Low skeletal muscle mass index is independently associated with low bone mineral density in kidney transplant recipients: a retrospective observational cohort study

Background Osteoporosis and osteopenia are more frequent in patients who have received kidney transplants than in healthy individuals. Although osteoporosis and sarcopenia are closely related, only few studies have considered them in the post-transplantation period. We aimed to investigate the relationship between lower bone mineral density and skeletal muscle in kidney transplant recipients. Methods We included 371 patients in the maintenance phase of kidney transplantation (> 6 months after transplantation) followed-up at our institution from January to December 2019. The primary endpoint was the association between bone mineral density and skeletal muscle mass index. As secondary endpoints, in addition to skeletal muscle mass index, we investigated other factors associated with low bone mineral density, including kidney function and 25-hydroxy vitamin D (25(OH)D) concentration. Considering the possibility that factors affecting bone mineral density differ between men and women, we explored these factors separately for both sexes. Results Of the 371 participants, 243 (65.4%) were men. The median age and time after transplantation were 52 and 14 years, respectively. Univariate analysis showed that age, female sex, time since transplantation, cystatin C-based estimated glomerular filtration rate (eGFR(cysC)), 25(OH)D, and skeletal muscle mass index were associated with bone mineral density. Multivariate analysis showed associations of bone mineral density with eGFR(cysC), 25(OH)D, and skeletal muscle mass index. Multivariate analysis by sex showed significant associations with eGFR(cysC), hemoglobin, and skeletal muscle mass index in men and with age, eGFR(cysC), albumin, and skeletal muscle mass index in women. Bone mineral density was not associated with history of dialysis prior to transplantation or time since transplantation. Conclusions In kidney transplant recipients, an independent association between lower bone mineral density and skeletal muscle mass index was observed in both sexes.