The popular herbal supplement ginkgo biloba does not appear to prevent heart attacks and strokes in older adults, but may help lower their risk of blocked arteries in the legs, a new study suggests.

Ginkgo, one of the most widely used herbs in the U.S. and Europe, is often touted as a memory enhancer, but it is also being studied for its potential cardiovascular benefits.

The herb contains antioxidants called flavonoids, which may promote healthy blood vessel function; there is also evidence that ginkgo, similar to aspirin, prevents blood cells called platelets from clumping together to form clots.

For the current study, researchers randomly assigned more than 3,000 adults older than 75 to take either 120 milligrams of ginkgo or inactive placebo pills twice a day. They found that over the next six years, ginkgo users were no less likely to suffer a heart attack or stroke as those on the placebo.

The herbal group did, however, have a lower risk of developing peripheral artery disease (PAD), a buildup of artery-clogging plaques in the legs that reduces blood flow and can lead to pain and cramps when a person walks.

The finding is in line with past research showing that ginkgo supplements helped people with PAD walk farther without pain.

Still, it is too soon to recommend the herb for preventing PAD, the researchers report in the journal Circulation: Cardiovascular Quality and Outcomes.

Only 35 study participants developed PAD - 23 placebo users and 12 who were on ginkgo - and those numbers are too small to prove the herb made the difference.

“Clearly you can’t make a national recommendation based on these numbers,” lead researcher Dr. Lewis H. Kuller, of the University of Pittsburgh, said in a written statement, “but the data is intriguing.”

“Peripheral artery disease is a major public health problem and the preventive therapies are not very good,” Kuller added. “My feeling is that ginkgo and its class of agents, flavonoids, should be further evaluated to see if they have some benefit.”

Of the more than 3,000 men and women in the study, 164 suffered a heart attack over an average follow-up of six years, while 151 suffered a stroke and 207 developed angina - chest pain caused by reduced blood flow to the heart. There were no clear differences between the ginkgo and placebo groups in the risks of these problems.

The difference in rates of PAD - 0.8 percent in the ginkgo group and 1.5 percent in the placebo group - was significant in statistical terms.

It’s not clear why ginkgo might have an effect on PAD risk but none when it comes to heart attack or stroke. Larger studies are needed to see whether and why the herb may have unique effects on PAD, according to Kuller’s team.

Although ginkgo is available over-the-counter and generally considered safe, experts advise older adults to talk with their doctors before trying the herb.

Supplements can interact with each other or with any medication a person may be taking. With ginkgo, the primary concern is its potential to raise the risk of bleeding by interacting with drugs or supplements that “thin” the blood - including aspirin and other non- steroidal anti-inflammatory drugs, like ibuprofen and naproxen, as well as supplements like vitamin E and garlic.

SOURCE: Circulation: Cardiovascular Quality and Outcomes, online November 24, 2009.