Vitamin D during pregnancy in relation to childhood growth, overweight and obesity

Sammanfattning: The aim of this thesis is to investigate the association between maternal vitamin D intake and status in pregnancy and the child´s growth and risk of overweight and obesity in childhood. Data from the Norwegian Mother, Father and Child Cohort Study (MoBa) and the Swedish GraviD study were used in Paper I-IV and Paper III-IV, respectively. Paper I include investigations of vitamin D status and its determinants, and vitamin D intake. Overall, 48% of women had vitamin D insufficiency and 61% had a vitamin D intake below the recommended 10 µg/day. Higher vitamin D status was associated with higher vitamin D intake, blood sampling between spring to autumn, use of solarium, higher education and age, origin from high income country, lower pre-pregnancy body mass index (BMI), and not smoking during pregnancy. In Paper II, we investigated the associations between maternal vitamin D intake and childhood growth and risk of overweight from birth up to 8 years. Among mothers with normal pre-pregnancy BMI, a vitamin D intake ≥10µg/day was associated with lower weight growth trajectories during infancy and with child overweight in preschool years. The results indicated associations in opposing directions in children of mothers with pre-pregnancy overweight or obesity. In Paper III, we investigated the association between maternal vitamin D status and classes of infant BMI growth trajectories up to 2 years of age. Lower maternal vitamin D status was associated with a higher BMI growth trajectory class during the first 2 years of life in MoBa, but not in GraviD. In Paper IV, we investigated the association between maternal vitamin D status and the child´s BMI and risk for overweight at 5 years of age. Low maternal vitamin D status was associated with lower childhood BMI, but not with overweight. Compilation of the scientific literature indicate that maternal vitamin D intake and status during pregnancy may play a role in childhood growth and risk of overweight or obesity. However, there is not sufficient evidence to conclude if the associations are causal. If there is a causal effect of maternal vitamin D status on childhood growth or risk of overweight and obesity, it is likely small and with no clinically important effect.