Avoid these supplements for better health

By Naveed Saleh, MD, MS
Published January 5, 2021

Key Takeaways

Dietary supplements are everywhere, with 73% of Americans taking them, according to a 2020 consumer survey on supplements, conducted by the Council for Responsible Nutrition (CRN). The data reveal that for the fourth consecutive year, approximately three-quarters of Americans report taking supplements. Despite a slight dip in 2019, this reflects an overall upward trend since 2015, when the percentage was 68%.

According to the survey, the most popular category is vitamins/minerals, taken by 98% of supplement users, followed by specialty supplements (46%); herbals/botanicals (44%); sports nutrition supplements (30%); and weight management aids (19%).  Along with its annual dietary supplements survey, CRN also conducted a COVID-19 survey in 2020 and found that two in five supplement users reported changing up their supplement routine since the start of the pandemic, with 91% of that subset reporting that they have increased their intake.

People take supplements to ensure that they are receiving enough essential nutrients or to enhance overall health and immune health status. Although some supplements have proven health benefits—for instance, calcium and vitamin D promote bone health, and vitamins C and E are antioxidants—no supplement can likely reverse chronic health conditions. Moreover, certain supplements have either no proven benefit or are downright dangerous

Here are five supplements that otherwise healthy people should avoid.

Vitamin K

Vitamin K plays an important role in blood coagulation and preventing excessive bleeding, but unlike many other vitamins, it is not usually taken as a dietary supplement. In fact, vitamin K deficiency is only a problem for a subset of the population, according to the Office of Dietary Supplements at the NIH. 

“Vitamin K deficiency is only considered clinically relevant when prothrombin time increases significantly due to a decrease in the prothrombin activity of blood,” advised the agency. “Thus, bleeding and hemorrhage are the classic signs of vitamin K deficiency, although these effects occur only in severe cases.” 

Of major concern, vitamin K supplementation can reverse the anticoagulant effects of warfarin, phenprocoumon, acenocoumarol, and tioclomarol. These anticoagulants work by depleting vitamin K-dependent clotting factors.


One of the world’s oldest living tree species, ginkgo has been used since ancient times in Chinese medicine to treat a variety of ailments, from asthma to kidney and bladder disorders. Today, the extract from ginkgo leaves is purported to help numerous conditions like dementia, anxiety, vertigo, eye problems, tinnitus, and more. But ginkgo likely has blood-thinning properties and potentiates anticoagulant agents such as warfarin, and may be unsafe during pregnancy, according to the NIH’s National Center for Complementary and Integrative Health (NCCIH), which advises caution in its use. 

The anticoagulative prowess of this supplement rivals that of streptokinase, according to one study, and its herbal extract can be used as a complement or substitute for this drug. 

However, in addition to possible health detriment, the NCCIH pointed out that taking ginkgo likely proffers little health benefit. With respect to dementia, anxiety, or peripheral artery disease, evidence on the efficacy of ginkgo is unreliable, inconclusive, or scant. 

“There’s no conclusive evidence that ginkgo is helpful for any health condition,” the agency wrote. “Although some studies suggest that ginkgo may help to slightly improve some symptoms of dementia, the findings have been described as unreliable. Also, other studies have had conflicting findings. Ginkgo neither helps prevent dementia or cognitive decline nor prevents Alzheimer’s-related dementia from getting worse.”

St. John’s Wort

This nutraceutical is touted to help with depression, although research on its efficacy is mixed, according to the NIH. In fact, any perceived benefit may be due to the placebo effect. 

Whereas any health benefit of St. John’s Wort is at best a matter of debate, this herbal extract does have many drawbacks. First, it can interact with birth control pills, antineoplastics, digoxin, HIV drugs, and antibiotics to make these drugs less effective.  It can also worsen the symptoms of bipolar disorder and psychosis, as well as result in serotonin syndrome when taken with serotonin-reuptake inhibitors.

Vitamin B12

This nutrient is necessary for red blood cell formation, neurological function, DNA synthesis, and many other important processes. It is typically obtained in the diet from fish, meat, and dairy products. Vitamin B12 deficiency is common, occurring in up to 15% of Americans, according to the Office of Dietary Supplements. However, most people who take vitamin B12 shots likely don’t need them, according to a Canadian study published in JAMA in 2019.

In the high-powered study, researchers mined a population-based retrospective cohort to ascertain the number of Ontarians with normal or undocumented B12 levels during the 12 months prior to initiating vitamin B12 injections. The investigators found that only 35.3% of the participants had marginally deficient vitamin B12 levels. Assuming a 64% inappropriate prescription rate, $45.6 million was wasted on inappropriate vitamin B12 shots.

Study authors not only questioned the actual need for vitamin B12 injections, but also the provider preference for the injections over oral B12 supplementation.

They wrote, “Most parenteral B12 in Ontario was prescribed to persons without evidence of deficiency in the year preceding their first B12 prescription. Potential drivers of this include patient demands and poor physician awareness of the evidence informing B12 supplementation."

They added, “It is also questionable whether parenteral supplementation is required over oral supplementation because oral B12 raises B12 serum levels and improves sequelae of deficiency as well as, if not better than, intramuscular B12, even for pernicious anemia. Plausible reasons why physicians prefer parenteral B12 include low quality of evidence supporting oral B12, society guidelines recommending intramuscular B12 for all patients, poor physician understanding of how to prescribe oral B12, and physician misperception that patients prefer parenteral over oral B12.”

Strict vegetarians and vegans are at greater risk for vitamin B12 deficiency because this nutrient is naturally found in animal products, according to the NIH. Fortified cereals and some nutritional yeast products contain B12, but further supplementation of this vitamin may be necessary for those who follow these diets—especially for pregnant or lactating women.


Iron is a mineral that helps in the formation of hemoglobin, and also supports muscle metabolism, healthy connective tissue, physical growth, neurological development, and other important bodily functions. Most Americans get enough iron in their diets, according to the NIH. Populations at risk of iron deficiency include infants, young children, teenage girls, pregnant women, and postmenopausal women. Overall, 14%-18% of Americans use supplements containing iron, with rates highest among lactating women (60%) and pregnant women (72%).

Other than bleeding during menstruation, the body has little outlet for excess iron, thus iron overload is a serious health concern.

“Adults with normal intestinal function have very little risk of iron overload from dietary sources of iron,” advised the NIH. “However, acute intakes of more than 20 mg/kg iron from supplements or medicines can lead to gastric upset, constipation, nausea, abdominal pain, vomiting, and faintness, especially if food is not taken at the same time. Taking supplements containing 25 mg elemental iron or more can also reduce zinc absorption and plasma zinc concentrations. In severe cases (eg, one-time ingestions of 60 mg/kg), overdoses of iron can lead to multisystem organ failure, coma, convulsions, and even death.”

Share with emailShare to FacebookShare to LinkedInShare to Twitter