The Hidden Risks of Dietary Supplements: Rising Cases of Liver and Kidney Damage Prompt Expert Warnings
Key Insights
A British consumer survey found that 76% of respondents regularly take at least one dietary supplement, with nearly one-fifth taking four or more daily.
Research indicates approximately 20% of drug-attributed liver injury (search) cases are actually linked to dietary supplements and medicinal herbs, with about 23,000 annual U.S. emergency room visits tied to supplement adverse effects.
Experts warn that "natural" does not mean safe, as substances like green tea extract, ashwagandha, vitamin A, and curcumin have been documented to cause liver and kidney damage (search), especially at high doses or with prolonged use.
The growing popularity of dietary supplements has sparked concern among hepatologists, gastroenterologists, and clinical dietitians worldwide, who report a troubling rise in cases of liver, kidney, and digestive system damage linked to products widely perceived as harmless. A survey by the British consumer organization Which? found that 76% of respondents regularly take at least one dietary supplement, and nearly one-fifth take four or more supplements every day—a trend experts say is increasingly landing patients in emergency rooms and hospitals.
Prof. Ziv Ben Ari, director of the Center of Excellence for Liver Medicine at Assuta, notes that the use of dietary supplements and medicinal herbs has expanded greatly in recent years. "Studies published in recent years indicate that about 20% of cases of liver injury (search) attributed to medications are actually linked to dietary supplements and medicinal herbs," she says. This figure aligns with research from the United States cited by gastroenterologist Dr. Pedro de Maria Pallares from the Hospital Universitario La Paz in Madrid, who told the BBC he is seeing increasing numbers of patients with liver problems caused by herbal supplements.
The Scale of the Problem
A landmark study published in 2015 in the New England Journal of Medicine, highlighted by clinical dietitian Michal Sukman of Maccabi Healthcare Services (search), found that in the United States alone, approximately 23,000 emergency room visits and 2,000 hospitalizations occur each year in connection with adverse effects from dietary supplements. The researchers found that weight-loss supplements, energy supplements, and performance-enhancing products were responsible for a large share of cases among young people, while among older adults, complications related to high-dose vitamins and minerals or errors in use stood out.
Sukman emphasizes that these findings do not necessarily show supplements have become more dangerous, but rather that more people are using them—often without professional guidance. "Many people start taking supplements after recommendations on social media, marketing campaigns or advice from friends, without checking whether they have a real need," she explains.
When 'Natural' Turns Toxic
One of the most pervasive misconceptions, experts warn, is that "natural" equates to "safe." A study published in 2024 in JAMA Network Open examined the use of herbal supplements in the United States and found that millions of people consume supplements with the potential to cause liver injury (search). Among the supplements that have appeared in medical reports are high-dose green tea extract, curcumin, ashwagandha, Garcinia cambogia, red yeast rice, and black cohosh.
The LiverTox scientific database of the U.S. National Institutes of Health (search) documents hundreds of cases of liver injury (search) linked to dietary supplements and medicinal herbs. Substances associated with liver damage, mainly in high doses or with prolonged use, include vitamin A, glutamine, ashwagandha, and green tea extract. The British Liver Trust, while noting limited data in the UK, says it is seeing cases of liver injury due to over-supplementation and urges people to consider "whether the potential benefits outweigh any possible risks."
The kidneys are equally vulnerable. Sukman notes that excessive intake of vitamin D over time may cause high calcium levels in the blood and kidney damage (search). High doses of certain minerals or uncontrolled consumption of protein supplements among people with existing kidney disease may also worsen their condition.
Regulatory Gaps and Contamination Risks
Prof. Ben Ari highlights a critical regulatory distinction: dietary supplements and medicinal herbs are not classified as medications but as food, meaning the oversight mechanism is fundamentally different. "Unlike medications, there is no requirement to prove their efficacy and safety through clinical trials before they are marketed, and responsibility for the product lies with the manufacturer," she explains.
This regulatory gap has real consequences. Studies examining the contents of dietary supplements and medicinal herbs have sometimes found substances not listed on the packaging. "Alongside vitamins, minerals and medicinal herbs, some products were also found to contain low doses of medications, such as steroids and painkillers, as well as various contaminants and toxins," Prof. Ben Ari says.
The Probiotic Puzzle
A new study published in Nature Microbiology raises further questions about probiotic supplements, among the most popular supplement categories globally. Researchers analyzed 352 over-the-counter probiotic products sold in the U.S. and found they contained a total of only 36 different bacterial species, with no consistency in composition among products marketed for the same health purposes. The researchers noted that scientific knowledge about the connection between many of these bacteria and the promised health effects remains limited, calling for the development of more evidence-based and targeted supplements.
Dangerous Combinations
Many consumers take multiple supplements simultaneously—a multivitamin, vitamin D, magnesium, omega-3, and an herbal supplement—without recognizing the potential for harm. Sukman warns that such combinations may lead to excessive intake of vitamins and minerals, interactions between different ingredients, strain on the liver and kidneys, cumulative side effects, and interactions with medications.
Specific examples include the risk of nerve damage from combining a multivitamin with a vitamin B6 supplement, impaired absorption when iron, calcium, and magnesium are taken together, and the accumulation of fat-soluble vitamins A, D, E, and K in the body over time. Interactions with prescription medications are also concerning: vitamin K may affect anticoagulant effectiveness, St. John's wort may reduce the efficacy of many medications, and ginkgo biloba, ginseng, and garlic may increase bleeding risk.
When Supplements Are Medically Justified
Despite the warnings, Sukman stresses that dietary supplements remain an important medical tool in specific situations: when a deficiency is confirmed by blood tests, during pregnancy or when planning a pregnancy, in restrictive diets such as veganism, in diseases that impair nutrient absorption, during drug treatment that affects absorption, after gastrointestinal surgery, or when there is a medical recommendation based on a specific health condition.
A review by the U.S. Preventive Services Task Force, published in 2022 in JAMA, found that for most of the healthy population, there is insufficient evidence that vitamin and mineral supplements reduce the risk of heart disease, cancer, or overall mortality. The researchers even recommended avoiding beta-carotene and vitamin E for the prevention of chronic diseases, due to a lack of benefit and concern about harm in some populations.
A Call for Evidence-Based Use
"A dietary supplement can be an effective and safe tool when it is given to the right person, at the right dose and for the right purpose," Sukman says. "But just as medication should not be taken without careful consideration, dietary supplements deserve the same approach: evidence-based, personalized and accompanied by professional guidance."
Prof. Ben Ari concludes: "Before starting to take a dietary supplement or medicinal herb, it is important to carefully weigh the benefit against the risk and the real need for using it. It is recommended to consult a family physician or dietitian before beginning use, and to avoid exceeding the recommended dose."
Blood tests, Sukman adds, are among the most important tools for tailoring supplements personally. "Instead of choosing a supplement based on an advertisement or a recommendation on social media, it is possible to check whether there is a real deficiency in iron, vitamin B12, vitamin D, folic acid or other components."