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 2>-hydroxyestrone/ 16>-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. (Authors abstract)

The transitional period often referred to as B menopause[ or climacteric  is a period of fluctuations, leading to decreased ovarian function. Increases in follicle stimulating hormone and luteinizing hormone, coupled with decreases in estradiol and progesterone, can give rise to a variety of uncomfortable symptoms, including urogenital problems (ie, vaginal dryness, urinary urgency), emotional shifts (eg, anxiety or feelings of depression), and vasomotor symptoms (hot flushes/flushes and night sweats). Hormone therapy
(HT) is regularly used for the short-term alleviation of menopausal symptoms. The use of phytoestrogen-rich plant food supplements as an alternative to HT for the management of menopausal symptoms and chronic diseases is of considerable interest, although results to date have been mixed. A meta-analysis of 28 interventions concluded that flax intervention significantly lowered total and low-density lipoprotein cholesterol in adults by 0.1 and 0.08 mmol/L, respectively, with postmenopausal women and participants with hypercholesterolemia gaining the most benefit. Although both whole flaxseed and isolated flax lignans were found to lower cholesterol, the high fiber content of flax may have contributed to this effect.20 Flax is also an excellent dietary source of >-linolenic acid (ALA),  which may also influence cardiovascular diseases through a wide range of activities.    There is little evidence to support flax consumption as influencing circulating sex hormone levels in postmenopausal women; generally, this also seems to be the case for premenopausal women.  However, flax intervention increased the length of the luteal phase (12.6 [0.4] d for flax vs 11.4 [0.4] d for controls), during which progesterone/estradiol ratios were significantly higher upon flax intervention compared with controls (but without significantly increasing progesterone levels). Flax consumption also resulted in minor increases in testosterone levels during the mid follicular phase. Similarly, daily consumption of 10 g of flaxseed for two menstrual cycles in 16 premenopausal women did not significantly change circulating levels of estradiol, dehydroepiandrosterone sulfate, estrone, progesterone, or serum sex hormoneYbinding globulin compared with controls.   Flax-mediated increases in the 2>-hydroxyestrone/16>-hydroxyestrone ratio represent a promising lead in breast cancer prevention research: hydroxyestrone metabolites should be prioritized as endpoints in future flax interventions in premenopausal and postmenopausal women.  The results assessed in this meta-analysis indicate that flaxseed is currently not indicated for the alleviation of vasomotor symptoms in postmenopausal women, and there is little evidence to support an effect on circulating sex hormones. A paucity of appropriate RCTs indicates that the effects of flax intervention on postmenopausal BMD are inconclusive. To date, there is little evidence to suggest a benefit for this area via biomarkers of bone remodeling. (Editors comments)