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In Reply We are delighted that our article has generated interest in the ways that fish intake during pregnancy could affect the risk of childhood obesity. We welcome the Letters to the Editor appearing in this issue of JAMA Pediatrics highlighting vitamin D and tributyltin as nutritional and environmental constituents in fish.
Hyde et al suggest that vitamin D contained in fish could play a role in the association between fish intake during pregnancy and childhood obesity. Maternal serum 25-hydroxyvitamin D, the major circulating form of vitamin D, diffuses freely across the placenta, and fetal exposure depends solely on maternal concentrations. There is indeed increasing evidence that vitamin D status in pregnancy may influence normal fetal growth and development1; however, the association with child adiposity remains uncertain.2- 5 Vitamin D is obtained primarily via exposure to UV-B radiation in sunlight and to a limited extent from dietary sources. However, the type of fish consumed is an important predictor of dietary vitamin D intake. Fatty fish, in contrast to lean fish, is rich both in vitamin D and ω-3 long-chain polyunsaturated fatty acids but is also a common route of exposure to persistent organic pollutants owing to their lipophilic characteristics. In our analysis, we did not find evidence for an association of fatty fish intake with childhood overweight and obesity. A possible explanation is the high content of fatty fish in beneficial nutrients, which may outweigh or mask the potential negative effects of pollutants. Another explanation might be the relatively low fatty-fish consumption levels across cohorts (median, 0.49 times/week; IQR, 0.00-0.98), which may have undermined the possibility to detect any association. Given the high prevalence of vitamin D deficiency and increasing rates of childhood obesity, further studies are needed to study the effect of serum 25-hydroxyvitamin D concentration in pregnancy on childhood obesity risk, and experimental studies are required to elucidate potential mechanisms.
Stratakis N, Zeegers MP, Chatzi L. Fish Intake During Pregnancy and Offspring Adiposity—Reply. JAMA Pediatr. 2016;170(8):809-810. doi:10.1001/jamapediatrics.2016.1029