LAUSR

We read the publication on ‘Folate intake, serum folate, and risk of esophageal cancer: a systematic review and dose–response meta-analysis’ with a great interest (Ni et al., 2018). Ni et al. (2018) concluded that ‘folate can promote public health by decreasing esophageal cancer risk in a certain dosage range; otherwise, the protective effects might be reduced’. We would like to share ideas on this observation. First, the dose–response pattern might be affected by other confounding factors that cannot be control in the present study. In general, there are several disorders relating to folate in clinical practice. An important condition is the folate deficiency anemia, which is common among strict vegetarianism. Despite the low folate level background in those vegetarians, there has never been an observation on increased risk or incidence of esophageal cancer among the patients with folate deficiency anemia. Nevertheless, vegetarianism is reported to be protective against esophageal cancer (Rao et al., 1989). In addition, based on experience in our country in Indochina where thalassemia is very common, there is no diffference of esophageal cancer incidence between the thalassemic patients who receive regular folate supplementation and the general population who do not get folate supplementation. The relationship between folate and esophageal cancer is very complex and requires well-designed study, rather than a simple meta-analysis, for clarification.