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Reply to ‘Healthy dietary indices and risk of depressive outcomes: a systematic review and meta-analysis of observational studies’

Molecular Psychiatry volume 25, pages 3119–3120 (2020)Cite this article

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We recently read with considerable interest the paper entitled “Healthy dietary indices and risk of depressive outcomes: a systematic review and meta-analysis of observational studies”, by Lassale et al. [1]. We commend the authors for this important research and agree that the data are of considerable public health importance. However, upon reading the paper, we noted a number of methodological limitations with the conduct of this meta-analysis.

First, the authors state in the statistical analysis section on page 2: “For each dietary score (exposure variable), we conducted separate meta-analyses dependent on study design (cross-sectional vs. longitudinal)”. However, it appears from the actual reporting of the results in the figures that the authors pooled data from cross-sectional, case−control and cohort studies together (in addition to separate pooled effect sizes) and produced an overall effect size for all study design types. For example, in Fig. 1, in which the pooled effect size of cohort studies was 0.67 (95% CI: 0.55−0.82) and that of cross-sectional studies was 0.66 (95% CI: 0.35−1.24), the paper also reported a combined pooled effect size (OR = 0.69; 95% CI: 0.59−0.82) [1]. We suggest readers focus predominantly on the pooled effect sizes for the distinct study designs rather than on the overall pooled effect size, given that it is not methodologically correct to pool the study designs in this way.

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References

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Authors and Affiliations

  1. National Research Council, Neuroscience Institute, Aging Branch, Padova, Italy

    Nicola Veronese

  2. The Cambridge Centre for Sport and Exercise Sciences, Anglia Ruskin University, Cambridge, UK

    Lee Smith

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  1. Nicola Veronese
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  2. Lee Smith
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Correspondence to Nicola Veronese.

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Veronese, N., Smith, L. Reply to ‘Healthy dietary indices and risk of depressive outcomes: a systematic review and meta-analysis of observational studies’. Mol Psychiatry 25, 3119–3120 (2020). https://doi.org/10.1038/s41380-019-0462-9

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