In their ER- breast cancer study, the researchers fed lean mice two doses of vitamin D - 15 or 20 K international units [IU] VD3 - from puberty onset onwards for 24 weeks. They found that the lower dose (15 K IU) of VD3 significantly reduced mammary tumor incidence as well as time for tumors to develop in lean mice, when compared to mice that were fed control diet. A higher dose (25K IU) was used in mice fed the obesity-inducing diet because vitamin D becomes trapped in fatty tissue and thus is reduced in the blood stream, Hilakivi-Clarke says. Obese mice destined to develop ER- cancer that were given vitamin D developed the highest incidence of breast cancer.

In their ER+ breast cancer, only the higher vitamin D dose (20K IU) was used. This dose significantly reduced breast tumor incidence in lean mice, compared to control or obese animals. Additionally, obese mice fed vitamin D developed fewer tumors than obese mice not supplemented with it, says Hilakivi-Clarke.

In both mouse models of breast cancer, obese mice developed insulin resistance, and vitamin D supplementation reversed it. However, vitamin D in lean mice tended to reduce insulin sensitivity in both mouse models, she says.

The researchers are currently studying possible mechanisms by which vitamin D may reverse obesity induced increase in breast cancer and insulin resistance, and preliminary results suggest vitamin D reverses the action of genes which promote inflammation, cell proliferation and survival, and this might involve epigenetic modifications.

Source: Georgetown University Medical Center