Context: Relationships between vitamin D exposure of the mother in pregnancy and skeletal development of the child are poorly understood.
Objectives: Our objectives were to establish whether background UVB levels in the third trimester of pregnancy are related to bone mineral content (BMC) of the child, and to examine whether these relationships are explained by effects on height, fat, or lean mass.
Design: This was a prospective cohort study.
Setting: The Avon Longitudinal Study of Parents and Children, a population-based birth cohort, was studied.
Participants: A total of 6995 boys and girls with a mean age of 9.9 yr was studied.
Outcome measures: Prespecified analyses of relationships between background UVB levels in the third trimester of pregnancy, and total body less head BMC, bone area (BA), bone mineral density, and area-adjusted BMC as measured by dual-energy x-ray absorptiometry scans at 9.9 yr were performed.
Results: Maternal UVB exposure was positively related to BMC (g) [9.6 (5.3, 13.8)], BA (cm(2)) [8.1 (4.3, 11.9)], and bone mineral density (g/cm(-2)) [0.003 (0.001, 0.004)], but not area-adjusted BMC (g) [0.69 (-0.22, 1.56)], suggesting an effect on bone size. Both height-dependent (cm) [0.18 (0.03, 0.32)] and height-independent (cm(2)) [4.1, (2.0, 6.2)] effects contributed to this association between UVB and BA. Although maternal UVB exposure was also related to lean mass (g) [163 (89, 237)], a positive association between UVB and BA persisted after adjusting for both height and lean mass [2.8 (1.0, 4.6)].
Conclusions: Maternal UVB exposure is related to bone size at age 9.9 yr independently of height and lean mass, suggesting that vitamin D status in pregnancy exerts direct effects on periosteal bone formation in subsequent childhood.