Eating flaxseed may not ease menopausal hot flashes after all, despite some promising early evidence that it might, according to a U.S. study.
Researchers at the Mayo Clinic in Rochester, Minnesota found that 188 women who were randomly assigned to eat a daily flaxseed bar saw no more improvement in their hot flashes than women given flax-free "placebo" bars.
Over six weeks, more than one-third of the women in each group had a 50 percent reduction in the frequency and severity of their hot flashes.
The similar results in both groups suggest a placebo effect or some other explanation for the changes some women reported, said researchers led by Debra Barton, whose findings were reported in the journal Menopause.
"What women should take from this study is that there is little compelling information to try flaxseed if the objective is to reduce hot flashes," Barton told Reuters Health in an email.
In an earlier pilot study, Barton and her colleagues had found that women who consumed flaxseed did see their hot flashes wane, on average.
But that study had no comparison group of women taking a placebo, she noted.
Flaxseed is high in compounds called lignans, a type of phytoestrogen. These are plant chemicals structurally similar to estrogen that may have a weak estrogen-like, and an anti-estrogen, effect on the body.
The most effective treatment for hot flashes is hormone replacement therapy, but since hormones have been linked to increased risks of heart disease, blood clots and breast cancer, many women want alternate remedies.
Some anti-depressants have been found to cool hot flashes by as much as 80 percent. But Burton noted that "natural" products, such as black cohosh, soy and now flaxseed, have failed to stand up to clinical trials.
The latest study included women with bothersome hot flashes, such as those occurring at least an average of four times a day. Half of them had a history of breast cancer, which would generally make it inadvisable to treat the symptoms with hormones.
Barton's team randomly assigned the women to eat either a flaxseed bar or a placebo bar each day for six weeks. The flaxseed bar contained fiber, protein and 410 milligrams of lignans. The placebo bar provided fiber and protein.
By the end of the study, 36 percent of women in both groups had a 50 percent drop in their hot flash "scores," which rank symptoms and severity. One third of women in each group said they thought their symptoms were moderately to "very much" improved.
Barton said there were several possible reasons.
In general, hot flash studies have found a significant placebo effect, with women feeling better because they expect to. Overall, 20 percent to 30 percent of placebo users improve, though some studies find even higher rates.
On top of that, hot flashes naturally cool off over time for some women, and they can be extremely variable since environmental triggers, such as hot weather or stress, often set them off.
"This is why it's important to perform randomized, placebo-controlled trials to understand the potential risks and benefits of interventions," she said.