Alone or in combination with other chemotherapeutic agents, a naturally occurring form of vitamin D2 inhibits the proliferation of breast and prostate cancer cells, according to a study recently published in the journal Anticancer Research.*
Adequate levels of vitamin D metabolites are required for the normal regulation of calcium and phosphate levels. Mounting epidemiological evidence has also shown that vitamin D affords significant protection against cancer. This is of particular consequence to elderly adults, in whom vitamin D synthesis is reduced, vitamin D deficiency is commonplace, and peak incidences of a variety of cancers occur.
While very low amounts of vitamin D are required to maintain calcium and phosphate homeostasis, the much higher doses of vitamin D needed for cancer prevention can result in hypercalcemia (excessive blood levels of calcium) and potentially lethal toxicity. The mechanism by which vitamin D inhibits tumor cell growth involves the vitamin D receptor, which together with vitamin D exerts negative feedback control on cancer cell proliferation and differentiation, and promotes cell death. Not surprisingly, scientists are now developing vitamin D analogs that have decreased calcium-mobilizing activity and therefore can be safely used in humans at these higher, effective doses.
In their study, researchers at Bone Care International in Middleton, WI, found that naturally occurring vitamin D2, which is derived from plants and has low calcemic activity, is effective alone or in combination with traditional chemotherapeutic agents in in-hibiting breast and prostate cancer cell lines in vitro. Vitamin D2 was found to potentiate the effect of therapeutic agents such as doxorubicin, cisplatin, busulfan, etoposide, 5-florouracil, carboplatin, and paclitaxel. Because toxicity limits these chemotherapeutic agents, the combined effect with vitamin D2 may enable dose reductions without loss of efficacy. Vitamin D2 also augments the effect of tamoxifen, a well-tolerated anti-estrogen used as adjuvant therapy in the prevention of breast cancer recurrence. The addition of vitamin D to the existing arsenal of anti-tumor agents may have enormous therapeutic potential.
—Linda M. Smith, RN