Childhood BMD not directly affected by maternal smoking during pregnancy
MedWire News: Daughters, but not sons, of mothers who smoke cigarettes during pregnancy have higher bone mass at age 10 years than children whose mothers did not smoke during pregnancy, but the association seems to be indirect, UK research shows.
A similar effect was observed among girls whose fathers smoked throughout the mother's pregnancy, suggesting that the association "appears to be due to familial factors related to parental smoking influencing increased offspring adiposity rather than a direct intrauterine effect," say the researchers.
Corrie Macdonald-Wallis and colleagues from the University of Bristol assessed the associations of parental smoking during pregnancy with skeletal size and bone density at mean age of 9.9 years in 7121 children participating in the Avon Longitudinal Study of Parents and Children.
They found that daughters of mothers who smoked in any trimester had total (excluding the skull) bone mineral content (BMC), bone area, and bone mineral density that were all a significant 0.13 standard deviations (SD) higher than those of mothers who did not smoke. Similar results were observed at the spine.
In contrast, there was no association between a mother's smoking status during pregnancy and her son's bone measurements at any of the sites assessed.
Paternal smoking associations were similar to maternal associations for sons and daughters, with no statistical evidence for a difference between maternal and paternal effects.
After adjustment for the child's birth weight and gestational age, there were increases in associations between bone measurements and maternal smoking, whilst paternal associations did not change, indicating that "maternal smoking has a negative intrauterine effect on the accrual of bone mass by the fetus," says the team.
Conversely, when the data were adjusted for the child's height and weight at age 9.9 years, all maternal and paternal relationships were completely attenuated. The relationship was driven mainly by the child's weight, they note.
"Since no relationships were found between maternal smoking and area-adjusted BMC, which reflects 'volumetric' BMC, it appears that the associations are working through skeletal size rather than density," say Macdonald-Wallis et al.
"It therefore seems most plausible that our associations are not explained by intrauterine effects, but rather that unmeasured aspects of the shared family environment which are associated with parental smoking, such as diet or level of physical activity, influence increased weight gain and greater bone mass in the children," they conclude in the journal Osteoporosis International.
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By Laura Dean