The compounds are "promising" for preventing prostate cancers that are sensitive to male sex hormones (androgen), write the researchers.
The study was done on male mice, not people. More work is needed to probe the compound's cancer-fighting potential.
Focusing on Vitamin D
People can get vitamin D from dairy products or supplements. Their bodies also make vitamin D when sufficiently exposed to sunlight. It is necessary for normal bone development.
Calcitriol has "potent anti-tumor activities," write the researchers, who included Adebusola Alagbala of the Roswell Park Cancer Institute in Buffalo, N.Y.
But the story isn't quite that simple.
Calcitriol increases the level of calcium in the blood. However, it may raise the blood's calcium level too high, which could lead to other dangers such as abnormal heart rhythms, muscle weakness, and confusion. The effect of hypercalcemia (elevated calcium levels) from the calcitriol limits its ability to be used to fight cancer, write Alagbala and colleagues.
So scientists have made versions of calcitriol that don't affect the blood's calcium levels as much.
Alagbala's team studied calcitriol and a lab-made version of calcitriol (called "QW") in mice.
Their results were presented at Frontiers in Cancer Prevention Research, a meeting held by the American Association for Cancer Research.
Thwarting Prostate Cancer in Mice
The mice were genetically programmed to develop prostate cancer.
The mice got calcitriol, QW, or a fake drug three times weekly for 14 weeks. Calcitriol and QW both slowed the progression of prostate cancer in the mice, the researchers report.
Then, calcitriol was given to mice for a longer time -- up to 30 weeks. Calcitriol "markedly reduced tumor burden over time," write the researchers.
However, some mice experienced toxic side effects from calcitriol. Those side effects aren't detailed in the report.
A group of castrated mice was given calcitriol, QW, or the fake drug for 12 weeks.
In those mice, vitamin D compounds didn't slow, prevent, or affect prostate cancer development.
Castrated mice don't make sex hormones. That may mean that vitamin D compounds work against androgen-sensitive prostate cancers, write the researchers.