The estrogen-like compounds found in soy could help postmenopausal women get a better night's sleep, according to a small study.

These compounds, isoflavones, have been tested for a number of menopausal symptoms as well as for treating health problems that become more common after menopause, such as high cholesterol, high blood sugar, and increased body fat. But so far, results have been disappointing.

Insomnia is very common in older women, Dr. Helena Hachul of the Universidade Federal de Sao Paolo and her colleagues write in the journal Menopause. Studies of whether hormone therapy helps with sleep problems have had mixed results, they add.

To investigate whether isoflavones might be beneficial, Hachul and her team randomly assigned 38 postmenopausal women with insomnia to take either 80 milligrams of the isoflavones or a placebo for four months. All of the study participants underwent polysomnography, which involves spending the night in a sleep lab so vital signs, sleep stages, and movements can be monitored; this is considered the gold standard for measuring sleep quality.

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In the isoflavone group, average sleep efficiency (meaning the percentage of time that the women spent in bed that they were actually sleeping) went from 78 percent at the beginning of the study to 84 percent at the end; for the placebo group, sleep efficiency increased from 78 percent to 81 percent.

Among women given isoflavones, 90 percent reported "moderate or intense" insomnia at the beginning of the study, while 37 percent did after four months; in the placebo group, the percentages were 95 percent and 63 percent, respectively.

Between one-third and two-thirds of postmenopausal women have insomnia, Hachul and her colleagues note, but the causes underlying those sleep complaints may be varied. During the overnight observations at the beginning of the study, for instance, about a quarter of the women were found to be snorers, several had five or more sleep apnea events per hour, and a few displayed leg movements more than five times per hour.

Without knowing the source of postmenopausal insomnia, the researchers cannot say why soy seemed to alleviate it for many of the women taking the isoflavones.

In addition, because the study is small, the authors caution, it "does not permit the assumption that soy will act with the same efficacy for every woman." Nevertheless, they conclude, given that insomnia troubles so many women during menopause, "phytoestrogen treatment should be considered an option to improve patients' quality of life."