The U.S. Food and Drug Administration announced on Monday that it was taking new steps to protect consumers from what dietary supplement providers claim their products are able to do - including preventing and curing the likes of Alzheimer's, diabetes and cancer.

The agency on Monday said it has sent 12 warning letters and five online advisory letters to various companies who it said claim their products can potentially do far more than they can actually do.

"Such claims can harm patients by discouraging them from seeking FDA-approved medical products that have been demonstrated to be safe and effective for these medical conditions," FDA Commissioner Scott Gottlieb said in a statement.

Indeed, dietary supplements can't claim to prevent, treat or cure diseases like Alzheimer's, Gottlieb said. Previous FDA action has targeted companies that have made similar false claims about their products helping patients with cancer and opioid addiction, Gottlieb said.

It is clear that "... the U.S. Food and Drug Administration plays an important role in helping consumers make use of safe, high-quality dietary supplements while also protecting Americans from the potential dangers of products that don't meet the agency's standards for marketing," he said.

Monday's crackdown comes as the FDA also announced it was starting what it called one the most sweeping modernizations of dietary supplement regulation and oversight in 25 years.