Sex hormone-binding globulin (SHBG), which regulates androgen and estrogen bioavailability, has been linked to cognitive decline, but its relationship with temporal lobe changes-an area vulnerable in Show more
Sex hormone-binding globulin (SHBG), which regulates androgen and estrogen bioavailability, has been linked to cognitive decline, but its relationship with temporal lobe changes-an area vulnerable in early Alzheimer's disease (AD)-remains unclear. This study aimed to investigate whether plasma SHBG levels are associated with temporal lobe volume and cognitive performance across the cognitive spectrum from normal aging to AD. Participants included individuals with AD (n = 85), mild cognitive impairment (MCI; n = 304), and cognitively normal controls (CN; n = 50). Cognitive performance was assessed using the ADAS-Cog 11, MMSE, and CDR-SB. Temporal lobe volumes were derived from MRI scans using tensor-based morphometry (TBM), and plasma SHBG levels were measured using a validated immunoassay. Multiple regression analyses adjusted for age, sex, education, handedness, and APOE ε4 status were conducted, followed by mediation analysis to test indirect effects through temporal lobe volume. After covariate adjustment, elevated plasma SHBG levels were significantly associated with reduced temporal lobe volume in the MCI group. Across both MCI and AD participants, greater temporal lobe volume correlated with better cognitive performance on all tests. Mediation analysis indicated that in MCI, the relationship between higher plasma SHBG and poorer cognitive outcomes was significantly mediated by reduced temporal lobe volume. These findings suggest that elevated SHBG may contribute to early cognitive impairment in MCI through its impact on temporal lobe integrity, highlighting SHBG as a potential target in the prodromal stages of AD. Show less