Maternal vitamin D and offspring fracture risk: the Vitamin D in Pregnancy study

Vitamin D is important for bone health and strength. Previous studies report 25-hydroxyvitamin D (25(OH)D) exposure during pregnancy may impact offspring bone health later in life. In this study, maternal 25(OH)D at recruitment was associated with a lower fracture risk in boys and an increased fracture risk in girls at 28-32 weeks gestation.

Maternal 25-hydroxyvitamin D (25(OH)D) in pregnancy has been shown to be associated with offspring bone measures in some studies, but few have examined fracture risk. We aimed to determine associations between maternal vitamin D status and offspring fracture risk.

In total, 475 mother-child pairs participating in the Vitamin D in Pregnancy study in southeastern Australia were recruited. Maternal serum samples were taken at recruitment (< 16 weeks gestation) and/or 28-32 weeks gestation and analysed for 25(OH)D. Incident fractures in children were ascertained from date of birth (2002-2004) until December 31, 2012. Cox proportional hazard models included maternal age at recruitment, offspring sex, birth weight, gestation length and season of vitamin D sample.

Complete follow-up data were available for 400 children (median age = 9.5 years). There were 68 (17.0%) children who sustained at least one fracture. Higher maternal 25(OH)D (per 10 nmol/L) in early gestation was weakly associated with a decreased fracture risk in boys (HR 0.82; 95% CI 0.68, 0.99; p = 0.048) but not girls (HR 1.10; 95% CI 0.98, 1.25; p = 0.11). At late gestation, higher maternal 25(OH)D was associated with increased fracture risk in girls (HR 1.11; 95% CI 1.01, 1.23; p = 0.038) but not boys (HR 0.94; 95% CI 0.80, 1.10; p = 0.42). No statistically significant relationships were detected in analyses investigating 25(OH)D as a categorical variable.

There is some evidence that higher maternal 25(OH)D at recruitment was associated with lower fracture risk in boys, while higher maternal 25(OH)D at 28-32 weeks gestation was associated with an increased fracture risk in girls.