Letter to the editor - dietary adjustment may be more than skin deep.

PURPOSE: To evaluate the sufficiency of the dietary adjustment of dietary risk factors, made in the recent study by Li et al. published in Cancer Causes & Controls. The main research question is: are the dietary adjustments in Li et al. sufficient enough to control for specific dietary food groups? METHODS: An evaluation of three methodological problems in Li et al.was performed; (1) the adjustment of total fruit intake, and how it relates to citrus fruit intake; (2) the adjustment of meat intake, and its relation to red and processed meat intake; (3) broad categorization of fish intake, and how it may limit interpretation. RESULTS: Adjusting for both total fruit intake and meat intake may not be enough to control the effect of specific dietary components which may affect melanoma risk, such as citrus fruit, and red and processed meat intake, causing an increased risk of residual confounding. Moreover, with no distinguishment between fresh and canned tuna in the dietary survey, significant limitations may be present. CONCLUSION: The dietary adjustments conducted in the study by Li et al. may not capture the intake of citrus fruit or red and processed meat, relevant to the risk of melanoma, and may induce residual confounding.

Milk consumption and the risk of type 2 diabetes: A systematic review of Mendelian randomization studies.

AIMS: Previously, no relationship between milk consumption and the risk of type 2 diabetes has been found in prospective cohorts. However, Mendelian randomization allows researchers to almost bypass much residual confounding, providing a more precise effect estimate. This systematic review aims to investigate the risk of type 2 diabetes and levels of HbA1c by assessing all Mendelian Randomization studies investigating this subject matter. DATA SYNTHESIS: PubMed and EMBASE were searched from October 2021 through February 2023. Inclusion and exclusion criteria were formulated to filter out irrelevant studies. Studies were qualitatively assessed with STROBE-MR together with a list of five MR criteria. Six studies were identified, containing several thousand participants. All studies used the SNP rs4988235 as the main exposure and type 2 diabetes and/or HbA1c as the main outcome. Five studies were graded as "good" with STROBE-MR, with one graded as "fair". For the six MR criteria, five studies were graded "good" in four criteria, while two studies were graded "good" in two criteria. Overall, genetically predicted milk consumption did not seem to be associated with an increased risk of type 2 diabetes. CONCLUSIONS: This systematic review found that genetically predicted milk consumption did not seem to increase the risk of type 2 diabetes. Future Mendelian randomization studies concerning this topic should consider conducting two-sample Mendelian Randomization studies, in order to derive a more valid effect estimate.