Study finds soy could be good for heart, bones of premenopausal women

New research suggests that a diet high in soy could be good for the hearts and bones of premenopausal women. The findings from two separate studies conducted at Wake Forest University Baptist Medical Center were reported at the annual meeting of the North American Menopause Society in Washington, D.C.

The results suggest that for cholesterol and bone density, the natural plant estrogens in soy may be most effective in conjunction with the body’s own estrogen -- which would make it especially potent in women who haven’t reached menopause. They also point to the possibility the estrogen-soy synergy could have other benefits as well.

In one study, Jay Kaplan, Ph.D., found that monkeys fed a soy-based diet had improved cholesterol levels compared to monkeys who ate a diet of milk and animal protein. The improvement was most pronounced in monkeys who were at highest risk for heart vessel disease.

The researchers measured the ratio of total cholesterol to HDL (high-density lipoprotein) or “good” cholesterol. A lower ratio is considered healthier. In monkeys who were at highest risk for heart disease, the cholesterol ratio decreased by 48 percent compared to the monkeys who didn’t eat soy. The lower-risk monkeys that consumed soy had a 33 percent decrease.

Kaplan said a 48 percent drop in the cholesterol ratio would likely equate to a 50 percent reduction in the size of fatty deposits in the arteries, which can cause heart attacks and strokes.

The monkeys deemed at highest risk for heart disease were those with impaired ovarian function because they are the low-status or “subordinate” animals in their group. Monkeys naturally form social hierarchies when they live in groups. In previous research, Kaplan found that the stress of being subordinate impairs ovarian function, which means that lower levels of estrogen are produced. In both monkeys and people, reduced levels of estrogen are associated with increased risk for heart vessel disease.

Kaplan had already shown that providing additional estrogen in the form of birth control pills was effective at reducing atherosclerosis in subordinate monkeys. The current study was to see if soy can serve as a natural alternative to estrogen.

Kaplan said the work could be important to women in several ways.

“Studies have shown that heart vessel disease, or atherosclerosis, begins in the 30s and 40s in women,” said Kaplan. “From our work in monkeys, we believe that the time to prevent cardiovascular disease in women is before menopause, not after. Soy seems to provide a potent protection in monkeys, in terms of cholesterol levels, which is a good marker for general cardiovascular risk. We presume the benefit would apply to premenopausal women as well.”

In the second study, Cynthia Lees, D.V.M., Ph.D., found that monkeys that consumed soy had an increase in bone mass over the monkeys that didn’t consume soy.

“The increase was small, but this is an exciting finding,” said Lees, an assistant professor of comparative medicine. “Previous studies in postmenopausal monkeys and women found either no increase or bone loss.”

The study raises the question of whether exposure to soy before menopause could help maintain bone mass after menopause. The loss of bone mass that occurs naturally after menopause can lead to osteoporosis and an increased risk of fractures.

Lees said that Japanese women, who consume a diet high in soy throughout life, seem to preserve bone mass better than American women.

“This suggests the possibility that if women consumed soy on a regular basis before menopause, it could benefit their health after menopause,” said Lees.

Kaplan said that because the soy-estrogen combination resulted in improvements in both cholesterol and bone, it might also positively affect others areas of the body that estrogen targets, including the brain and arteries.

For both studies, the monkeys were selected to represent women in their 30s and 40s. Half of the monkeys consumed soy with isoflavone levels equal to human intake of about 129 milligrams a day. These levels of isoflavones, which are the plant estrogens in soy, are about two times higher than amounts consumed by many Asians, who typically eat more soy than other populations.

The researchers hope to study whether lower levels of isoflavones, consumed over a longer period of time, would be as effective as the high levels that were taken for 12 months in this study.

SOURCE: Wake Forest University Baptist Medical Center, October 1, 2004