Serum levels of insulin-like growth factor-I are related to age and not to body composition in healthy women and men.
BACKGROUND
Aging is accompanied by decreased bone and lean body mass, increased fat mass, and reduced growth hormone (GH) axis function, reflected in diminished levels of insulin-like growth factor-I (IGF-I). Similar changes in body composition occur in nonelderly, GH-deficient adults and are reversible with GH administration, suggesting that diminished GH/IGF-I axis activity may contribute to such age-related changes. To determine the precise pattern of IGF-I decline with age, and to test the hypothesis that this decline is related to concomitant changes in body composition and bone metabolism independent of age, we conducted a cross-sectional survey in 351 healthy participants in the Baltimore Longitudinal Study of Aging.


METHODS
We evaluated relationships among IGF-I, age, and total and regional adiposity, as assessed by body mass index (BMI) and waist-to-hip ratio (WHR); lean body mass, as estimated from urinary creatinine excretion (Crex/ht); bone mineral density (BMD), as assessed by single and dual photon absorptiometry scanning; and circulating levels of parathyroid hormone (PTH), 1,25-(OH)2 D3, 25-OHD, and osteocalcin.


RESULTS
Serum IGF-I levels declined with age (p < .0001) in both men (r = -.51) and women (r = -.67). In men, the decline was linear, whereas IGF-I levels decreased faster in women < 45 years of age than in older women (p < .01) or in men (p < .001). IGF-I was inversely related to BMI (p < .005), WHR (p < .001), and PTH (p < .01) in women. IGF-I was positively related to BMD of the hip and radius in both genders (p < .0003) and to Crex/ht (p < .0005) and osteocalcin (p < .0001) in men. With increasing age, Crex/ht and BMD decreased (p < .0001) and WHR, PTH, and osteocalcin increased (p < .005) in both genders, whereas BMI increased only in women (p < .005). After adjustment for age, IGF-I was not significantly related to BMI, WHR, Crex/ht, or BMD in either gender. IGF-I was positively related to 1,25-(OH)2 D3 (p < .01) independently of age in women.


CONCLUSIONS
Advancing age, rather than declining serum levels of IGF-I, appears to be a major determinant of life-time changes in body composition and BMD in women and men.
O'Connor
K G
KG
Endocrine Section, Gerontology Research Center, National Institute on Aging (NIH), Baltimore, USA.
Tobin
J D
JD
Harman
S M
SM
Plato
C C
CC
Roy
T A
TA
Sherman
S S
SS
Blackman
M R
MR
D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000097:blood*; D001823:Body Composition / Q000502:physiology*; D015992:Body Mass Index; D015519:Bone Density; D002112:Calcifediol / Q000097:blood; D002117:Calcitriol / Q000097:blood; D005260:Female; D019382:Human Growth Hormone / Q000097:blood; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D008297:Male; D008875:Middle Aged; D015675:Osteocalcin / Q000097:blood; D010281:Parathyroid Hormone / Q000097:blood; D012016:Reference Values; D012044:Regression Analysis; D012727:Sex Characteristics
D010281:Parathyroid Hormone; D015675:Osteocalcin; D019382:Human Growth Hormone; D007334:Insulin-Like Growth Factor I; D002117:Calcitriol; D002112:Calcifediol