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Marek Doyle's avatar

I appreciate your commentary on many matters and it's clear to me that this is an important paper that shows the danger of black-and-white statement that 'estrogen replacement is good for the brain and reduces risk of Alzheimers'. However, I also think there is a danger in taking this study and forming another black-and-white conclusion that 'actually, estrogen encourages risk of Alzheimers and blocking estrogen reduces risk of Alzheimers'. To do so, we would have to ignore decades of research that supports estrogen's protective role here.

Instead, we should be asking, 'how is it that so many studies can find a protective effect of estrogen replacement on Alzheimers risk, yet estrogen blockers also show a protective effect?'. Even better, to consider what is the mechanism of estrogen / estrogen blockers and how might this explain this apparent contradiction? And does the specific population studied here provide us with clues?

To this end, I offer three statements (which I trust we can agree on) and two questions.

Statements:

- 1. estrogen has emphatically demonstrated neuroprotective effects in many types of research (through enhanced cerebral blood flow, neuroplasticity, and regulation of oxidative stress and excitotoxicity)

- 2. estrogen's effect on neuroinflammation is context-dependant (ie. some animal studies show that estrogen replacement increased susceptibility of senescent microglia to inflammation, it has been shown to reduced NkfB but enhance existing interferon signalling) and the literature indicates that it's more likely to exhibit pro-inflammatory activity in individuals with inflammatory/metabolic disorders.

- 3. this study is conducted on women who have been diagnosed with breast cancer (a condition that is, by definition, secondary to disturbed hormonal and immune activity).

Questions:

- 1. what if, like every other hormone in the body, that estrogen has both positive and negative effects, which may differ depending on the metabolic conditions of any given individual?

- 2. what if estrogen is protective in the population at large but, in certain groups that have already shown disturbed hormonal/immune activity, it increases risk?

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