Isoflavone phytoestrogen therapy has been proposed as a natural alternative to hormone replacement therapy (HRT), which has a beneficial effect on bone, but significant side effects.
The UK's medicines watchdog, the MHRA, recently advised women to stop taking the therapy for long-term periods. But while isoflavones have been widely studied for their effects on menopause symptoms such as hot flushes, there is less research into their effects on bone health.
A team of British scientists enrolled 205 women aged between 49 and 65-years-old in a a double-blind, randomized, placebo-controlled trial. One group received a daily supplement of red clover-derived isoflavone that included 26 mg biochanin A, 16 mg formononetin, 1 mg genistein, and 0.5 mg daidzein.
Bone density, body composition, bone turnover markers, and diet were measured at baseline and after 12 months.
Loss of lumbar spine bone mineral content and bone mineral density was significantly lower in the women taking the isoflavone supplement than in those taking the placebo, report the researchers in this month's American Journal of Clinical Nutrition (vol 79, no 2, 326-333).
However no such effects were seen on hip bone mineral content or bone mineral density, markers of bone resorption, or body composition. But bone formation markers (bone-specific alkaline phosphatase and N-propeptide of collagen type I) were significantly increased in the intervention group compared with placebo in postmenopausal women.
The researchers could only conclude 'a potentially protective effect' on the lumbar spine in women.
Chinese scientists reported last year that soy isoflavones have a mild, but significant, independent effect on the maintenance of hip bone mineral content in postmenopausal women with low initial bone mass.