taking multivitamins with high levels of vitamin A or beta-carotene because these nutrients may increase the risk for lung cancer when consumed as supplements.
5. Fish Oil Supplements: Choose Fish or Flaxseed Instead
Rich in omega-3 fatty acids, fish oil has been touted as a means to reduce heart disease and other ailments. Yet increasing evidence suggests that fish oil supplements have questionable benefits.
For example, a study published in January 2019 in the New England Journal of Medicine found that omega-3 supplements did nothing to reduce heart attacks, strokes, or deaths from heart disease in middle-aged and older men and women without any known risk factors for cardiovascular disease. An earlier study analyzed people at high risk for cardiovascular disease and also reported no benefit.
Plus, a later review and meta-analysis of 83 randomized controlled trials, which was published in August 2019 in the journal BMJ, revealed that omega-3s, whether in supplement or food form, didn’t reduce type 2 diabetes risk among the 58,000 participants involved.
But it’s not all negative news when it comes to omega-3 supplements: A large randomized controlled trial published in January 2022 in BMJ suggests that fish oil supplements may provide health benefits when combined with vitamin D supplements, though in this case the benefits weren’t statistically significant. The authors observed that this cocktail, as well as vitamin D supplements alone, led to a lower incidence of autoimmune conditions such as psoriasis and rheumatoid arthritis.
Currently, there’s not enough positive evidence for doctors to prescribe fish oil supplements to every patient, though. Aside from the mixed research results, omega-3 deficiency is very rare in the United States, according to the NIH. One important drug interaction with omega-3 supplements is Coumadin (warfarin).
Still, many people fail to consume enough omega-3s in their diet for optimal health. Per the Harvard T.H. Chan School of Public Health, omega-3s play a critical role in the formation of hormones that relax artery walls, reduce inflammation, and aid blood clotting.
The best way to get adequate, and safe, amounts of omega-3s is by eating a variety of foods that are rich in them. The three main types of omega-3s are eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), and alpha-linolenic acid (ALA). According to the NIH, the following are some food sources of EPA, DHA, and ALA omega-3s.
EPA and DHA
- Fish and other seafood, especially cold-water fatty fish, such as salmon, mackerel, tuna, herring, and sardines
- Fortified foods, such as certain brands of eggs, yogurt, juices, milk, and soy beverages (may contain other forms of omega-3s, depending on the brand)
- Nuts and seeds, such as flaxseed, chia seeds, and walnuts
- Plant oils, such as flaxseed oil, soybean oil, and canola oil
6. Kava: Overuse Can Harm Your Liver
Kava is an herb that in concentrated forms has been used to treat general anxiety disorder with some success. A study suggests that the South Pacific plant can be an effective alternative treatment to prescription medication for people diagnosed with generalized anxiety disorder (GAD). An earlier, smaller study also showed that taking kava significantly reduced anxiety compared with a placebo in people with GAD.
But taking too much kava, or taking it for too long, has been linked to serious liver damage, including hepatitis, cirrhosis, and liver failure. As a result, according to the NIH, the FDA has warned that people, especially those with liver disease or liver problems, or those who are taking drugs that can affect the liver, should talk to their healthcare practitioner before using kava. In addition, the National Center for Complementary and Integrative Health reports that heavy consumption of kava has been associated with heart problems and eye irritation.
Several drugs may interact with kava, from anticonvulsants to anti-anxiety medications, and any drug metabolized by the liver, notes Mount Sinai. What’s more, people taking kava need to avoid drinking alcohol due to potential liver harm, the hospital recommends.
7. Soy Isolate: Careful With Estrogen?
Tofu, tempeh, and soy milk are all good plant-based sources of protein, fiber, and other key nutrients, per the Cleveland Clinic. Some women also take soy in supplement form because the plant contains estrogenlike compounds called isoflavones that are thought to relieve symptoms of menopause. Yet some health experts have raised concerns that the isoflavones in soy supplements may contribute to an increased risk of breast cancer.
The good news is that large-scale studies of humans have not shown any increased breast cancer risk from eating whole soy foods, such as tofu and edamame, in moderation, according to Cancer.Net.
Indeed, a study published in March 2017 in the journal Cancer looked at 6,235 breast cancer survivors and linked eating the equivalent of one serving of soybeans a week to a 21 percent lower risk of death from all causes during the nearly 10-year follow-up period.
But not enough research has been done on soy protein isolate (SPI) — the powder formed by removing the protein from the rest of the plant — to know its true effect on breast cancer risk, Millstine says. According to the Mayo Clinic, women with a family history of breast cancer or thyroid health problems may be more vulnerable to these effects. But again, this is theoretical and more studies are needed.
In addition to supplements, SPI is often found in power bars, veggie burgers, and some soups, sauces, smoothies, and breakfast cereals.
The bottom line: While current research suggests that whole-food sources of soy don’t increase breast cancer risk, the jury is still out. Before adding any supplement to your health and wellness regimen, discuss your options with your healthcare team and other health providers to weigh the potential risks and benefits for your individual situation.