Maternal vitamin D status during pregnancy and childhood bone mass at age 9 years: a longitudinal study

Increasing evidence suggests that the risk of osteoporotic fracture in adult life depends in part on environmental factors such as vitamin D and calcium nutriture during fetal and early postnatal life. Importantly, otherwise healthy pregnant women frequently are vitamin D-insufficient. Javaid et al therefore sought to determine whether maternal vitamin D status has a significant effect on skeletal growth in childhood. They evaluated data collected during a previous longitudinal study of maternal nutrition and fetal growth, including the responses to a lifestyle questionnaire, smoking status, use of dietary supplements, height and weight before and during pregnancy, and neonatal anthropomorphic measurements. 25(OH) vitamin D and calcium, albumin, phosphorus, alkaline phosphatase, and creatinine concentrations were measured in maternal serum collected at 34 weeks gestation and in umbilical cord blood samples. A total of 198 children born in 1991-1992 were followed up to age 9 years in an attempt to relate maternal vitamin D status to body size and bone mass. Women were considered to be vitamin D-deficient if their level was less than 11 μg/L, insufficient if it was 11 to 20 μg/L, and replete if it was more than 20 μg/L. In late pregnancy, nearly one half of the study participants had low vitamin D levels; 31% were vitamin D-insufficient and 18% were vitamin D-deficient. These women had children who, when evaluated at age 9 years, had reduced whole-body bone area, areal bone mineral density (BMD), and bone mineral content (BMC). When compared with the children whose mothers were vitamin D-replete, those whose mothers were vitamin D-deficient had a significantly lower whole-body BMC, whereas those whose mothers were vitamin D-insufficient had a smaller deficit. Adjusting for height in childhood did not substantially weaken this relationship. Lumbar spine BMC and areal BMD at age 9 did not correlate with bone area, milk intake, or physical activity at age 9. Maternal vitamin D status in late pregnancy was not related to birth weight or length, placental weight, abdominal circumference, head circumference, or height or lean body mass at age 9. However, late-pregnancy vitamin D levels did correlate with estimated ultraviolet B exposure and the use of vitamin D supplements. Children whose mothers took vitamin D supplements had significantly higher whole-body BMC and bone area, but not areal BMD, than children of nonusers. Cord blood calcium levels also significantly predicted whole-body BMC. These results indicate that women with vitamin D insufficiency are at increased risk to have children with bone density deficits and imply that supplementation of D-insufficient women might improve the bone mineral content of their offspring and thus ultimately lower the risk of fragility fracture. Because ultraviolet B exposure was significantly correlated with maternal vitamin D levels, vitamin D supplementation might be especially important when the last trimester of pregnancy coincides with the winter months.