Controlled flax interventions for the improvement of menopausal symptoms and postmenopausal bone health: a systematic review

Concerns regarding hormone therapy safety have led to interest in the use of phytoestrogens for a variety of menopause-related health complaints. Recent meta-analyses concerning soy and postmenopausal bone mineral density, flax and serum cholesterol indicate that significant benefits may be achieved in postmenopausal women. This study aimed to systematically review controlled flax interventions that had reported on menopausal symptoms and bone health in perimenopausal/postmenopausal women. A general search strategy was used to interrogate the Cochrane Library, Embase, MEDLINE, and SciFinder databases. Of 64 initial articles retrieved, we included 11 distinct interventions using flax without cotreatment. Interventions considering hot flush frequency/severity (five studies) and menopausal index scores (five studies) reported improvements from baseline with both flax and control treatments, with no significant difference between groups. There was little evidence to suggest that flax consumption alters circulating sex hormones, but flaxseed intervention increased the urinary 2α-hydroxyestrone/16α-hydroxyestrone ratio, which has been associated with a lower risk of breast cancer. Few studies considered bone mineral density (two studies) or markers of bone turnover (three studies). Flaxseed is currently not indicated for the alleviation of vasomotor symptoms in postmenopausal women. A paucity of appropriate randomized controlled trials means that the effects of flax intervention on postmenopausal bone mineral density are inconclusive.