The role of sex hormones in the prevention of cognitive decline is uncertain.
Some people say they have trouble remembering shopping lists, doing mental arithmetic, or finding the right word in conversation. Problems with memory and thought processes can be difficult to assess. The changes are subtle and are particularly difficult to pick up. Doctors call this mild cognitive impairment (MCI)
Resarch has shown that the female hormone oestrogen plays an important part in cognition in women. The role of testosterone in men for cognitive function is more uncertain.
Animal studies suggest mechanisms for sex hormones including testosterone to maintain optimal cognitive function. But, there are studies to suggest that endogenous testosterone levels are associated with aggression in men with cognitive impairment.
There is less research into how testosterone levels affect cognition in men. A review of studies in 2008 showed that some men having prostate cancer treatment to lower testosterone levels had cognitive impairment. Between about half (47%) and about two thirds (69%) of the men in these studies had these types of changes. The men showed difficulty in coping with problems that involved mentally rotating objects in space (spatial ability) and problems with multi tasking.
A pilot study on men in 2004 showed no significant changes in behavior, function, depression, or cognitive performance occurred following 12 weeks of testosterone replacement in men with low testosterone levels and early-to-moderate cognitive impairment.
Bottom line: It is uncertain if low testosterone levels in men affect their cognitive function.
Dr. Gudmundur Björnsson is an icelandic physician, a specialist in medical rehabilitation, a certified independent medical examineer (CIME) and an MBA. He now runs his own company as a medical advisor mostly in insurance medicine. He has previously been a head of a rehabilitation clinic and president IMA. 
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