That's a real possibility, Karas said, but he also mentioned some possible physical mechanisms that might give HDL cholesterol anti-cancer activity.
"HDL alters the function of the immune system, which looks for abnormal cells that may be cancerous or precancerous and attacks them," he said. "It also has antioxidant properties, and there is a lot of interest in the role of antioxidants in reducing cancer risk."
HDL cholesterol also has anti-inflammatory activity, which might act against cancer, Karas said. His laboratory is "starting to think" about experiments to test these various theories, he said.
The only convincing proof would be a controlled trial testing whether medication that raises HDL levels reduces cancer incidence, Robinson said. No such medication is now on the market (other than niacin, which has a minor effect in raising HDL levels), although several are being tested for their effect on heart disease, stroke and other cardiovascular problems.
"We actually don't know that something is causing the disease unless we do controlled trials," she said.
The researchers who conduct those studies should monitor cancer incidence as well as cardiovascular disease among the participants, Karas said. The new study's finding that an appreciable effect on cancer was evident in just a few years "shows the importance in current studies to track cancer," he said. "Many don't."
Until the anti-cancer hypothesis is proved or disproved, Karas and Robinson said, the best thing to do is adopt the healthy lifestyle that can keep HDL cholesterol levels high -- exercising regularly, eating a healthy diet, not smoking and consuming alcohol in moderation.
To learn about HDL and LDL cholesterol and other blood fats, visit the American Heart Associa
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