Growth factor proteins linked to bone density in older men
MedWire News: Insulin-like growth factor (IGF)-I and insulin-like growth factor binding protein (IGFBP)-3 are independently associated with bone mineral density (BMD), a study of European men shows.
A second binding protein, IGFBP-1, was also associated BMD at the heel, but the effect was explained by confounding factors such as physical activity level, smoking status, alcohol consumption, and sex hormone levels.
"It is well established that the growth hormone IGF-I axis plays an important role in bone metabolism, including stimulating osteoblast function, and inhibiting collagen matrix degradation," explain Terence O'Neill (The University of Manchester, UK) and colleagues.
However, less than 1% of the total serum IGF-I is freely circulating; the remainder is bound to high-affinity IGFBPs, which play an important role in regulating IGF-I activity and bioavailability, they add.
The researchers used data from the multicenter European Male Ageing Study to examine the influence of IGFBP-1, IGFBP-3, and IGF-I on bone health in 3057 European men aged 40-79 years.
Each man underwent quantitative ultrasound of the calcaneus, which the researchers used to calculate the estimated BMD (eBMD). The participants also completed a lifestyle questionnaire and provided blood samples, which were tested for serum levels of IGFBP-1, IGFBP-3, IGF-I, estradiol (E2), and sex hormone-binding globulin (SHBG).
After adjusting for age, recruitment location, and body mass index, the researchers found that each standard deviation (SD) increase in IGFBP-1 level was associated with a 0.021 g/cm2 decrease in eBMD.
In contrast, each SD increase in IGFBP-3 and IGF-I was associated with respective eBMD increases of 0.021 and 0.040 g/cm2.
IGFBP-3 and IGF-I remained significantly associated with eBMD after further adjustment for physical activity, current smoking, alcohol consumption, and free E2 and SHBG levels, whereas the association with IGFBP-1 was attenuated by these factors.
"This is consistent with the notion that IGFBP-1 has less influence on IGF-I activity than IGFBP-3," write O'Neill and co-authors in the journal Osteoporosis International.
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By Laura Dean