SAN FRANCISCO — Dozens of weight loss and immune system supplements are illegally labeled and lack scientific evidence to back up their health claims, government investigators warn in a review of the $20 billion supplement industry.
The report, released Wednesday by the Department of Health and Human Services’ inspector general, said 20 percent of 127 supplements investigators purchased online and in retail stores carried labels that made illegal claims.
In addition, many of those and other supplements lacked the scientific studies recommended to support their suggested uses.
Some labels went so far as to state the supplements could cure or prevent diabetes or cancer or help treat people with AIDS, claims strictly prohibited under federal law.
Consumers may not just be wasting money; they could be endangering their health, the report concluded.
‘‘Consumers rely on a supplement’s claims to determine whether the product will provide a desired effect, such as weight loss or immune support,’’ the report said. ‘‘Supplements that make disease claims could mislead consumers into using them as replacements for prescription drugs or other treatments for medical conditions, with potentially dangerous results.’’
The market for dietary supplements — from vitamin C tablets to capsules of echinacea — offers hundreds of products. The investigation focused on one segment that officials said is booming.
Federal law does not require supplements to go through rigorous testing to prove they are safe or even that they work. The Food and Drug Administration can act only after consumers get sick or a safety issue comes to light.
The inspector general found that, in numerous cases, when companies did submit evidence to back up health claims, it fell far short.
One company submitted a 30-year-old handwritten college term paper to substantiate its claim, while others included news releases, advertisements, and links to Wikipedia.
The report recommended that the FDA ramp up its oversight. It did not name brands or products or estimate the number of dietary supplements on the market.
The FDA said it would consider asking Congress for more oversight powers and agreed it should expand surveillance of the market.
Investigators also found that 7 percent of the weight loss and immune system supplements surveyed lacked the required disclaimer that the FDA has not reviewed whether the statement on the label was truthful.
Industry executives said the report highlighted a handful of bad actors.
‘‘This small sample of supplements shouldn’t smear the entire industry,’’ said John Shaw, executive director of the Natural Products Association.
‘‘Supplements are very, very safe compared to other products,’’ said Ashish Talati, a Chicago attorney whose firm represents supplement companies.