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Federal officials are cracking down on supplement makers that claim that their products can treat Alzheimer’s and other diseases.

The Food and Drug Administration on Monday sent 12 warning letters and five online advisory letters to companies whose products are being “illegally marketed as unapproved new drugs” to prevent, treat or cure Alzheimer’s, diabetes and cancer.

“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,” said FDA Commissioner Scott Gottlieb in a statement.

“As the popularity of supplements has grown, so have the number of entities marketing potentially dangerous products or making unproven or misleading claims about the health benefits they may deliver.”

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Have you seen online ads for dietary supplements claiming to cure your #Alzheimers disease or memory loss? It’s a #healthfraud scam. There is currently no cure or treatment to stop or reverse the progression of #Alzheimers. LEARN MORE: https://t.co/llaycvlUWR pic.twitter.com/VqV0dvUGBx — U.S. FDA (@US_FDA) February 11, 2019

The warning letters, some written in partnership with the Federal Trade Commission, were sent to companies including Earth Turns, TEK Naturals, John Gray's Mars Venus, Blue Ridge Silver and Gold Crown Natural Products. The full list is available on the FDA's website. Products that were illegally marketed included green tea extract, fish oil supplements, bovine colostrum and melatonin.

Three-quarters of adult Americans and a third of children regularly take a dietary supplement, the agency noted. The industry is now worth more than $40 billion, producing up to 80,000 products, including pills, powders and liquids.

But 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.

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

"I've personally benefited from the use of dietary supplements and, as a physician, recognize the benefits of certain supplements," Gottlieb said. "Consumers need to have access to safe, well-manufactured, and appropriately labeled products."

As part of that goal, the agency is creating a new “rapid-response tool“ to let people know more quickly when a supplement ingredient is potentially dangerous. It is also is looking into ways of being better notified when the industry develops a new dietary ingredient and has created a Botanical Safety Consortium, which will look at better ways to test the safety of supplement ingredients.

The Council for Responsible Nutrition, the trade group for the supplement industry, praised the FDA's "enthusiasm for rooting out bad actors who put consumers at risk by spiking products with unapproved ingredients or drugs."

"We welcome additional enforcement actions to bring to justice those who would cynically trade on the halo effect of responsible industry to make a quick buck while ignoring the safety and health of consumers," Steve Mister, president and CEO of the council, said in a statement.