Serum insulin-like growth factor-1 in centenarians: Implications of IGF-1 as a rapid turnover protein

Background. It is well documented that serum insulin-like growth factor 1 (IGF-1) levels as well as growth hormone secretion decline with advancing age. Low levels of IGF-I are shown to be associated with low activity of growth hormone, low lean mass, and high body fat mass; however, in the elderly, the relationship has not been confirmed. Methods. We studied serum IGF-I levels in 49 centenarians, who are at the ultimate stage of physiological senescence, and investigated the possible relationship between IGF-1 and body mass index, lipid parameters, nutritional indices, physical and cognitive function, and frequency of hip fracture. As nutritional indices, serum levels of albumin, prealbumin, transferrin, and retinol binding protein were measured. Cognitive function of the centenarians was assessed by clinical dementia rating. Results. In the centenarians, the mean levels of IGF-1 were relatively low, indicating that there is an age-associated decline in IGF- 1 even in the extremely old age. We demonstrated a strong association of IGF- 1 with prealbumin and retinol binding protein (r² =.192,.195, respectively); however, there was no association with albumin, transferrin, or body mass index. Interestingly, centenarians with lower IGF-1 levels had a higher prevalence of definitive dementia. Conclusions. These data suggest that serum IGF-1 levels in the centenarians appeared to reflect their short-term nutritional status as a rapid turnover protein. It is also suggested that low levels of serum IGF- 1 may be involved in the progression of dementia in the oldest old.