Could Low Testosterone Levels Be Involved in Alzheimer’s?

Like many other substances, testosterone exists in the serum in an available form (bioavailable, i.e. able to enter cells and react with other compounds) and in a ‘bound’ form, where it’s fastened, chemically, to a sex-hormone binding protein (a globulin) and is much more inert.  So when total serum testosterone is measured, it’s also important to know the level of bioavailable, or free testosterone.  Hong Kong researchers have reported a study of total and free testosterone levels in non-demented Chinese men over 55 in the Journal of Alzheimer’s Disease.    

Of the 153 men enrolled, 47 had mild cognitive impairment (MCI).  During the next year, 10 men were diagnosed with Alzheimer’s disease; all 10 were in the previously diagnosed MCI group, and all of them had low levels of free testosterone in their blood samples.  After making adjustments for age, education, BMI, fasting glucose level and serum high-density cholesterol levels, the researchers found that baseline bioavailable testosterone, presence of the ApoE4 genotype, and systolic blood pressure were all independent predictors of the development of Alzheimer’s.

A previous study in Caucasians, conducted in 2004, has shown a similar relationship between low free testosterone levels and an increased risk for Alzheimer’s.  Taken together, these two studies are sufficient to suggest a study of the use of testosterone to prevent Alzheimer’s.  However there’s not yet sufficient evidence to support the use of testosterone for this use, yet;  the hormone carries a small risk of increasing the likelihood of prostate cancer, so the risk/benefit for its use must be evaluated.

Another reason for caution is the frequent inaccuracy of testosterone testing.  A group of experts from the Endocrine Society has made recommendations concerning improving standardization of testing and appropriate education of healthcare providers.  So a waiting period might be appropriate before rushing to your doctor, requesting a testosterone test.