Soy Supplement Doesn’t Ease Hot Flashes or Prevent Bone Loss

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When estrogen levels drop, either as a normal part of the aging process or because of breast cancer treatment, a woman is in menopause. Menopausal side effects can include hot flashes and night sweats. Over time, lower estrogen levels can weaken bones and may lead to osteoporosis.

For some women, hot flashes affect quality of life so much that they're considering medicine to ease them. Hormone replacement therapy (HRT) is one option. Still, there is strong evidence that HRT can substantially increase a woman's breast cancer risk and can increase the risk of breast cancer recurrence (the cancer coming back) or progressing in women already diagnosed with breast cancer.

So women and doctors have been looking for other ways to manage menopausal symptoms.

Soy foods have a lot of isoflavones, plant compounds that have a weak estrogen-like effect. Isoflavones are also called phytoestrogens. Because isoflavones are similar to estrogen, some doctors have thought that taking soy isoflavones might help ease hot flashes and help protect against bone loss after menopause.

But a study has found that taking isoflavone tablets every day for 2 years didn't help ease hot flashes or prevent bone loss. The research was published in the August 8-22, 2011 issue of the Archives of Internal Medicine.

The Soy Phytoestrogens As Replacement Estrogen (SPARE) study looked at 248 women between the ages of 45 and 60 who started menopause within 5 years of the study's start. Half the women took a tablet containing two different soy isoflavones (91 mg of genistein and 103 mg of daidzein) every day. The other women took a placebo (sugar pill) every day. The study was a double-blind study, which means that neither the women nor the doctors knew which women were taking the isoflavone tablets and which women were taking the placebo.

All the women in the SPARE study had a bone mineral density test to measure bone strength before starting to take either the isoflavone or placebo tablets. The women had another bone mineral density test 2 years after the study started. The researchers also recorded how many women were having hot flashes.

After 2 years, women who took the isoflavone tablets:

  • had about the same bone mineral density
  • were more likely to have hot flashes

compared to women who took the placebo tablets.

Nearly 50% of the women taking the isoflavone tablets reported bothersome hot flashes compared to 32% of the women taking the placebo.

About 34% of the women who took the placebo dropped out of the study compared to 19% of the women who took the isoflavone tablets. It's not clear why this happened, but it might have affected the results.

If you're having troubling hot flashes and other symptoms related to menopause, it's a good idea to ask your doctor about options to ease these side effects. You also might want to ask about steps you can take to help keep your bones as strong as possible after menopause. Some prescription medicines can help ease menopausal symptoms. Others can help reduce the risk of postmenopausal osteoporosis. There are also other lifestyle steps you can take to help ease hot flashes and boost bone health.

The Breastcancer.org All About Hot Flashes page has information on how to manage hot flashes.

The Breastcancer.org Ways to Keep Your Bones Strong page has information on medicines and other steps you can take to maintain the health of your bones.

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