Body Composition in Adults Born at Very Low Birthweight—A Sibling Study

Background: Individuals born preterm at very low birthweight (VLBW, < 1500 g) tend to attain a smaller adult body size compared with term-born peers but less is known regarding specific body composition characteristics. Objectives: We aimed to assess whether adults born at VLBW have less beneficial body composition characteristics, potentially mediating the association between VLBW birth and cardiometabolic disease. Sibling controls were used to account for the potential influence of shared genetic and/or lifestyle factors. Methods: This cohort study featured 77 adults born at VLBW and 70 term-born siblings. Dual-energy X-ray absorptiometry assessment took place at a mean age of 29 years. Fat mass (FM) distribution was calculated by dividing appendicular by truncal FM. Appendicular skeletal mass (ASM) measurements were used to calculate two indices: Skeletal mass index (SMI, ASM divided by height squared) and ASM/BMI (ASM divided by body mass index). Data were analysed by linear mixed models. An exploratory analysis subdivided the VLBW group by size at gestational age [small or appropriate for gestational age (SGA, defined as a birthweight < 2 SD, or AGA)]. Results: Participants born at VLBW were lighter (−4.7 kg, 95% CI −8.2, −1.2) and shorter (−4.3 cm, 95% CI −6.2, −2.4) than sibling peers. After controlling for sex, age, and maternal factors, they had lower limb/trunk fat ratios (−0.06, 95% CI −0.11, −0.003), LBM (−2.02 kg, 95% CI −3.92, −0.12), ASM (−1.22 kg, 95% CI −2.14, −0.30) and ASM/BMI (−0.05, 95% CI −0.10, −0.004). FM and SMI did not differ between groups. In the subgroup analysis, findings were limited to those born VLBW + SGA. Conclusions: Individuals born at VLBW had, on average, lower limb/trunk fat ratios and lower relative ASM compared with term-born siblings. A more centralised fat distribution, as well as lower appendicular muscle mass, could potentially mediate the association between VLBW birth and cardiometabolic risk.