Hoping to help consumers better understand dietary supplements, the government said Friday such products cannot legally claim to do such things as "prevent cancer" or "lower cholesterol."

Consumers buy some $5 billion worth of dietary supplements each year - pills, capsules and teas that are not approved by the Food and Drug Administration as safe and effective before they hit the market.Federal law allows the products to make truthful claims that they maintain the healthful "structure or function" of the body - but they may not claim to treat diseases. Actual treatments must undergo rigorous scientific study not required for supplements.

The question for dietary supplements was where to draw the line: Some companies argue, for example, that promising to lower cholesterol - or "maintain healthy cho-les-terol" - was not the same as claiming to treat heart disease, even though cholesterol levels are key to heart health.

Friday, the FDA proposed clearing the confusion by prohibiting supplements from even implying they can diagnose, treat, prevent or cure a disease or definitive disease symptom.

"Our hope is once this regulation goes final, the industry will see a safe harbor and have an incentive to stay within it," said FDA Deputy Commissioner William Schulz.

The rule would not let supplements claim to:

- Protect against the development of cancer, reduce the pain and stiffness of arthritis or lower cholesterol. Nor can they use such names as "Hepatacure," which implies it cures liver problems.

- Help the body respond to disease, by saying they "support the body's ability to resist infection or fight a virus."

- Substitute for a drug, through a name such as "Herbal Prozac" or claims that they contain aspirin or another well-known drug.

But supplement claims clearly targeted to help a well person stay well would be OK. The FDA said naming a supplement "Car-dio-health," for instance, is legal, as is saying it "supports the immune system," "reduces stress" or "helps maintain cardiovascular function."

Overall, the proposal "will be helpful," said Annette Dickinson of the Council for Responsible Nutrition, which represents supplement-makers.