Problems caused by dietary supplements are putting tens of thousands of Americans in hospital emergency rooms every year, a federal study finds.

Symptoms including rapid or irregular heartbeat or chest pains account for an estimated 23,000 ER visits annually, with more than 2,100 people requiring hospital admittance for treatment, the researchers report.

The true number of visits resulting from the use of supplements, including vitamins, minerals and herbal products, may be even higher as many patients do not inform ER doctors of their supplement use, authors of the study appearing in The New England Journal of Medicine say.

Exactly which supplements may create problems or why they do so is difficult to ascertain, the researchers say, because, unlike with prescription drugs or even over-the-counter medications, the Food and Drug Administration does not require supplement makers to prove the safety or effectiveness of their products before putting them on the market.

"We don't have information about what's contained in these products," says study leader Dr. Andrew Geller of the U.S. Centers for Disease Control and Prevention. "And often times multiple active ingredients are combined into a single product."

Significantly different active ingredients can also appear in similarly-named products, he adds.

"For all those reasons it can be hard for consumers, clinicians and public health agencies to determine which, if any, of the specific active ingredients caused the observed effects," Geller says.

A quarter of those ending up in emergency rooms because of supplement use are young adults between the ages of 20 and 35, the researchers say.

Other problems with the supplements include children ingesting supplements bought by an adult. With the exception of iron pills, there is no requirement for supplements to be marketed in child-resistant containers.

Another issue is with older patients, who sometimes have difficulty swallowing and who may choke on supplement pills, the study authors note.

The study used data collected between 2004 and 2013 from 63 hospital emergency rooms.

Americans spend nearly $14 billion a year on the increasingly-popular supplements, with 150 million using products claiming to treat a wide range of health conditions or promote weight loss.

What they don't realize, Geller says, is that the products can present a risk of serious side effects.

"Many Americans take dietary supplements in an effort to stay healthy, but these products can cause harm for some people," he says.