Relationship between cognitive function, growth hormone and insulin-like growth factor I plasma levels in aged subjects

Basal growth hormone (GH) and Insulin-like growth factor I(IGF-I) as well as GH responses to GH-releasing hormone (GHRH) were studied in 22 subjects (7 females, 15 males), aged between 65 and 86 years. The study was aimed at Basal growth hormone (GH) and insulin-like growth factor I(IGF-I) as well as investigating the possible correlations between the age-dependent GH-IGF-I axis decline and the cognitive function - assessed by the Mini Mental State Examination (MMSE). The relationship between hormonal data, cognition and age, body weight, body mass index (BMI), some nutritional indices (triceps skinfolds, TSF, mid-arm circumference, MAC), and physical activity quantified by the physical functioning index (PFI) - were also analyzed. GH basal levels were within the normal range, while GH responses to GHRH were blunted in most cases. GH peaks after GHRH were directly correlated with GH basal values. IGF-I serum levels were found to be in the lower part of the reference range for adult subjects or below it. GH responses to GHRH, but not GH and IGF-I basal levels, were inversely correlated with subject age. GH secretion areas after GHRH were inversely correlated with BMI, but no further correlations between GH data and clinical or nutritional parameters were found. MMSE values directly correlated with MAC and PFI values. IGF-I levels were directly correlated with MMSE scores, being lowered in patients with more advanced cognitive deterioration, and with MAC values - the decrease of which is thought to reflect protein caloric malnutrition - but not with body weight, BMI, TSF and PFI. MMSE-related protein caloric malnutrition and decreased physical activity possibly take part in affecting IGF-I function in subjects with mild cognitive impairment and, reciprocally, IGF-I decrement might affect neuronal function.