Objective: Vitamin D is important in bone health. However, potential relationships of concomitant vitamin D deficiency with growth hormone deficiency (GHD) and the possibility that vitamin D inadequacy may alter the skeletal effects of growth hormone (GH) replacement therapy have not been adequately evaluated.
Methods: A prospective study was conducted in adult-onset GHD patients treated with recombinant human GH (rhGH) for 2 years. Trabecular bone score (TBS), lumbar spine (LS) bone mineral density (BMD), total hip (TH) BMD, and 25-hydroxyvitamin D (25(OH)D) levels were assessed at baseline and 24 months. The study cohort was divided based on 25(OH)D levels into 2 groups with the cutoff defined as the 50(th) percentile at each follow-up time point.
Results: Fifty-seven patients (29 males/28 females, mean age 34.4 years) were studied. After 24 months of GH replacement, LS BMD increased by 7.6% and TH BMD increased by 4.5% (both P<.05), with no difference according to 25(OH)D levels. TBS increased (+1.39 ± 3.6%) in those whose 25(OH)D was above the 50(th) percentile but decreased (-1.36 ± 5.6%, P<.05) in the cohort below the 50(th) percentile of 25(OH)D. Positive correlations were observed between baseline levels of IGF-1 and 25(OH)D (R = 0.37, P<.001) and between 24-month 25(OH)D and TBS (R = 0.25, P<.05).
Conclusion: A differential effect of GH on TBS change was observed; TBS increased only in the cohort with 25(OH)D above the 50(th) percentile. Vitamin D sufficiency may be required to obtain optimal effects of GH treatment on bone quality, as assessed by TBS, in GHD adults.
Abbreviations: AO-GHD = adult-onset GHD BMD = bone mineral density BMI = body mass index Ca = calcium CTx = carboxyterminal collagen crosslinks CV = coefficient of variation DXA = dual energy X-ray absorptiometry ECLIA = enzyme-labeled chemiluminescent immunometric assay GH = growth hormone GHD = growth hormone deficiency IGF-1 = insulin-like growth factor 1 LS BMD = lumbar spine BMD OC = osteocalcin 25(OH)D = 25-hydroxyvitamin D P = phosphorus PTH = parathyroid hormone rhGH = recombinant human GH TBS = trabecular bone score TH BMD = total hip BMD.