Their new study also suggested that the pills, known as hawthorn or crataegus extract, may help to extend the lives of people suffering form heart failure -- at least in the short term.
But by two years, equal numbers of people given the supplement and placebo had died, says Christian J. F. Holubarsch, MD, of Median Kliniken Hospitals in Bad Krozingen, Germany.
"We can't yet say it saves lives," Holubarsch tells WebMD. "But the data are promising and are worthy of further study."
The study was presented at the annual meeting of the American College of Cardiology.
Hawthorn Extract Relieves Heart Failure Symptoms
Holubarsch says that extracts made from the leaves of hawthorn, a shrub commonly found in Europe, western Asia, North America, and North Africa, have been used for years to relieve minor heart failure symptoms such as breathlessness and fatigue.
The new study, he says, is the first to look at the effectiveness and safety of the extract when given to more severe heart failure patients.
Heart failure is a condition in which the heart can't pump blood effectively to the lungs or the rest of the body. This is usually because of damage to the heart muscle, such as damage from a previous heart attack.
The extract is a natural antioxidant that combats oxidative stress, a condition in which the body essentially has too many free radicals -- the waste products that result from all the chemical reactions occurring in the body.
Hawthorn Extract Extends Lives in Short Term
The study included 2,681 people with advanced heart failure who were taking standard drug therapy for the condition, including ACE inhibitors to lower blood pressure and beta-blockers to improve the heart's pumping abilities.
Half were given a hawthorn extract pill twice a day; the rest were given a placebo. Six months later, 5% of those on a placebo and 3% of those taking the supplements had died. This means that the risk of dying was 40% lower in those taking the extract, Holubarsch says.
Eighteen months later, 12% of patients on a placebo and 9.5% of those taking the supplements had died. This means that the risk of dying was 20% lower in those taking the extract, he says.
"On average, the extracts extended patients' lives by four months during the first 18 months of the study," Holubarsch says.
But by 24 months later, about 14% of people in both groups had died.
Hawthorn Extract Safe
Those taking the pills were less likely to suffer serious side effects such as fast orirregular heartbeats and chest pain than those on a placebo, he says. They were also less likely to suffer mild side effects like nausea and stomachaches.
Marc Pfeffer, MD, PhD, a heart specialist at Harvard Medical School, says these are important findings.
The study results should help alleviate concerns, as "we now know you can take this particular supplement safely with other heart medications," Pfeffer tells WebMD.