Relationship between testosterone supplementation and insulin-like growth factor-I levels and cognition in healthy older men

Abstract

Background. Our laboratory has previously reported that testosterone (T) administration to older men significantly improves cognitive function. This study examined potential changes in insulin-like growth factor (IGF) IGF-I, IGF-II and IGF-related binding proteins in response to T administration in older men and their relationship to cognitive functioning.Methods. Twenty-five healthy community dwelling volunteers, ranging in age from 50-80 years were randomized to receive weekly intra-muscular (i.m.) injections of either 100 mg T enanthate or placebo (saline) for 6 weeks. Serum hormone levels and cognitive functioning was assessed at baseline and twice during treatment.Results. Significant positive associations between IGF-I and IGF-II and spatial memory, spatial reasoning, and verbal fluency were observed after 6 weeks of T administration. Increased serum T levels from treatment were positively associated with improvement in spa- * Corresponding author. tial reasoning performance, whereas estradiol was associated with a decline in divided attention performance. Serum IGF-I, IGF-II and IGFBPs did not change in response to T treatment. Conclusions. Our results suggest that T, estradiol and IGF-I may have independent and selective effects on cognitive functioning. Positive associations between T levels and cognition are consistent with an effect of androgen treatment, whereas positive associations between IGF-I levels and cognition are reflective of a relationship between endogenous IGF-I levels and cognition. 

Growth Hormone Deficiency and Memory Functioning in Adults Visualized by Functional Magnetic Resonance Imaging

“…It is known that the number of GH receptors in the brain of rats declines with aging [37] and that IGF-1 potentiates acetylcholine release from the hippocampus. With aging there is a dramatic reduction of IGF-1 protein levels and receptor density in this structure [38, 39]. Changes in the cerebrospinal fluid concentration of the dopamine metabolite homovanillic acid are shown after GH treatment [4, 5, 40].…”

Stress hormones, sleep deprivation and cognition in older adults

“…These studies showed significantly improved memory [62,64] and visuo-spatial function [62,63] in testosterone compared to placebo groups.…”

The relation between insulin-like growth factor I levels and cognition in healthy elderly: A meta-analysis

“…Twenty-five healthy volunteers (age 50-80) received weekly intra-muscular injections with either 100 mg testosterone or placebo for 6 weeks [23]. Serum IGF-I levels did not change in response to the testosterone treatment.…”