Biotin supplements, sometimes referred to as vitamin B7, have gained popularity with those seeking stronger, healthier hair, skin, and nails. But the Food and Drug Administration (FDA) recently warned that taking biotin supplements can alter results in a wide swath of medical tests, including ones for anemia, cancer, heart disease, pregnancy, and thyroid problems.

The agency said it has seen an uptick in the number of reported adverse events—including one death—related to the vitamin's interference with lab tests.

The FDA's warning shines a light on an issue that researchers have been flagging for years. Danni Li, Ph.D., director of clinical chemistry at the University of Minnesota Medical Center, released a study in 2009 that showed biotin supplements could interfere with the results of medical testing. Li has been in communication with the FDA ever since, urging the agency to warn the public. "The risks can be quite severe," she notes. "Depending on what kind of test, the consequences can even be deadly."

More on Dietary Supplements

The reason that taking biotin supplements could lead to misdiagnosis is because biotin is also used in medical tests to bond with proteins in blood. Those proteins are measured to detect many health conditions, according to the FDA. 

Lynn Burmeister, M.D., an endocrinologist at the University of Minnesota who has studied biotin’s effects with Li, says it can be difficult to be sure if a particular blood test could be skewed by biotin intake. For this reason, Burmeister suggests health providers ask patients whether they are taking biotin before administering any blood test.

This is also the advice from the Council for Responsible Nutrition (CRN), the largest trade group representing dietary supplements. CRN issued a statement in response to the FDA's warning, first clarifying that the FDA has not found health issues related to the biotin supplements themselves.

"The concerns raised by FDA are specifically directed to potential interference with certain lab tests," reads the statement from Duffy Mackay, N.D., CRN's senior vice president. According to CRN, "The simplest and most effective way to address these concerns is for healthcare practitioners to alert patients to temporarily stop taking their biotin supplements before getting blood work."

However, the FDA, in its statement, noted that there is not enough evidence to determine the length of time needed to clear biotin from the blood.

Why You Don't Need Biotin Supplements

Though people do need biotin (the Daily Value for adults is 300 micrograms), this vitamin can easily be found in many foods, such as egg yolks, fish, and nuts. But biotin supplements can contain 5,000 micrograms—about 16 times higher than the Daily Value—or more. And taking biotin supplements has not been proved to have measurable benefits. “There is virtually no evidence that biotin supplements actually work to improve skin, hair, or nails,” says Marvin M. Lipman, M.D., Consumer Reports’ chief medical adviser.

What's more, supplements in general are only loosely regulated. Though they fall under the purview of the FDA, the agency classifies them differently from drugs. The companies that make and sell them aren’t required to prove that they’re safe, that they work as advertised, or even that their packages contain what the labels say they do. "Supplement oversight is virtually nonexistent," Lipman says. This makes it difficult to even know how much you’re actually ingesting.

Consumers may not be aware of biotin's interference with blood tests, as supplement labels don’t carry such warnings.

“It’s great that the FDA posted a warning on its website, but most individual consumers aren’t going to see it there,” says Chuck Bell, programs director for Consumers Union, the policy and mobilization division of Consumer Reports. “Supplement manufacturers have an obligation to share this information through product labels or other means. You’ll have better healthcare outcomes if both consumers and providers are aware that medical tests could be affected by biotin use.”

“Everyone should tell their doctors about all the supplements they take, even if the doctor doesn’t ask,” advises Lipman. "If you use biotin supplements, stop taking them at least a week before having medical tests." And if you have had a test done and are concerned about the results, the FDA suggests you talk to your healthcare provider about the possibility of biotin interference. He or she can advise you on whether more testing should be done.