Vitamin D deficiencies have long been associated with disease, but new research suggests that low levels of vitamin D in women with breast cancer can lead to more aggressive forms of the disease, and even death.
Researchers at the University of Toronto studied the correlation between vitamin D levels in the blood, the rate of breast cancer metastases -- the incidence of having the cancer spread -- and the overall survival rates of 512 women who were diagnosed with breast cancer between 1989 and 1995. The women were followed until 2006.
Researchers found for the first time that women who were vitamin D deficient at the time of their breast cancer diagnosis were 94 percent more likely to have their cancer spread, and 73 percent more likely to die from their cancer, compared with women who were not vitamin D deficient.
Moreover, researchers found that about 75 percent of the women had a vitamin D deficiency at the time of their diagnosis.
Pamela Goodwin, lead study investigator and professor of medicine at the University of Toronto, said that breast cancer experts have only a preliminary understanding of why this vitamin would have such a profound impact on the breast cancer survival rates.
"Previous research has shown that breast cancer cells have vitamin D receptors, and we can slow down the growth of these cancer cells and take away some of their aggressiveness with vitamin D," Goodwin explained.
Despite this clear biologic basis for concluding that vitamin D has an impact on breast cancer, Goodwin cautioned that we do not have evidence that taking vitamin D will prevent breast cancer, and she would not encourage cancer-free women to begin taking the vitamin simply as a preventive measure.
Julie Gralow, oncology specialist and associate professor in the Medical Oncology Division of the University of Washington in Seattle, said that while she would not recommend that women without breast cancer supplement their vitamin D intake as a preventive measure, she would encourage all women to measure their vitamin D levels and ensure that they do not suffer from a deficiency of this nutrient.
Today, testing for vitamin D levels is as simple as drawing blood from a patient. A specific blood test known as the 25-hydroxy vitamin D test can quickly and accurately determine whether a patient is vitamin D deficient.
Now that such tests are available, Gralow said that women should be encouraged to stay on top of their vitamin D levels, get screened for their vitamin D levels and safely correct any vitamin D deficiencies with the help of a doctor.
"I wouldn't tell someone not to correct a vitamin D deficiency if they had one," Gralow said. "Finally, in the last year or two, we've developed reliable tests to determine vitamin D levels. There is caution for why we might correct vitamin D levels, such as bone health and calcium absorption, but I don't think if we do it safely that we will create many problems in vitamin D deficiencies."
Until now, only preclinical studies have suggested a link between vitamin D and cancer. Animal studies, as well as epidemiologic data, have suggested that vitamin D deficiencies could affect cancer risk. Moreover, experts have strong biological evidence that vitamin D plays a role in the prevention of colon, prostate and breast cancers.
However, the findings of previous studies on vitamin D and cancer risk have proved conflicting.