VOA标准英语2010年-Popular Supplement Fails to Lower Bloo（在线收听）

A new study of a popular dietary supplement indicates that, while pine bark extract is safe, it has no significant effect on blood pressure or other risk factors for heart disease. This new research seems to contradict evidence from earlier studies.

Previous research has shown an array of benefits from taking pine bark extract, ranging from reducing inflammation to treating skin disorders and menstrual symptoms. It is reported to have antioxidant properties and to help lower blood pressure, as well.

To test out some of the claims, Stanford University researcher Randall Stafford and colleagues recruited people who were overweight and had blood pressure slightly higher than normal — in other words, people likely to try a dietary supplement rather than expensive prescription drugs.

People in the study were randomly assigned to either take pine bark extract or a look-alike placebo.

After 12 weeks, the researchers found essentially no benefit from the supplement.

"We in fact found no difference between the pine bark extract group and the placebo group," said Stafford. "There were very small changes in blood pressure. And in fact, there was a slightly greater reduction in blood pressure among the placebo group, but it was a change that could have easily been explained by random chance."

Stafford says the results were surprising, because previous studies had shown some cardiovascular benefit. But he noted that there were problems with the methodology in the earlier studies, which were not placebo-controlled, double-blind trials like his was.

Also, products sold as "pine bark extract" can be made in a variety of ways and are not all the same, since these sorts of nutritional supplements are only loosely regulated, at least here in the U.S.

"There are a number of different pine bark extracts out on the market. They are extracted or derived in different ways. It is possible that other pine bark might have benefits where this one doesn't," he said.

In the United States and many other countries, government officials don't require natural dietary supplements to be proven safe and effective, the way other drugs are.

Stafford says his study illustrates how flimsy the scientific basis is for claims made by sellers of and advocates for many different supplements.

"Much of the expenditure on dietary supplements are for products that really don't have rigorous data supporting their use."

The study by Stanford researcher Randall Stafford and colleagues is published in the American Medical Association journal, Archives of Internal Medicine.