Detailed definition
The timing hypothesis emerged from re-analysis of the WHI data stratified by age and time-since-menopause, and from subsequent trials including KEEPS (Kronos Early Estrogen Prevention Study) and ELITE (Early versus Late Intervention Trial with Estradiol). These studies showed that women starting HRT before age 60 or within 10 years of the FMP had favorable cardiovascular outcomes (in some studies a possible reduction in coronary events, in others neutral) and favorable cognitive outcomes, in contrast to women starting HRT after age 60 or more than 10 years post-FMP, where benefits were diminished and some risks (notably stroke and cognitive decline in WHIMS) appeared. The proposed mechanism is that early-postmenopausal vascular endothelium is still healthy and responsive to estrogen's favorable effects, while later-postmenopausal vasculature with established atherosclerosis responds less favorably or unfavorably to estrogen.
Why it matters in menopause
The timing hypothesis is the single most important framework for interpreting HRT risk-benefit in 2026. It explains the apparent contradiction between the 2002 WHI headlines (older oral CEE+MPA in older women) and decades of observational data and modern trials in younger women. ClearedRx and other evidence-based menopause services use the timing hypothesis to guide treatment decisions.
Related terms
Sources
External references: Wikipedia.