Age-sensitive cognitive function, growth hormone and insulin-like growth factor 1 plasma levels in healthy older men

Circulating levels of growth hormone (GH) change during the process of aging. Decline of cognitive functioning with aging is also well established. In this study, we investigated whether insulin-like growth factor 1 (IGF-1) and the GH response to a challenge of GH-releasing hormone and GH-releasing peptide 6 were associated with age-sensitive cognitive functions, but not with functions that do not decline with aging, in 17 healthy male subjects aged between 66 and 76 years. In addition, relations with anthropometric measures were examined. Neuropsychological performance was scored on tests of variables not sensitive to aging (general knowledge, vocabulary, basic visual perception and reading ability), and of variables sensitive to aging (visuoconstructive ability, perceptual motor and mental processing speed, and verbal long-term memory). After correcting for education, the serum GH response was significantly associated with two age-sensitive cognitive tests (measures of mental processing speed), but with none of the tests not sensitive to aging. However, the direction of the association was opposite to the relation between IGF-1 and these cognitive tests: higher levels of GH response were associated with poorer cognitive performance, whereas higher levels of IGF-1 were associated with better performance. GH response, but not IGF-1, was inversely correlated with body mass index. The results are in accordance with previous research suggesting a disruption of the relation between IGF-1 and GH secretion in older age.