Hormone Therapy Safe for Heart in Women Under 60 but Risky After 70

The Women's Health Initiative (WHI) trials originally reported that menopausal hormone therapy increased cardiovascular disease risk, triggering a dramatic decline in HRT use worldwide. But those findings pooled women across a wide age range — 50 to 79 years — obscuring whether younger women near menopause onset face the same risks as older women who begin hormone therapy decades after menopause. This secondary analysis, published in JAMA Internal Medicine, directly addresses that question by focusing on women with vasomotor symptoms (VMS) and stratifying results by age group.

The study analyzed data from both WHI hormone trials: one testing conjugated equine estrogens (CEE) 0.625 mg/day alone in women who had undergone hysterectomy (10,739 participants), and one testing CEE plus medroxyprogesterone acetate (MPA) 2.5 mg/day in women with an intact uterus (16,608 participants). Data spanned November 1993 to September 2012, with median follow-up of 7.2 years (CEE alone) and 5.6 years (CEE plus MPA). The primary outcome was atherosclerotic cardiovascular disease (ASCVD), a composite including nonfatal MI, hospitalization for angina, coronary revascularization, ischemic stroke, peripheral arterial disease, carotid artery disease, and CVD death.

Baseline moderate-to-severe VMS were present in 27.6% of the 50–59 age group and 8.7% of the 70–79 group in the CEE-alone trial, reflecting the natural decline in hot flash frequency with aging. Among women with VMS, 96.7% recalled symptoms near menopause onset, suggesting a genuine symptomatic population rather than incidental enrollment. CEE alone reduced VMS by 41% uniformly across all age groups (RR 0.59; 95% CI 0.53–0.66). In contrast, CEE plus MPA showed a striking age-related attenuation: VMS reduction was 59% in women aged 50–59 (RR 0.41), only 28% in those 60–69 (RR 0.72), and was essentially absent in women 70–79 (RR 1.20, CI 0.91–1.59; interaction P for trend <0.001).

For ASCVD outcomes, the age gradient was clinically dramatic. Women aged 50–59 with moderate-to-severe VMS showed no significant cardiovascular harm from either regimen: CEE alone HR 0.85 (95% CI 0.53–1.35) and CEE plus MPA HR 0.84 (95% CI 0.44–1.57). Women aged 60–69 showed a possible signal of increased risk with CEE alone (HR 1.31; 95% CI 0.90–1.90) but not with combined therapy (HR 0.84; 95% CI 0.51–1.39). The most alarming findings emerged in women aged 70–79: CEE alone produced an HR of 1.95 (95% CI 1.06–3.59), translating to 217 excess ASCVD events per 10,000 person-years; CEE plus MPA produced an HR of 3.22 (95% CI 1.36–7.63), corresponding to 382 excess events per 10,000 person-years (interaction P for trend 0.03 and 0.02, respectively).

These findings carry significant clinical implications. They provide the strongest randomized trial evidence that age at initiation — not just hormone type or uterine status — is the critical variable in HRT cardiovascular safety. Women aged 50–59 who have bothersome vasomotor symptoms can reasonably consider hormone therapy with a favorable risk-benefit profile. Women aged 60–69 should receive individualized counseling with acknowledgment of uncertainty. Women aged 70 and older with vasomotor symptoms should generally avoid hormone therapy due to substantially elevated cardiovascular risk, even though those symptoms are a recognized indication. Notably, this also challenges assumptions that persistent VMS at older ages necessarily justify treatment escalation.