By David Liu, PHD

Thursday April 5, 2012 (foodconsumer.org) -- If you are a frequent visitor to foodconsumer.org, you may already know that studies suggest that high doses of vitamin D may help prevent or even treat breast cancer.

Early studies found the hormonally active vitamin D metabolite called 1,25-dyhydroxyvitamin D3 or [1,25(OH)2D3 or calcitriol possesses anticancer actions in animals with breast cancer and prostate cancer.

A new study led by Srilatha Swami  of Stanford University School of Medicine in Stanford, California and colleagues now suggests women may not have to receive the prescription form of vitamin D, [1,25(OH)2D3), to cure your breast cancer. (This potent anticancer drug may not have been used clinically?). 

Instead, the researchers found taking high doses of vitamin D, which is hormonally inactive, may deliver the same efficacy in treating breast cancer, at least in mice.  Even better, the inactive vitamin D has no side effects seen in mice treated with active vitamin D, [1,25(OH)2D3].

The study was published online March 27, 2012 in the journal Endocrinology.

Inactive vitamin D can be converted into active vitamin D, 2,25(OH)2D3 through an enzyme called 1alpha-hydroxylase in the kidney.  But it can also be formed in other organs or tissues.

The researchers found significant tumor shrinkage in more than 50 percent of mice bearing MCF-7 breast cancer xenografts that were fed a diet supplemented with vitamin D3 in a dose of 5000 IU/kg, compared to a control diet which contained only 1000 IU/kg.

The efficacy was the same as that seen in mice that were given administered calcitriol in doses of 0.025, 0.05 or 0.1 micrograms per mouse, three times a week.

Both treatments, high doses of inactive vitamin D, which is found in most vitamin D supplements, and administered active vitamin D, were equally effective in inhibiting PC-3 prostate cancer xenografts growth, but less effective in treating MCF-7 tumors.

One side effect which is associated with use of high doses of vitamin D for a long period was an increase in serum calcium levels.  This was observed in mice receiving the administered active vitamin D, but not in mice fed dietary inactive vitamin D.

In the study, use of calcitriol at 0.05 μg and 0.1 μg was found to cause modest but statistically significant increases in serum calcium levels while dietary vitamin D3 in doses of 5000 IU/kg did not increase serum calcium.

Evidence from the current study also shows that dietary vitamin D3 increased circulating or serum 1,25-dihydroxyvitamin D levels, but did not change CYP27B1 mRNA in the kidney, but in the tumors.

Additionally, both calcitriol and dietary vitamin D were found equally effective in suppressing the synthesis of estrogen, which is known to promote breast cancer.

The researchers said the findings suggest that dietary vitamin D may be employed to prevent or treat breast cancer.

Vitamin D deficiency has been associated with increased risk of at least 17 types of cancer including breast cancer, which is expected to be found in more than 200,000 women in the United States in 2012, according to the National Cancer Institute.