There are many questions regarding whether supplementing Vitamin D can cause a decrease in cancer incidence and whether you should take this vitamin. One normally produces Vitamin D when exposed to sunlight, but we can also find it in foods such as fish, mushrooms, milk, and some cereals.

Vitamin D can downregulate growth hormones and suppress proliferation in many cancers. Vitamin D receptors are widely expressed throughout the body, and experimental evidence suggests that vitamin D has antineoplastic activity. Vitamin D binding to its receptor results in transcriptional activation and repression of target genes producing apoptosis, antiproliferative effects, autophagic cell death and angiogenesis, and immunomodulatory effects that contribute to reduced metastatic disease and fatal cancer.

It has been shown that vitamin D is able not only to potentiate the effects of traditional cancer therapy as gemcitabine, cisplatin, doxorubicin, and proton therapy but can even contribute to overcoming the molecular mechanisms of drug resistance; it can act at various levels through the regulation of growth of cancer stem cells and the epithelial-mesenchymal transition and the modulation of miRNA gene expression.

This antitumor action is probably because it influences intracellular calcium oscillations capable of influencing cell mechanisms of growth and apoptosis. In recent years, vitamin D has modulated the inflammatory state of the tumor microenvironment by affecting immunological infiltrations.

Harvard researchers set out in 2011 a large study with 25,871 people with randomized vitamin D supplementation. The results showed that the rate of fatal or metastatic cancer was 17% lower in those taking vitamin D supplements and 38% in people with a healthy weight.

Although it has been proven that Vitamin D3 can reduce the risk of advanced cancer, metastasis, and fatal cancer, it is not associated with cancer prevention.

References: Mariarosaria Negri,Annalisa Gentile, Cristina de Angelis, Tatiana Montò,Roberta Patalano, Annamaria Colao, Rosario Pivonello, and Claudia Pivonello,  2020 Jun 17, Vitamin D-Induced Molecular Mechanisms to Potentiate Cancer Therapy and to Reverse Drug-Resistance in Cancer Cells,,activation%20of%20different%20molecular%20pathways.,leading%20to%20reduced%20cancer%20mortality.&text=Higher%20serum%2025%2Dhydroxyvitamin%20D,longer%20survival%20in%20cancer%20patients.