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Clinical Research

Careful data extraction in meta-analysis: the case of maternal caffeine intake during pregnancy and low-birth weight, childhood overweight, and obesity

International Journal of Obesity volume 45, pages 713–714 (2021)Cite this article

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In a recent issue of the journal, Jin et al. [1] summarized findings from earlier cohort studies on the association between maternal caffeine intake during pregnancy and low-birth weight (LBW), childhood overweight, and obesity. They reported a significant direct association between maternal caffeine intake during pregnancy and risk of LBW and childhood overweight and obesity. Although these findings are interesting and valuable, some critical points need to be considered when interpreting these findings. It must be kept in mind that data extraction from previous publications on a specific issue should be done carefully to avoid misleading results. In their paper, figure 2 provides a summary estimate of the association between maternal caffeine intake during pregnancy and LBW risk based on 11 studies. For most of the included studies, Jin et al. used RRs and ORs for LBW comparing the highest intake versus the lowest intake of caffeine during pregnancy; however, the study of Okubo et al. [2] and Chen et al. [3] have reported RRs for 100 mg caffeine intake per day rather than for the highest vs. lowest intake. Jin and Qiao combined these dose-response RRs with other RRs for the highest vs. lowest categories, which would result in a bias. They also focus inappropriately on highest vs lowest exposure categories, even when those categories differ widely between studies. Of note, a consistent presentation of the results across different studies is required to perform an effective review. Therefore, no implications can be drawn from Jin and Qiao’s pooled relative risks because we cannot say what level of intake the increased risks relate to or even what they are relative to. Another point is that the study of Martin et al. [4] have reported covariate-adjusted RRs in their study, while the authors have only used the crude RRs they reported. Given the contribution of other variables to LBW, it is very important to identify the independent association of maternal caffeine intake during pregnancy and risk of LBW. Jin and Qiao have provided an inadequate search strategy (a requirement of PRISMA) and missed out a large number of relevant studies of maternal caffeine intake and birth weight that have been identified in previous reviews [5, 6]. They have also not provided a full list of excluded studies to explain why they have not included studies that previous more focused meta-analyses have considered relevant (another requirement of PRISMA). Moreover, they combined the studies of maternal caffeine intake with studies of coffee which do not quantify the caffeine content, and ignore caffeine from other sources. In addition, the authors did not clearly state how many studies were included in the dose-response analysis, which in turn may limit the interpretation of findings. Findings from their meta-analysis on LBW indicated the evidence of heterogeneity, but the source of this heterogeneity was not explored through stratification or meta-regression; however, the exploration of heterogeneity is a requirement of PRISMA. In addition, there is no mention of the MOOSE guidance anywhere. Finally, the meta-analysis of the association between maternal caffeine intake and childhood overweight or obesity is more novel, but there are only four studies identified comparing highest vs lowest, and only two with enough information for the authors to do the correct dose–response analysis.

In conclusion, there is a great value in summarizing the association between maternal caffeine intake during pregnancy and risk of LBW, childhood overweight, and obesity in a meta‐analysis; however, methodological issues should be considered to reach an accurate conclusion on this issue.

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References

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Authors and Affiliations

  1. Department of Community Nutrition, School of Nutritional Sciences and Dietetics, Tehran University of Medical Sciences, Tehran, Iran

    Sanaz Soltani, Mohammadreza Askari, Leila Azadbakht & Ahmad Esmaillzadeh

  2. Endocrinology and Metabolism Research Center, Endocrinology and Metabolism Clinical Sciences Institute, Tehran University of Medical Sciences, Tehran, Iran

    Bagher Larijani

  3. Diabetes Research Center, Endocrinology and Metabolism Clinical Sciences Institute, Tehran University of Medical Sciences, Tehran, Iran

    Leila Azadbakht

  4. Obesity and Eating Habits Research Center, Endocrinology and Metabolism Molecular-Cellular Sciences Institute, Tehran University of Medical Sciences, Tehran, Iran

    Ahmad Esmaillzadeh

  5. Department of Community Nutrition, School of Nutrition and Food Science, Isfahan University of Medical Sciences, Isfahan, Iran

    Ahmad Esmaillzadeh

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  1. Sanaz Soltani
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Correspondence to Ahmad Esmaillzadeh.

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Soltani, S., Askari, M., Larijani, B. et al. Careful data extraction in meta-analysis: the case of maternal caffeine intake during pregnancy and low-birth weight, childhood overweight, and obesity. Int J Obes 45, 713–714 (2021). https://doi.org/10.1038/s41366-021-00746-0

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