Brazil Study Finds Best Time for Hormone Therapy to Cut Disease Risk 60%

A new study presented at the 2025 Annual Meeting of The Menopause Society suggests that starting hormone therapy during perimenopause may offer substantial long-term health benefits. Researchers analyzed data from more than 120 million patient records and found that women who began estrogen therapy during perimenopause and continued it for at least ten years had about a 60% lower risk of developing breast cancer, heart attack, or stroke.

The study compared three groups of women. One group started estrogen therapy during perimenopause and continued for at least a decade before menopause. Another group began hormone therapy after menopause. The third group never used hormones. The researchers then tracked the occurrence of breast cancer, heart attack, and stroke over time.

Women who started therapy early showed roughly 60% lower odds of developing all three conditions. In contrast, women who began estrogen therapy after menopause showed only minimal protective effects. The study also found a slight increase in stroke risk, about 4.9% higher, for women who started therapy after menopause compared to those who never used hormones.

Estrogen plays a role beyond reproduction, affecting metabolic, cardiovascular, and cognitive health. When estrogen levels begin to fluctuate and decline during perimenopause, it impacts many body systems. In the heart, estrogen helps keep blood vessels flexible and supports healthy cholesterol levels. In the brain, it promotes neuroplasticity and supports serotonin and dopamine balance. In bones and muscles, it helps preserve density and strength, reducing the risk of osteoporosis and frailty later in life.

Introducing estrogen early, before these systems decline significantly, may help preserve their function. Waiting until after menopause, when estrogen receptors have been deprived of stimulation for years, may not deliver the same benefits and could pose more risk. This research adds to evidence that timing is a key factor in the effectiveness of hormone therapy.

Implications for women in their 30s and 40s

Women in their 30s or 40s who notice changes such as shorter cycles, sleep changes, mood fluctuations, or increased anxiety may want to discuss hormone therapy with a healthcare provider. Perimenopause can begin as early as the mid-to-late 30s. Tracking cycles, symptoms, and energy levels can help identify changes.

Finding a provider who is knowledgeable about menopause and hormone health is important. A clinician can personalize therapy based on symptoms, health history, and timing. Healthy lifestyle habits, including strength training, balanced nutrition, sleep optimization, and stress management, also play a role in supporting any hormone therapy plan.

This large-scale analysis reinforces the idea that the timing of hormone therapy may be critical. Starting estrogen during perimenopause may help protect the heart, brain, and bones for decades to come, in addition to managing current symptoms.