ESPE Abstracts

Background: Vitamin D is a steroid hormone which contributes to the maintenance of calcium homeostasis and bone mineralization. As bone mineral accretion occurs mostly during the third trimester of pregnancy, mineral storages are deficient especially in the extremely low birth weight (ELBW <1000g) preterm infants at birth. Recent studies suggest that ELBW is a risk factor for compromised bone mineral density at adulthood, but the role of neonatal morbidity and vitamin D is controversial.

Methods: 38 adults born <34 gestation weeks, with a mean birth weight of 1397g (SD 301g), were recruited for the study at the mean age of 23.6 (SD 0.74) years. Vitamin D concentration (S-25OHD) was measured at the entry, mid-point, and end of the study. A dual energy X-ray absorptiometry for bone mineral density (BMD) was performed on 37/38 participants at the start and 35/38 at the end of the study. Vitamin D supplementation for one year was started to participants whose S-25OHD was under 80 nmol/l at the entry or mid-point evaluations (n = 35).

Results: The lowest lumbar spine BMD Z-score (mean -0.489, 95% CI -0.782 to -0.196), was significantly lower in the preterm born participants compared to age- and sex-specific reference values. BMD Z-scores were lower in the femoral neck (mean -0.332), but this finding was not statistically significant. During the intervention, S-25OHD levels increased from 60.3 nmol/l (SD 18.7 nmol/l) to 82.9 nmol/l (SD 25.8 nmol/l), with no association with BMD Z-scores. Lumbar spine or femoral neck BMD had no correlation with gestational age, birth weight or length, respiratory distress syndrome (RDS), surfactant treatment or antenatal steroids. Instead, postnatal dexamethasone treatment for RDS associated positively with lumbar spine BMD Z-Score (mean difference 0.93, 95% CI 0.27 – 1.59, P=0.007). Postnatal dexamethasone had no effect on adult weight, height, or BMI. Adult weight and BMI associated positively with lumbar spine (r = 0.337, P=0.041, r = 0.395, P=0.015) and femoral neck (rs = 0.457, P=0.004, rs = 0.451, P=0.005) BMD.

Conclusions: Bone mineral densities, especially in the lumbar spine, appear to be lower in the preterm born population. Adult weight and BMI associate with higher BMD both in the lumbar spine and femoral neck. Postnatal dexamethasone treatment associated with higher lumbar spine BMD, but the mechanism remains unclear and requires further research.