The herb black cohosh may reduce hot flushes by acting on body temperature regulation, rather than through its oestrogen-like effects, report researchers, who suggest the finding increases the likelihood that the herb is a safe HRT alternative.
With recent news again pointing to adverse side effects, including breast cancer and stroke, for women on hormone replacement therapy, scientists are keen to find a safe alternative that can ease menopause symptoms. However questions have been raised about the efficacy of black cohosh, as well as other herbs such as red clover, promoted as HRT alternatives.
Until now, it was thought that black cohosh worked by targeting receptors for oestrogen. The new study finds for the first time that the herb targets serotonin receptors - some of the same receptors used by the brain to help regulate body temperature, according to a team of researchers from the University of Illinois at Chicago speaking at an American Chemical Society meeting yesterday.
"This study shows that black cohosh does not appear to be oestrogenic whatsoever and, as a result, is less likely to pose some of the dangers associated with traditional oestrogen replacement therapy," said study leader Judy L. Bolton, a professor at the university's College of Pharmacy. "We now have new clues to how it might work in the body."
Although preliminary evidence of the herb's efficacy in relieving hot flushes, night sweats and other symptoms of menopause is encouraging, further studies are still needed before it can be recommended, Bolton added, and there is still a lack of long-term safety data on black cohosh.
The researchers tested the effects of black cohosh on rats whose ovaries had been removed. The rats were divided into different groups and each group was fed a different concentration of cohosh extract daily for two weeks. Extracts of the herb, either alone or in combination with synthetic oestrogen, did not produce any changes in uterine weight or vaginal cell differentiation in the animals. This indicates that the herb has no oestrogenic effects, the researchers said.
In accompanying lab studies, the researchers showed that the black cohosh extract is capable of binding to human serotonin receptors, including those that help regulate body temperature. Previous studies have shown that these receptors may play a role in regulating hot flushes. Antidepressant medications, which some people believe may help reduce hot flushes, also bind to the same receptors. The current study may help provide an explanation for this effect, Bolton said.
However researchers still do not know the specific chemical or chemicals in black cohosh that target the serotonin receptors. Nor do they know if the herb may target hot flushes through additional mechanisms.
A Phase II clinical trial involving women with a high frequency of hot flushes is currently underway at the university to determine whether black cohosh actually reduces the frequency and intensity of hot flushes and other menopausal symptoms. The women will either receive black cohosh, red clover, a placebo or oestrogen replacement during the one-year NIH-funded trial, which is one of the largest and longest of its kind, according to Bolton.
Interest in black cohosh, which is indigenous to North America, soared after findings of the Women's Health Initiative study revealed last year that the health risks of oestrogen replacement therapy, including breast cancer and stroke, might outweigh its benefits for some women.
This study will also appear in the 10 September issue of the Journal of Agricultural and Food Chemistry.