08/28/2026
A study published in The Journal of Steroid Biochemistry and Molecular Biology tested vitamin K2 (menaquinone-4) and the active form of vitamin D3, called calcitriol [1,25(OH)₂D3], on three triple-negative breast cancer cell lines: SUM159PT, Hs578T and MDA-MB-453. Vitamin K2 alone reduced the number of viable cancer cells in SUM159PT and MDA-MB-453 cells, but not in Hs578T cells. Active vitamin D3 also slowed cancer-cell growth by causing cells to stop or slow their normal cycle of division.
When researchers combined vitamin K2 with active vitamin D3, the combination produced stronger effects than either treatment alone in some of the cancer cells. In SUM159PT and Hs578T cells, the combination reduced viable cell numbers by about 40% after 96 hours. The combination also caused cell-cycle arrest in all three cell lines and affected stem-like cancer-cell features linked to tumor growth and recurrence. However, this was a laboratory cell study, not a human clinical trial, so it does not show that taking vitamin D3 and K2 supplements can treat breast cancer in people.
