Abstract Numerous studies have underscored the essential role of sunlight in vitamin D synthesis, while other studies have examined the association between dietary supplementation and vitamin D levels in different oncologic indications. In certain oncologic types, low levels of vitamin D correlate with a higher risk of cancer progression or poorer outcomes. On the contrary, the protective role of vitamin D remains ambiguous for some cancers. Given that the majority of cancer patients exhibit vitamin D deficiency or insufficiency, there have been suggestions to adopt supplementation strategies. However, vitamin D modulates and interacts with several molecular pathways. Therefore, it is crucial to contextualize the level and circumstances in which the action of vitamin D is observed. Distinct outcomes may emerge based on factors such as the method of assessing vitamin D levels, the size of the study populations, their genetic background, and the specific cancer type under investigation. In this article, we summarize some of the relevant studies examining the relationship between vitamin D levels and cancer. We further briefly outline the process of vitamin D synthesis and its effects on specific cellular pathways involved in cancer progression, highlighting essential considerations for future vitamin D assessments and supplementation approaches.