Influence of birth size and body composition on bone mineral density in early adulthood: the PROGRAM study

Background/objectives Low bone mineral density (BMD) may lead to osteoporosis and is associated with increased fracture risk. Associations between BMD and various factors have been reported. Our objective was to investigate whether birth size, lean body mass (LBM) and fat mass (FM) are determinants of BMD of the total body (BMDTB) and the lumbar spine (BMDLS). Methods In the PROgramming factors for GRowth And Metabolism (PROGRAM) study of a cohort of 312 young adults aged 18-24 years, BMDTB and BMDLS were determined by dual-energy X-ray absorptiometry (DXA). Subsequently, differences in BMDTB and BMDLS were analysed in four subgroups: young adults born small for gestational age with short stature (SGA-S) or with catch-up growth (SGA-CU), or born appropriate for gestational age (AGA) with idiopathic short stature (ISS) or with normal stature (controls). Results Adult weight, LBM, FM and weight gain during childhood were the main positive determinants for BMDTB in early adulthood, whereas birth size had no influence (adjusted R-2 = 0.50). Gender, adult weight, LBM, FM and weight gain were the significant determinants of BMDLS. In the subgroups, after correction for age, gender and adult body size, the ISS group had a significantly lower BMDTB than controls but there was no difference in BMDLS between the subgroups. Conclusions Prenatal growth has no significant influence on BMDTB and BMDLS in early adulthood. Gender and postnatal growth, particularly weight gain, are the main positive determinants. To achieve a normal BMD in adulthood, healthcare workers should aim for a normal weight gain in children.