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Effect of fish oil supplementation in pregnancy on bone, lean, and fat mass at six years: randomised clinical trial

BMJ 2018; 362 doi: (Published 04 September 2018) Cite this as: BMJ 2018;362:k3312


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  1. Rebecca Kofod Vinding, medical doctor1 2,
  2. Jakob Stokholm, senior researcher1,
  3. Astrid Sevelsted, statistician1,
  4. Tobias Sejersen, medical doctor1 2,
  5. Bo L Chawes, associate professor1,
  6. Klaus Bønnelykke, associate professor1,
  7. Jonathan Thorsen, medical doctor1,
  8. Laura D Howe, epidemiologist3,
  9. Martin Krakauer, nuclear medicine consultant4,
  10. Hans Bisgaard, professor1
  1. 1COPSAC, Copenhagen Prospective Studies on Asthma in Childhood, Herlev and Gentofte Hospital, University of Copenhagen, Copenhagen, Denmark
  2. 2Department of Pediatrics, Naestved Hospital, Naestved, Denmark
  3. 3MRC Integrative Epidemiology Unit at the University of Bristol, School of Social and Community Medicine, University of Bristol, Bristol, UK
  4. 4Department of Clinical Physiology and Nuclear Medicine, Herlev and Gentofte Hospital, University Hospital of Copenhagen, Denmark
  1. Correspondence to: H Bisgaard bisgaard{at}
  • Accepted 17 July 2018


Objective To examine the effect of supplementation with n-3 long chain polyunsaturated fatty acids (n-3 LCPUFA) in pregnancy on anthropometry and body composition in offspring.

Design Double blinded, randomised controlled trial.

Setting Copenhagen Prospective Studies on Asthma in Childhood2010 cohort.

Participants 736 pregnant women and their offspring.

Intervention n-3 LCPUFA (fish oil) or control (olive oil) daily from pregnancy week 24 until one week after birth.

Main outcome measures Height/length, weight, head, and waist measurements and body composition from dual energy x ray absorptiometry (all pre-specified secondary endpoints of the n-3 LCPUFA trial; the primary outcome for the trial was persistent wheeze/asthma).

Results The mean body mass index (BMI) z score was increased between age 0 and 6 years in the fish oil supplementation group compared with the control group (0.14 (95% confidence interval 0.04 to 0.23); P=0.006). At 6 years, supplementation was associated with a higher BMI z score (0.19 (0.06 to 0.32); P=0.004), a higher weight/height (3.48 (0.38 to 6.57) g/cm; P=0.03), and a larger waist circumference (0.6 (0.0 to 1.2) cm; P=0.04) but not a higher proportion of obese children, using International Obesity Task Force grades. The dual energy x ray absorptiometry scan at age 6 years showed a higher total mass (395.4 (86.6 to 704.3) g; P=0.01) in the supplementation versus the control group, explained by a higher lean mass (280.7 (98.9 to 462.4) g; P=0.002), a higher bone mineral content (10.3 (2.3 to 18.1) g; P=0.01), and a non-significantly higher fat mass (116.3 (−92.9 to 325.5) g; P=0.28), but no differences were seen in total body fat or lean mass percentage.

Conclusion Fish oil supplementation from the 24th week of pregnancy led to a higher BMI in the offspring from 0 to 6 years of age but not an increased risk of obesity at age 6. The body composition at age 6 years in children given fish oil supplementation was characterised by a proportional increase in lean, bone, and fat mass suggesting a general growth stimulating effect of n-3 LCPUFA.

Trial registration NCT00798226


  • Contributors: HB was involved in the conception, design, and conduct of the trial and in acquisition, analysis, and interpretation of the data. All co-authors contributed substantially to the analysis and interpretation of the data and provided important intellectual input. RKV wrote the first draft of the manuscript. All authors agreed that the accuracy and integrity of the work has been appropriately investigated and resolved, and all approved the final version of the manuscript. The corresponding author had full access to the data and had final responsibility for the decision to submit for publication. The corresponding author attests that all listed authors meet authorship criteria and that no others meeting the criteria have been omitted. HB is the guarantor.

  • Funding: All funding received by COPSAC is listed on The Lundbeck Foundation (grant no R16-A1694), the Ministry of Health (grant no 903516), the Danish Council for Strategic Research (grant no 0603-00280B), and the Capital Region Research Foundation have provided core support to the COPSAC research centre. LDH is funded by a UK Medical Research Council career development award (MR/M020894/1) and works in a unit funded by the UK Medical Research Council and the University of Bristol (MC_UU_12013/5). The funding agencies did not have any role in the design and conduct of the trial; the collection, management, and interpretation of the data; or the preparation, review, or approval of the manuscript. No pharmaceutical company was involved in the trial.

  • Competing interests: All authors have completed the ICMJE uniform disclosure form at (available on request from the corresponding author) and declare: no support from any organisation for the submitted work other than that described above; no financial relationships with any organisations that might have an interest in the submitted work in the previous three years; no other relationships or activities that could appear to have influenced the submitted work.

  • Ethical approval: The trial was conducted in accordance with the guiding principles of the Declaration of Helsinki and was approved by the local ethics committee (H-B-2008-093), and the Danish Data Protection Agency (2015-41-3696). Both parents gave written informed consent before enrolment.

  • Data sharing: Technical appendix, statistical code, and dataset available from the corresponding author at bisgaard Participants’ consent was not obtained, but the presented data are anonymised and risk of identification is low.

  • Transparency statement: The lead author (the manuscript’s guarantor) affirms that this manuscript is an honest, accurate, and transparent account of the study being reported; that no important aspects of the study have been omitted; and that any discrepancies from the study as planned (and, if relevant, registered) have been explained.

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