Objectives: The effect of testosterone (T) on sexual function in men is well established. However, less is known about its effects on cognitive function. The aim of this study is to investigate the relationship between T levels and sex-typed cognitive abilities in both eugonadal and hypogonadal men.
Design: A single-blind placebo-controlled design was employed in this study.
Methods: Thirty healthy eugonadal men and seven hypogonadal men participated in the study. Eugonadal men were randomised into one of two treatment regimens: (1) active group--receiving 200 mg of T enanthate i.m. weekly for 8 weeks (raising T levels into the supraphysiological range) or (2) placebo group--receiving 200 mg of sodium chloride i.m. weekly for 8 weeks. The hypogonadal group received the physiological replacement dose of 200 mg T enanthate i.m. bi-weekly for 8 weeks. All groups underwent a battery of neuropsychological tests and had circulating T measured at baseline, and at weeks 4 and 8 during treatment.
Results: A significant time by group interaction effect was found in the measure of spatial ability (i.e., block design test) indicating that the active group's performance declined significantly at week 4, compared to placebo group (F(4,64)=3.78, P<0.01). Conversely, the active group performed significantly better than the placebo group in the measure of verbal fluency (i.e., the Controlled Oral Word Association Test) at week 4 (F(4,64)=2.54, P<0.05). No significant changes were found on any of the other tests. Generally, the hypogonadal group performed less well than the eugonadal groups on all tests.
Conclusions: These results offer support to the notion that increased T has a differential effect on cognitive function, inhibiting spatial abilities while improving verbal fluency in eugonadal men.