The route of administration, timing, duration and dose of postmenopausal hormone therapy and cardiovascular outcomes in women: a systematic review.

BACKGROUND The effect of postmenopausal hormone therapy (HT) on cardiovascular disease (CVD) risk remains controversial. OBJECTIVE AND RATIONALE We aimed to systematically review the evidence regarding the role of dose, route of hormone administration, timing of initiation and duration of HT on cardiovascular risk among postmenopausal women. SEARCH METHODS The electronic databases Medline Ovid, Web of Science and Cochrane Central were systematically searched to identify studies published before 30 January 2018. Reference lists, using Elsevier's Scopus, of the included studies were searched for further identification of relevant studies. Clinical trials and observational studies that assessed clinical and subclinical cardiovascular outcomes in relation to dose, route of administration, duration of use, or timing of HT initiation among postmenopausal women were included. Data were extracted by independent reviewers using a pre-designed data collection form. The Cochrane Collaboration's tool and the Newcastle-Ottawa Scale were used by two independent investigators to assess the risk of bias in RCTs and in prospective observational studies, respectively. OUTCOMES In total, 33 unique studies (6 trials and 27 prospective observational studies) were identified, including a total of 2 588 327 women. The synthesis of the existing knowledge on this topic was challenging due to inconsistent findings between some studies, caused by substantial diversity in scientific rigor and quality across the available literature. Overall, the evidence did not support the concerns that oral or transdermal HT increases heart disease risk. Contrary, observational data showed that a beneficial cardioprotective effect can be observed even with use of low doses of oral HT (effect of 0.3 mg/day of oral conjugated equine estrogen was similar to that seen with the standard dose of 0.625 mg/day), but clinical trials to support a cardioprotective benefit of HT in primary prevention have not been identified. Furthermore, the current data suggested that oral and transdermal HT, in dose-dependent manner and irrespective of HT formulation, may increase thromboembolic risk, as well as risk of stroke. However, transdermal estrogen with <50 μg/day of estrogen combined with micronized progesterone appears to be the safer choice with respect to thrombotic and stroke risk. Also, vaginal HT administration may play a role in myocardial infarction and stroke risk prevention, but this is based on limited evidence and requires further investigation. The timing of HT initiation and duration may be important factors to consider when prescribing HT especially in women with adverse cardiometabolic profile and pre-existing conditions such as coronary/carotid atherosclerosis, which are at risk of developing, and thus progressing to CVD. The quality of evidence was generally low or moderate and the findings were based mostly on observational data. WIDER IMPLICATIONS Use of low-dose oral and transdermal HT appears to be safe with regard to CVD risk in women in menopausal transition and within the first years (e.g. 10 years) after menopause onset. In women with increased baseline thromboembolic risk, alternative non-hormonal medications are suggested as first-line treatment and transdermal estradiol alone or with micronized progesterone only should be considered when these options are not effective. When HT is initiated >10 years since the menopause onset (>60 years old), due to greater absolute risks of coronary heart disease, stroke and venous thromboembolism, HT should be used for the shortest time possible and in lowest possible dose and preferably transdermal administration should be recommended. However, an individualized treatment approach including baseline CVD risk assessment should be applied when prescribing HT. The majority of studies included in the current review are from North American and European populations, which might limit the generalizability of the findings of this review to the other populations. Finally, the quality of evidence included in this review was generally low or moderate, highlighting a need for more rigorous research to help us better understand HT and cardiovascular health.