Do the two most popular supplements for relieving hot flashes really work?

Women seeking to relieve their hot flashes and other symptoms of menopause with dietary supplements need to read labels carefully, especially on products manufactured from soybeans. That’s the finding of a recent chemical analysis of popular brands by, a private company that’s been assessing the quality of U.S. dietary supplements for more than 15 years.

Nearly all women report having hot flashes during menopause and for some women the flashes last for decades. But the most effective treatment is no longer routinely prescribed.

Estrogen not an option for many women

Estrogen pills cut hot flashes by 90 percent, but “a lot of women don’t want to take estrogen,” says says Mindy Kurzer, director of the Healthy Foods, Healthy Lives Institute at the University of Minnesota. And with good reason. In 2002, the Women’s Health Initiative study reported that women taking estrogen plus progestin for menopause had an increased risk of breast cancer, blood clots, stroke, and heart disease.

As a result, many women turn to more “natural” alternatives like dietary supplements.

Soy isoflavones

The most popular is isoflavones. These are estrogen-like substances in plants that sometimes boost—and sometimes counter—the effects of the estrogen that the body produces. The belief is that these plant estrogens help to make up for the decline in natural estrogen that occurs with menopause. The richest source of isoflavones are soybeans.

“It’s clear that soy and its isoflavones protect against hot flashes in women during menopause,” says the University of Maryland’s Chris D’Adamo.

Since 2000, 13 studies have given a daily isoflavone supplement or a placebo to a total of nearly 1,200 menopausal women in six countries. After periods ranging from six weeks to one year, those taking the isoflavones reported 21 percent fewer hot flashes. And in the nine studies that looked, hot flashes were less severe.

Not easy to pick out a good soy supplement

But women need to be aware of two big problems when buying an isoflavone supplement.

The studies that successfully reduced hot flashes usually tested at least 15 milligrams a day of a specific isoflavone called genistein. Those that weren’t successful generally tested less than 15 mg. (Genistein is the major isoflavone and makes up about half of the isoflavones in most soy foods.)

Unfortunately, isoflavone dietary supplements don’t disclose their genistein levels. And here’s maybe why: in their recent testing found that only three of six popular soy isoflavone dietary supplements contained at least 15 mg of genistein. In fact, one brand provided less than 2 mg per serving. So the chances of picking out a good soy isoflavone supplement to treat hot flashes may be no better than 50-50!

(We can’t tell you which brands passed and which didn’t. That information is available only to subscribers whose subscription fees help pay for the laboratory analyses of these supplements.)

Supplement manufacturers make it even harder to choose

And here’s a second hurdle women face: trying to figure out exactly how much isoflavones there are in a product.

Some isoflavones are bound to sugar and some – called the aglycone form – are not. The kind with sugar weighs more, the aglycone form weighs less. When researchers report that at least 15 mg of genistein may help relieve hot flashes, they’re referring to the aglycone form.

But some supplement manufacturers use the heavier isoflavone-with-sugar weights to list their isoflavone levels and don’t tell you that, which makes it look their products contain more of the active ingredient than they really do. Sneaky!

So it’s a double whammy for consumers. One, you don’t know how much genistein a product contains and, two, the isoflavone levels may be inflated. Good luck shopping!

Black cohosh

Another popular menopause supplement is black cohosh, which is prepared from the roots and underground stems of a plant native to North America. found that all five brands it tested contained the amounts of black cohosh listed on the labels. However, one contained significant amounts of lead. (The name of this brand is available to subscribers.)

But did these five brands contain enough black cohosh to help relieve hot flashes?

That’s impossible to say since researchers in the United States haven’t been able to show that black cohosh works at all, let alone how much would be needed of which component of the plant.

The black cohosh claims you see on bottles and in ads are based in large part on industry-funded, often inadequately-designed European studies. In the United States, four trials – none backed by industry – have tested black cohosh against a placebo in a total of more than 600 women. All four trials failed to show that black cohosh had any more benefit than a placebo.

For example, in one study of 351 women with hot flashes, which was funded by the National Institutes of Health, those assigned to take black cohosh for one year had no fewer or less severe hot flashes or other symptoms than similar women assigned to take a placebo.

“We believe black cohosh has no role to play in the treatment of hot flashes,” said the lead researcher in that study, Kate Newton of the Group Health Center for Health Studies in Seattle.

Sources: Menopause 13: 831, 2006; J. Clin. Oncol. 19: 2739, 2001; J. Clin. Oncol. 24: 2836, 2006; Ann. Intern. Med. 145: 869, 2006; Menopause 16: 1156, 2009.

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