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Women who consume higher levels of soy may have a lower risk of coronary heart disease, a new study suggests.
Researchers found that women in China with the highest levels of a soy compound called equol in their urine were 54 percent less likely to have heart disease, compared with the women in the study who had the lowest levels.
"Our results suggest that higher urinary equol excretion is related to a lower risk of coronary heart disease in women," said study author Dr. Xianglan Zhang, an assistant professor of medicine at Vanderbilt University Medical Center in Nashville, Tenn. "Our results provide some clues to further evaluate the role of soy in preventing heart disease," she said.
The study is the first to suggest that equol, a marker of soy food consumption as well as its absorption and metabolism in the body, may be linked with lower heart disease risk in women.
But the study did not show any connection between men's urinary equol levels and heart disease risk. Although the exact reasons are unclear, Zhang suspects that sex hormones, as well as dietary habits and lifestyle factors, may explain some of the differences in results between women and men.
The findings were published online Aug. 27 in the International Journal of Epidemiology.
Better clues to soy intake
The researchers reviewed data collected from middle-aged and older people in Shanghai. They compared the urine levels of compounds called isoflavonoids of 377 people who developed coronary heart disease, with 753 who did not.
Previous studies of soy and its effect on heart disease have relied on questionnaires, which require study volunteers to remember how often and how much soy they typically consumed. Urinary isoflavonoids levels may offer better clues to a person's true soy intake, the researchers said.
The findings were based on soy obtained from foods — such as tofu, soy milk and edamame— and do not apply to soy found in dietary supplements.
Scientists did not find any link between total urinary isoflavonoids levels and coronary heart disease. But when they looked at specific isoflavonoids, they found that higher equol levels were associated with a lower risk of coronary heart disease in women.
Equol is produced when soy is broken down by intestinal bacteria, and people vary greatly in their ability to produce it. Asian populations have been shown to have a higher percentage of equol producers than people living in the West. This is one reason, Zhang said, why more research is needed to evaluate whether soy consumption may protect against heart disease for women in Western countries.
As for why soy may protect against heart disease, Zhang suggests that it may help by lowering cholesterol and blood pressure, reducing inflammation, and improving blood vessel function.
Soy and the heart
"This is promising research that implicates a soy protein in cardiovascular prevention," said Dr. Nieca Goldberg, a cardiologist and medical director of the Joan Tisch Center for Women's Health at NYU Medical Center in New York City. But because the results were based on a small group of people in China, she said that more studies are needed to show if these same findings can be seen in other groups.
People in China have a higher intake of soy and isoflavones, compared with people in the United States, said Goldberg, a spokesperson for the American Heart Association.
She suggested that the study's take-home message is that we should add soy protein to the list of heart-healthy foods. Besides eating moderate amounts of soy foods, other heart-healthy food choices include whole grains and colorful fruits and vegetables.
Managing your weight, getting regular exercise, not smoking and reducing stress are also good strategies to help to protect against heart disease, she said.
Pass it on: Women who consume soy may have a lower risk of heart disease.