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.
Keeping an Eye on Vitamin D Levels
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.
A 2006 study by researchers at the University of California at San Diego, involving more than 120,000 women, showed that those women with the highest blood levels of vitamin D had a 50 percent reduced risk of breast cancer. Their study was published in the journal Nutrition Reviews.
However, a 1999 study by researchers at the University of Miami and the Northern California Cancer Center in Union City, Calif., found that vitamin D status had no effect on breast cancer mortality. Their study was published in the Journal of the National Cancer Institute.
Despite the conflicting evidence, some experts still recommend that all their patients supplement their vitamin D.
"All my patients are on Vitamin D," said Stefan Glück, clinical director of the Braman Family Breast Cancer Institute and UMSylvester Comprehensive Cancer Center at the University of Miami's Miller School of Medicine. "They should [take one vitamin D supplement] per day, or prior to sun exposure, put your sunscreen on 10 minutes after you are exposed."
According to Gluck, those 10 unprotected minutes in the sun give you about 12,000 IUs of vitamin D -- about 12 times the amount you get from taking one vitamin D supplement.
Still, some experts said they refrain from recommending that their cancer patients begin vitamin D supplementation as a preventive measure because of past conflicting evidence on the benefit of such supplementation.
"On the basis of this study, I would not recommend vitamin D supplementation," said Tim Byers, professor in the Department of Preventive Medicine and Biometrics and deputy director at the University of Colorado's Cancer Center. "There have been far too many examples in the past where preliminary studies of this type led to recommendations for supplementation that later we found to be either not helpful or harmful."
Natural Way to Get Vitamin D: Sun's Rays
Past research has indicated that oversupplementing your vitamin D can be toxic, leading to symptoms such as nausea, vomiting, poor appetite, constipation, weakness and weight loss. More seriously, it can also raise blood levels of calcium, causing kidney stones or even heart rhythm abnormalities.
Vitamin D is found in salmon and other oily fish, and is routinely added to milk, but diet accounts for very little of the vitamin D nutrient that enters into the bloodstream. Most people get their vitamin D from dietary supplements. However, the simplest way to get your daily dose of vitamin D is from the sun's ultraviolet rays, which naturally trigger vitamin D synthesis.
Vitamin D is essential for promoting calcium absorption in the stomach and maintaining bone health, immune function and reduction of inflammation.
Preliminary, but Promising
Overall, many cancer experts said that they are encouraged by the results of this study, though remain cautious in making any specific recommendations to their patients on supplementing their vitamin D as a method of preventing cancer or improving cancer outcomes.
"I agree with researchers for putting study in proper light -- that it's a preliminary study and needs to be confirmed by more research, and doctors should not make specific recommendations to women with breast cancer based on this study," said Len Lichtenfeld, deputy chief medical officer of the American Cancer Society.
The American Cancer Society currently recommends that people should be taking 1,000 international units of vitamin D every day -- or one vitamin D supplement pill daily. However, without more research on the specific impact that vitamin D has on cancer prevention and cancer outcomes, many experts said they are unable to provide a one-size-fits-all recommendation to cancer patients on how they can use this vitamin to improve their chances of survival.
"We need to get arms around vitamin D and its impact on health," Lichtenfeld said. "We need to figure out how much should we be taking, how and if it reduces cancer risk or changes the course of cancer once it is diagnosed.
"These are very important questions, and we need to get the appropriate people together to make recommendations on what we should be telling our patients about this," he said.