Vitamin D and breast cancer risk

ORLANDO, Fla., April 4 (UPI) -- Vitamin D can decrease or increase the risk of breast cancer development and insulin resistance, U.S. researchers said.

Lead investigator Leena Hilakivi-Clarke, a professor at the Georgetown Lombardi Comprehensive Cancer Center, a part of Georgetown University Medical Center, found vitamin D significantly reduced development of estrogen receptor-positive breast cancer in lean and obese mice, but there was no beneficial effect in estrogen receptor-negative cancer.

The study found the obese mice destined to develop ER negative breast cancer were worse off than lean ER negative mice if they were given vitamin D in their diet, Hilakivi-Clarke said.

"Use of vitamin D supplementation is clearly tricky," Hilakivi-Clarke said in a statement. "In the many studies that have been done studying the effect of vitamin D in different cancer types, there is no straight link between use and benefit."

The findings, presented at the American Association for Cancer Research 102nd annual meeting in Orlando, Fla., said vitamin D reversed insulin resistance -- a risk factor for diabetes -- in obese mice, no matter which breast cancer subtype they later developed. However, there was no evidence that vitamin D increased insulin sensitivity.

"This is not a vitamin that should be taken lightly," Hilakivi-Clarke cautions. "People need sufficient amounts because it has beneficial effects for overall health that have nothing to do with preventing cancer. But for those who want to boost their use of vitamin D, it is important that they have their individual levels tested by a physician, and that they discuss their desire to use supplements."