BACKGROUND: In a cross-sectional study in 403 healthy, independently
living elderly men (mean age 78 years), we determined which are the main
physiological determinants of functional ability in the elderly, and which
components of the somatotropic system contribute to the maintenance of
functional ability. METHODS: Functional ability was assessed by the number
of problems in activities of daily living and by a measure of physical
performance. Other physical characteristics included leg extensor
strength, bone mineral density of total body and proximal femur, and body
composition, including lean mass and fat mass. Serum insulin-like growth
factor (IGF)-I and its binding proteins (IGFBP) -1, -2 and -3
concentrations were all measured by RIA. RESULTS: Muscle strength was
related to a lower degree of disability. Further, it was positively
related to physical performance and bone mineral density (all P<0.001).
Fat mass influenced activities of daily living and physical performance
negatively and bone mineral density positively (all P<0.001). Serum
concentrations of IGF-I and IGFBP-3 were not related to any of the
physical characteristics. High serum IGFBP-2 concentrations were related
to a higher degree of disability (P<0.001), a lower physical performance
(P=0.006), muscle strength (P=0.002), bone mineral density of proximal
femur (P=0.007), lean mass and fat mass (both P<0.001). Serum insulin and
IGFBP-1 concentrations were independently, positively related to lean mass
(P=0.003) and fat mass (P<0.001). CONCLUSIONS: In independently living
elderly men, functional ability appears to be determined by muscle
strength (positive) and fat mass (negative). Low serum IGFBP-2
concentrations are a powerful indicator for overall good physical
functional status, probably inversely reflecting the integrated sum of
nutrition and the biological effects of growth hormone, IGF-I and insulin
