The study was funded by the National Institutes of Health to determine if the widely popular product could preserve bone health and ease symptoms in the first years of menopause. The results show that, contrary to popular belief, soy isoflavone supplements neither prevent bone loss nor reduce menopausal symptoms.
The findings of the SPARE Study, which stands for Soy Phytoestrogens As Replacement Estrogen, were published in the August 8 issue of the Archives of Internal Medicine. Several major national media outlets, including The New York Times, The Wall Street Journal, CNN, the BBC and Reuters have reported the study results.
“The consumption of soy foods and soy supplements has dramatically increased in the last few years, particularly among women who start taking various over-the-counter products around the time of menopause, believing that these products will provide all the benefits and none of the risks of menopausal hormone therapy,” said Silvina Levis, M.D., professor of medicine, director of the Osteoporosis Center, principal investigator and lead author of the study. “Our study showed that soy phytoestrogen tablets do not provide any benefit, but fortunately do not cause any apparent harm either. The participants had the same rates of bone loss and menopausal symptoms, whether they were taking soy tablets or placebo tablets (sugar pills). The women on the soy tablets actually had more constipation and abdominal bloating.”
The participants, women aged 45 to 60 and within five years of menopause, were randomly assigned, in equal proportions, to receive either daily soy isoflavone tablets or the placebo and were not aware of which they were taking.
The women were followed for two years and underwent a bone density test (DXA) at the beginning and the end of the study to measure the rate of bone loss. The study showed no meaningful difference in the rate of bone loss between those taking the soy tablets and those taking the placebo. Additionally, those women taking the soy supplement reported no measurable improvement in the number or severity of menopausal symptoms such as hot flashes, or in vaginal cytology or cholesterol levels.
While the study is not an endorsement of hormone therapy, it objectively demonstrated that women who take soy isoflavone supplements will not enjoy any clinical benefits.