Fish oil in pregnancy linked to child weight gain and metabolic risks

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A randomized controlled trial published in The American Journal of Clinical Nutrition claims that fish oil supplementation during pregnancy can increase the risk of weight gain and metabolic syndrome in the offspring at the age of ten. 

Study: Fish oil supplementation during pregnancy, anthropometrics, and metabolic health at age ten: A randomized clinical trial


The prevalence of overweight and obesity has increased significantly in children and adolescents over the past decades. Environmental exposures during pregnancy are known to play a significant role in modulating the body composition of infants later in life. Among various environmental exposures, intake of fatty fish-derived n-3 long-chain polyunsaturated fatty acids (LCPUFAs) has gained considerable attention because of their known health benefits.

Several observational human studies and animal studies have shown that fatty fish or LCPUFAs intake during pregnancy is associated with lower body mass index (BMI) and healthier metabolic profiles in the offspring.       

The authors of this paper have previously conducted a randomized controlled trial of fish oil supplementation during the third trimester of pregnancy to determine its impact on the growth and body composition of the offspring at the age of six years. They have observed an induction in BMI and fat, muscle, and bone mass among the offspring.

In this paper, the researchers reported the findings of their extended follow-up trial that included metabolic health assessment of the offspring at the age of ten years.

About the randomized controlled trial

The trial was conducted on a total of 736 pregnant women and their offspring who were participating in the Copenhagen Prospective Studies on Asthma in Childhood mother-child cohort. The pregnant women were randomly categorized during week 24 of pregnancy into the intervention group and the control group.

In the intervention and control groups, participants were supplemented daily with 2.4 grams of n-3 LCPUFAs or look-alike capsules of olive oil, respectively. The supplementation was continued until one week after birth.

Parameters assessed in the trial included anthropometric measurements, body composition, blood pressure, triglyceride and cholesterol concentrations, fasting glucose and C-peptide concentrations, and a metabolic syndrome score.

Important observations

A total of 688 children with one or more anthropometric measurements were included in the analysis. Of them, 341 corresponded to the intervention group, and 347 corresponded to the control group.

The assessment of children's BMI, growth, and body composition at the age of ten revealed that the intervention group children have significantly higher BMI than the control group children. They were also at higher risk of being overweight than control group children.

However, the differences in BMI and risk of overweight observed between the intervention and control groups became attenuated after adjusting for strong risk factors related to childhood growth, including maternal BMI before pregnancy, smoking during pregnancy, parity, and duration of exclusive breastfeeding.

Regarding body composition, the study found that children in the intervention group have non-significantly higher lean mass, fat mass, and fat percentage than those in the control group.

Regarding metabolic syndrome outcomes, the study found that the supplementation of LCPUFAs during pregnancy does not impact blood levels of glucose and lipids, waist circumference, and blood pressure in corresponding children at age ten. However, all the estimates pointed out an unhealthier metabolism in the intervention group children.

The estimation of metabolic syndrome scores revealed that children in the intervention group had higher mean scores than those in the control group.

The findings of the mediation analysis revealed that the observed outcomes in the intervention group children are not mediated by their level of physical activity, eating habits, and puberty stage. Furthermore, no significant difference in the effect of LCPUFA supplementation on anthropometric and metabolic measures was observed between boys and girls at the age of ten.

Study significance

The study finds that children of mothers who received LCPUFA supplementation during the third trimester of pregnancy have significantly higher BMI and risk of being overweight at the age of ten years. They also have a tendency of increased fat percentage and higher metabolic syndrome scores.

Overall, the study findings suggest that fish oil or LCPUFA supplementation during pregnancy may have negative health impacts on the offspring.

Journal reference:
Dr. Sanchari Sinha Dutta

Written by

Dr. Sanchari Sinha Dutta

Dr. Sanchari Sinha Dutta is a science communicator who believes in spreading the power of science in every corner of the world. She has a Bachelor of Science (B.Sc.) degree and a Master's of Science (M.Sc.) in biology and human physiology. Following her Master's degree, Sanchari went on to study a Ph.D. in human physiology. She has authored more than 10 original research articles, all of which have been published in world renowned international journals.


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