The researchers believe vitamin D shows promise as an effective treatment for bladder cancer, and may also play a role in prevention of the disease.

Lead author Dr. Badrinath R. Konety and colleagues presented their findings this week at the 95th Annual Meeting of the American Urological Association in Atlanta, Georgia.

"While there is still more research to be done," Konety tells cancerfacts.com, "We are very excited," Konety says.

Calcitriol (1, 25 dihydroxycholecalciferol), the primary physiologically active form of vitamin D, was found to significantly slow growth and stimulate apoptosis (programmed cell death) in bladder cancer cells in a dose-dependant manner. Administration of calcitriol also reduced the incidence of new tumors (55% versus 66%) in rats with induced bladder cancer. The tumors that did form in calcitriol treated animals were less invasive (20% versus 50%) and more likely to be single focus than those in control animals.

High doses of vitamin D administered throughout the body can produce a serious side effect called hypercalcemia, or high blood calcium. Even though the vitamin has exhibited strong antiproliferative effects in a number of other cell types, including prostate cancer, this intolerable side effect has limited vitamin D's use as a therapy.

Bladder cancer, however, has the unique feature of being accessible through the urethra in a procedure called intravesical (directly into the bladder) administration. Injection of calcitriol through the urethra not only evades the toxicity of systemic administration, but also allows for a greater dosage range to yield maximum benefit.

Animals treated intravesically with calcitriol were free from vitamin D related side effects, experiencing neither significant weight loss nor a fluctuation in serum calcium levels.

Konety and his team are now studying the protective effects of vitamin D on transgenic mice -- mice whose specific genetic alterations render them destined to develop bladder cancer. They hope to prevent the onset of cancer in these animals with dietary or low pharmacologic doses of vitamin D. That research is under way.

In the mean time, Konety urges patients to discuss any plans of taking vitamin supplements with their physicians. "The toxicity of vitamin D can be very high," Konety says, "and patients loading up on it in hopes of treating their cancer may unknowingly interfere with the effect of other medications or therapies."

The American Cancer Society estimates that in 2000 there will be about 53,200 new cases of bladder cancer diagnosed in the United States (about 38,300 men and 14,900 women), and 12,200 deaths from the disease (about 8,100 men and 4,100 women).