Vitamin B7 has been called a “super vitamin” for its cosmetic and health effects, but a new University of Minnesota study and a federal advisory warn that it can throw off the results of important medical tests.

The U’s study compared the results of 23 immunoassay tests for six people before and after they consumed B7, or biotin. Nine of the tests were disrupted by the supplement.

Immunoassay tests help doctors determine if patients have had heart attacks, for example, or metabolic disorders. They reveal the amount of hormones and antigens in the body by triggering their immune responses and their measurable production of antibodies. Some of these tests contain elements of B7, because its acidity makes it useful for chemical analysis.

“It’s used in many lab tests and therefore it’s very concerning,” said Danni Li, director of clinical chemistry in the university’s pathology department, and a leader of the study.

Results were published in the Journal of the American Medical Association in September, after which Li received a call with questions from an official at the U.S. Food and Drug Administration. A warning about B7 and its impact on tests was released by the FDA in late November.

While Li’s comparative study was a first, case reports of B7 affecting test results have been published in medical literature for a decade.

Li said a test-related death spurred the FDA action. A patient who had been taking high levels of biotin died following a test that showed falsely low levels of troponin, a protein that is released when the heart has been damaged, according to an FDA advisory. That presumably led to incorrect decisions regarding the patient’s heart health.

B7 usage also interferes with thyroid tests, but Li said these discoveries shouldn’t necessarily dissuade people from taking the supplement. Some people take it for cosmetic reasons because it has been associated with shinier hair and stronger nails; celebrity Khloe Kardashian gave it a boost when she called it her “super vitamin” for these purposes. But Li said it also has been suggested as a treatment for a variety of diseases such as multiple sclerosis — though study results are limited.

Mostly, Li said, patients taking B7 should alert their doctors, especially if they are experiencing heart problems.

“In that urgent situation,” she said, “communication is definitely helpful and they can put less weight on that test.”

Some test versions are more sensitive to B7 consumption than others, Li’s research showed, so doctors can consider that when deciding which ones to use in their labs.