The Timing Hypothesis: Hormone Therapy for Treating Symptomatic Women During Menopause and Its Relationship to Cardiovascular Disease

The risks and benefits of menopausal hormonal therapy (HT) have been evaluated extensively over the past three decades. While the efficacy of HT for management of menopausal symptoms, including vasomotor symptoms and vaginal dryness is well established, its relationship to cardiovascular outcomes is complex. The timing hypothesis, which posits that the cardiovascular effects of HT depend on the timing of initiation of HT in relation to menopause, has helped shape our understanding of the cardiovascular outcomes related to HT. Based on results from female monkey studies, the timing hypothesis provides a framework to explain discrepancies in results between multiple observation studies and the Women's Health Initiative (WHI) hormone therapy trials. The WHI trials closed early in 2002 in part because of increased cardiovascular events seen in women on treatment. Subanalysis of the WHI results by age group, and more recent randomized control studies, including the Kronos Early Estrogen and Prevention Study (KEEPS) and Early Versus Late Intervention Trial (ELITE), demonstrate that the risk of adverse cardiovascular events for HT are low for women <60 years of age or within 10 year from menopause. Although current data does not support using HT for primary prevention of cardiovascular disease, it does suggest that HT can be safely used to treat symptoms in appropriately selected women close to menopause.

What the Women's Health Initiative has taught us about menopausal hormone therapy

Our understanding of the complex relationship between menopausal hormone therapy (MHT) and cardiovascular disease (CVD) risk has been informed by detailed analyses in the Women's Health Initiative (WHI), the largest randomized, placebo-controlled trial evaluating MHT in postmenopausal women. Although the WHI demonstrated increased risk of CVD events with MHT in the overall cohort, subsequent secondary analyses demonstrated that these risks were influenced by the woman's age and time since menopause, with lower absolute risks and hazard ratios for younger than older women. As MHT is the most effective treatment for the vasomotor symptoms of menopause, it is important to understand its risks and how to conduct risk stratification for symptomatic women. In addition to reviewing the WHI findings, studies pre- and post-WHI are reviewed to describe the relationship between MHT and CVD risk in menopausal women. The absolute risks of adverse cardiovascular events for MHT initiated in women close to menopause are low, and all-cause mortality effects are neutral or even favorable for younger menopausal women. The WHI has advanced and refined our understanding of the relationship between MHT and CVD risk. Although MHT should not be used for CVD prevention, absolute risks of CVD are low when MHT is started close to menopause in healthy women and hazard ratios tend to be lower for younger than older women. For women in early menopause and without contraindications to treatment, the benefits of MHT are likely to outweigh the risks when used for menopausal symptom management.