Sixty-five studies were identified, of which there were 34 cohort studies (over 125,000 participants) and 24 case-control studies (over 8,000 cases) on primary prevention. In addition, there were 4 angiographic studies and 3 RCTs of secondary prevention, one of which reported the preliminary findings from the Women's Health Initiative study.
CVD mortality (8 studies): only current HRT use was associated with a reduced risk of CVD mortality. The summary RR was 0.64 (95% CI: 0.44, 0.93) for current HRT use and non significant (RR 0.75, 95% CI: 0.42, 1.23) for any HRT use.
CAD mortality (5 studies): only current HRT use was associated with a reduced risk of CAD mortality (RR 0.62, 95% CI: 0.40, 0.91). There was no association between past, ever or any use of HRT and CAD mortality ('any use' RR 0.74, 95% CI: 0.36, 1.45).
Stroke death (8 cohort studies): the summary RR for stroke death was 0.79 (95% CI: 0.60, 1.01) with any HRT use.
Incidence of CVD (4 studies): all measures of HRT use were associated with an increased risk of CVD incidence, although this was not statistically significant ('any use' RR 1.28, 95% CI: 0.86, 2.00).
Incidence of CAD: there was no association between 'any use' of HRT and the incidence of CAD (RR 0.87, 95% CI: 0.62, 1.21). There was also no association between HRT use and CAD events in those studies that adjusted for socioeconomic status or educational levels, but the summary RRs were reduced in those studies that did not adjust. The authors suggested that this indicates that socioeconomic status may significantly confound observations of reduced CAD amongst women using HRT.
Stroke: the summary RR showed an increased risk of stroke associated with 'ever use' of HRT (RR 1.12, 95% CI: 1.01, 1.23). There was an increased risk of ischaemic stroke with any HRT use (RR 1.20, 95% CI: 1.05, 1.40), but no significant effect on haemorrhagic stroke (RR 0.71, 95% CI: 0.25, 1.29). The preliminary results of the Women's Health Initiative trial indicated that HRT is associated with increased rates of stroke, myocardial infarction and blood clots.
Full details of all narrative discussions and other results were given in report.