Relationship between testosterone, sex hormone binding globulin and plasma amyloid beta peptide 40 in older men with subjective memory loss or dementia

In a group of 28 older men with either subjective memory loss or dementia, serum total testosterone and sex hormone binding globulin (SHBG) correlated inversely with plasma levels of amyloid beta peptide 40 (Aβ40, r = -0.5, P = 0.01 and r = -0.4, P = 0.04, respectively). Calculated free testosterone was also inversely correlated (r = -0.4, P = 0.03), and all three relationships remained statistically significant after allowing for age. A similar but non-significant trend was seen with dehydroepiandrosterone sulphate (DHEAS), and neither luteinising hormone (LH) nor estradiol correlated with Aβ40. These data demonstrate that lower androgen levels are associated with increased plasma Aβ40 in older men with memory loss or dementia, suggesting that subclinical androgen deficiency enhances the expression of Alzheimer's disease-related peptides in vivo. An inverse correlation exists between SHBG and Aβ40, warranting further investigation.