Breast cancer patients with low levels of vitamin D when they're diagnosed have a higher risk of their cancer spreading and are more likely to die from the disease, according to new research from scientists in Toronto.
Women with vitamin D deficiency had almost twice the risk of the cancer spreading, and they were 73 percent more likely to die within 10 years.
The findings, announced Thursday by the American Society of Clinical Oncology, add to a growing body of evidence that vitamin D may play a role in preventing and perhaps limiting breast and other cancers.
"This study links vitamin D with the aggressiveness of disease," said University of Albany nutrition researcher JoEllen Walsh, an expert on vitamin D and breast cancer. "It suggests that your vitamin D status may affect how your disease progresses."
The human body produces vitamin D when exposed to sunshine; the chemical is also available in supplement form.
Researchers have known for more than two decades that vitamin D levels appear to affect the incidence of breast cancer. Many studies have found that low levels of vitamin D correlate with increased risk for cancers of the breast, prostate, pancreas, esophagus and colon.
The new study differed from previous work because it focused on what happened after patients were diagnosed.
"This is the first study to look at the impact of vitamin D on outcomes of breast cancer," said Dr. Pamela Goodwin, the study's lead author.
Goodwin, a cancer specialist at the University of Toronto, studied 512 women diagnosed with breast cancer between 1989 and 1995.
At the time of diagnosis, researchers took blood samples from the women. Just over 37 percent had low levels of the vitamin, just over 38 percent had moderately low levels and 24 percent had adequate levels.
Goodwin and her colleagues followed the women for 10 years. In 17 percent of the women with adequate levels of vitamin D, the cancer had spread. Fifteen percent of this group died. In 31 percent of the women with low levels, the cancer had spread; 26 percent of this group died. Women with moderately low levels of vitamin D fell in between the two groups.
Goodwin noted that vitamin D is not a panacea. "You still need to have your mammograms and your breast exams," she said.
The findings will be officially presented next month at the annual conference of the American Society of Clinical Oncology.
It is not clear how vitamin D prevents or controls cancer. Almost every cell in the body has receptors that are activated by the chemical. Scientists suspect that the substance may work by controlling growth, ensuring that cells don't proliferate randomly, a process that can devolve into cancer.
In recent years, vitamin D has become a golden child of the supplement world. Researchers have found evidence suggesting it helps prevent or treat a range of diseases, including diabetes, multiple sclerosis, rheumatoid arthritis, muscle pain, depression, heart disease and stroke.
At Your Prescription for Health, an Owings Mills pharmacy that sells supplements, vitamin D is a big seller, according to pharmacist and co-owner Brian Sanderoff. He's not surprised by the latest study.
"We've been preaching about vitamin D for years," he said. "It confirms what we already knew."