The Alzheimer’s conversation in HRT has been almost entirely about estrogen for 20 years. A 2025 Nature study says that framing is only half the picture. The real driver is the ratio of estradiol to progesterone during perimenopause, and what happens to the brain when that ratio stays unbalanced for years.

In this episode, Nico Misleh, MSN, FNP-C walks through the full metabolic cascade the study identifies: estrogen receptor alpha destabilization, ERR alpha dysfunction, mitochondrial energy failure, glutamate excitotoxicity, and the on-ramp to neurodegeneration. He explains why unopposed estradiol can actually worsen the neuronal environment, why synthetic progestins like MPA do not deliver the same neuroprotection as bioidentical progesterone, and why perimenopause, not postmenopause, is the window that matters most.

If you prescribe HRT or are reconsidering whether to, this is the clearest mechanistic argument for treating progesterone as foundational rather than optional.

Link to the Study: pubmed.ncbi.nlm.nih.gov/41274899/ 

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