Declining Testosterone levels
Two papers that I came across recently that some guys over 30 might appreciate reading follow. I had trouble getting both down so that less than 10% of the text was here (so I would not be in breach of copyright). However, I think the important bits are still there. The papers say little more than I have loosely said in “My Pics” below, but carry a heap more authority.
Neurobiology of Aging 28 (2007): 914-920
Long-term measures of free testosterone predict regional cerebral blood flow patterns in elderly men
Scott D. Moffat, Susan M. Resnick
We previously reported that high circulating free testosterone (T) was associated with better performance on tests of memory, executive function, and spatial ability, and with a reduced risk for Alzheimer’s disease. In this study, we report that free T levels, measured on multiple occasions over 14 years, predict regional cerebral blood flow (rCBF) measured by PET in 40 older men… .These findings suggest that endogenous T influences brain physiology in regions critical for memory and attention and provide one mechanism through which T may affect cognitive function.
In men, total testosterone (T) levels decline by approximately 50% from ages 30-80  and as many as 68% of men over age 70 can be classified as hypogonadal based on their endogenous free T concentrations . This progressive loss of T with age in men has significant physiological consequences including decreased muscle mass, reduced bone density and sexual dysfunction . Among men with suspected andropause, memory loss was the third most commonly reported symptom after sexual dysfunction and general weakness . Despite the high morbidity associated with hypogonadism, there have been few studies specifically investigating the cognitive and neural effects of T supplementation in elderly men.
… . Although the effects of T on human brain and cognitive function are not clear, both associational [1,24] and randomized intervention trials [6,15] suggest that T may play an important role in the maintenance of cognitive function. In a series of studies [23-25], we have investigated the cognitive and neurological consequences of androgen depletion in elderly men. In one study, we followed 574 men for a mean duration of 19 years. We collected multiple serum samples for determination of total T, sex hormone binding globulin (SHBG), and a free T index, and prospectively evaluated presence or absence of a diagnosis of Alzheimer’s disease (AD). High free T levels were associated with a significantly reduced risk of AD … .
Journal of Clinical Endocrinology & Metabolism 88(7): 3064-3068
Testosterone Treatment Enhances Regional Brain Perfusion in Hypogonadal Men
Nasrin Azad, Shailesh Pitale, W. Earl Barnes, and Nicholas Friedman
The positive effect of testosterone replacement therapy on psychosocial well-being in hypogonadal men has been demonstrated by various psychometric tests. However, there is no report available that objectively demonstrates the effect of testosterone on the function of the central nervous system in men. In this report we studied cerebral perfusion in seven hypogonadal men on testosterone replacement therapy… .
The majority of hypogonadal men on testosterone replacement therapy report substantial improvement in mental and in overall well-being (1-4). The brain is recognized as a steroidogenic organ on the basis of its ability to produce and metabolize steroid hormones (5). Testosterone present in the brain, as in the other organs, can be either reduced to a more potent androgen, dihydrotestosterone, by 5a-reductase or aromatized to estradiol (6-9).
The presence of specific receptors for androgen and estrogen further supports the hypothesis that steroid hormones play an active role in neuronal functions (10-12). Furthermore, it has been demonstrated that steroid hormones promote neuronal cell growth and survival (13).
Steroid hormones may play a role as a neuromodulator. Studies have demonstrated that testosterone decreases |y-aminobutyric acid levels in hypothalamus (14,15). Testosterone and estradiol stimulate 5-hydroxytryptamine receptors and serotonin transporter protein metabolism in the central nervous system (CNS) (15-20).
In this study, we have tested the hypothesis that testosterone replacement therapy will increase CNS blood perfusion in hypogonadal men… . . The study demonstrates a novel finding that testosterone replacement therapy in hypogonadal men significantly increases cerebral perfusion in areas of the CNS, which are rich in serotonin and instrumental in memory and cognitive function.