Cognitive functions and sex steroids.

In humans, levels of adrenal (DHEA(S)) and gonadal (estradiol, testosterone) sex steroids decline with age. Studies in rodents have demonstrated that these hormones can have neuro-excitatory and neuro-protective effects in the central nervous system (CNS). Behavioural studies repeatedly have reported enhanced memory performance of rats and mice after acute or sub-chronic treatment with sex steroids. The current review summarizes human studies on this topic conducted by the author as well as other groups. Epidemiological as well as experimental studies have in general shown that estradiol replacement improves cognition, especially verbal memory in menopausal women. Similarly positive effects of testosterone replacement in older men have been reported in several, but not all studies. Cognition enhancing effects of DHEA replacement in older healthy humans in contrast could not be demonstrated with short (weeks) or prolonged (months) treatment regimes. Even though most results support the notion that estradiol in women and testosterone in men can enhance cognition in older healthy humans, more research is needed before recommendations for the clinical practice can be made.