Hormone Therapy and Effects on Sporadic Alzheimer's Disease in Postmenopausal Women: Importance of Nomenclature.

Numerous observational studies have suggested that hormone therapy (HT) might protect postmenopausal women against cognitive decline and Alzheimer's disease (AD). However, because of the significant disparity between results, especially those between observational and randomized controlled trials (RCT), this postulate remains unproven. A significant contributing factor to these inconsistencies is the loose use of the generic definitions of estrogens and progestogens with most studies not delineating the clear differences between non-endogenous and endogenously identical (bioidentical) hormones, their molecular binding affinities and actions, and resultant metabolites. This is highlighted by the generalized terminological use of HT, which is often used to encompass significantly disparate hormonal formulations without clear demarcation. This has impacted and continues to significantly influence interpretations of data, meta-analyses, observational studies, etc., relevant to AD. To progress forward and allow unbiased interpretation, it is no longer acceptable to group HT formulations together as a homogenous group. This will also allow differentiation between compounds that exhibit beneficial actions and those that do not and whether these effects are specific or generalized. The role of the endogenous hormones, 17 beta-oestradiol (E2) and progesterone (P4), in the development of sporadic AD in postmenopausal women is also examined.