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

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?

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.

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.

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.