Study designs of evaluations included in the review
Controlled studies were eligible for inclusion. All of the included studies were randomised controlled trials (RCTs); some were parallel-group and others were crossover RCTs.
Specific interventions included in the review
Studies that compared soy-derived semipurified isoflavone extracts used as dietary supplements with placebo or control were eligible for inclusion. The studies had to use isoflavone alone and not in combination with other herbal extracts. Studies that evaluated dietary soy sources of isoflavone or red clover isoflavone extracts were excluded. The total aglycone isoflavone dose evaluated in the included studies ranged from 30 to 114 mg/day. In the review, studies were classified as low-genistein-containing (less than 15 mg genistein per treatment; actual range: 5 to 9 mg) and high-genistein-containing (at least 15 mg genistein per treatment; actual range: 15 to 75 mg) soy isoflavone supplements. The overall, average total isoflavone treatments for the low and high genistein groups were 56.8 mg and 64.8 mg, respectively. The duration of the included studies ranged from 6 to 52 weeks, with most studies ranging from 12 to 24 weeks.
Participants included in the review
Studies of otherwise healthy women receiving treatment for hot flashes (either alone or in combination with other menopausal symptoms) in the early postmenopausal period were eligible for inclusion. Studies of women with a surgically induced menopause or cancer patients currently receiving oestrogen-like treatments were excluded. All of the included studies defined postmenopausal status as the absence of menses for at least 6 months. The mean age of the participants was 52.2 years and the mean number of hot flashes per day was reported to range from 4 to 10 (based on 8 studies).
Outcomes assessed in the review
Inclusion criteria were not specified in terms of the outcomes. The primary review outcome was the reduction in hot flash occurrence. Three studies that used a menopausal index to measure overall menopausal symptoms but did not apparently report the occurrence of hot flashes were also included.
How were decisions on the relevance of primary studies made?
The authors did not state how the papers were selected for the review, or how many reviewers performed the selection.