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This systematic review and meta-analyses aimed to assess whether malnutrition may increase the incidence of oral cancer. Following the PRISMA statement, the research was conducted on PubMed, Scopus, and MEDLINE via OVID without any time restrictions. The risk of bias was assessed, and the quality of evidence for each performed meta-analysis was evaluated using the Grading of Recommendations Assessment, Development and Evaluation (GRADE) framework. Sixty-one articles met the inclusion criteria and seven studies underwent quantitative evaluation. For our meta-analysis on hypovitaminosis B, three studies with a total of 90,011 patients were included. An odds ratio of 2.22 was found. Our meta-analysis on the correlation between vitamin C and oral cancer included one study with a total of 866 patients and the derived odds ratio was 1.06. Our meta-analysis on the relationship between vitamin D deficiency and the incidence of oral cancer included three studies with a total of 12,087 patients and the odds ratio was −2.58. The GRADE system showed a moderate strength of evidence due to the presence of studies with a high risk of bias and high indirectness of the data given. The present findings suggest that an inadequate intake of vitamins, particularly vitamin D, poses a risk for the onset of oral cancer.

Even if the relationship between immunosuppression and increased incidence of systemic cancers is well known, there is less awareness about the risk of developing oral cancer in immunosuppressed patients. The aim of this review was to evaluate the association between immunosuppression and the development of oral cancer. Two authors independently and, in duplicate, conducted a systematic literature review of international journals and electronic databases (MEDLINE via OVID, Scopus, and Web of Science) from their inception to 28 April 2023. The assessment of risk of bias and overall quality of evidence was performed using the Newcastle–Ottawa Scale and GRADE system. A total of 2843 articles was identified, of which 44 met the inclusion criteria and were included in either the qualitative or quantitative analysis. The methodological quality of the included studies was generally high or moderate. The quantitative analysis of the studies revealed that immunosuppression should be considered a risk factor for the development of oral cancer, with a percentage of increased risk ranging from 0.2% to 1% (95% CI: 0.2% to 1.4%). In conclusion, the results suggest that a constant and accurate follow-up should be reserved for all immunosuppressed patients as a crucial strategy to intercept lesions that have an increased potential to evolve into oral cancer.