Study Sees Link Between Vitamin D, Breast Cancer Prognosis
Article date: May 16, 2008
A new study suggests breast cancer patients might fare worse if they don't have enough vitamin D in their blood. However, experts warn more research is needed to know just how vitamin D might be linked to breast cancer, and they caution against going overboard with supplements.
The new work, by scientists at the University of Toronto, is scheduled to be presented later this month at the annual meeting of the American Society of Clinical Oncology. Lead researcher Pamela Goodwin, MD, discussed the findings at a press briefing Thursday. She is a professor of medicine at the University of Toronto and a senior investigator at the Samuel Lunenfeld Research Institute of Toronto's Mount Sinai Hospital.
Goodwin and her colleagues measured vitamin D levels in the blood of 512 newly diagnosed breast cancer patients (95% of them white) and tracked the progress of their disease over an average of about 12 years. About 38% of the women had vitamin D levels low enough to be considered "deficient" and 39% had levels that were "insufficient." Just 24% of the women in the study had "adequate" vitamin D levels.
Women with the lowest levels of vitamin D (deficient) had nearly double the risk of their disease progressing, and a 73% greater risk of death compared to women with adequate vitamin D. The findings were statistically significant, and were not affected by factors including age, weight, tumor stage or tumor grade.
But Goodwin cautions that her findings are preliminary and need to be repeated in other studies before firm conclusions about vitamin D and breast cancer can be drawn.
"In order to address whether [improving] vitamin D [status] might change outcomes in breast cancer, we would need a randomized trial," she said.
Other experts agree. Julie Gralow, MD, who moderated the press conference where the study was discussed, said, "We have no idea whether correcting vitamin D deficiency will in any way alter these outcomes." Gralow is associate professor of medical oncology at the University of Washington and the Fred Hutchinson Cancer research Center.
Too Much Vitamin D Might Be Harmful
Until more is known, Goodwin says she's recommending her patients take the amount of vitamin D currently recommended for bone health. The Institute of Medicine recommends 200 IU daily for women up to age 50, 400 IU for women 51-70, and 600 IU for women 71 and older.
"If women are considering taking vitamin D supplementation, particularly if it is higher than the levels recommended for bone health, we recommend they consider having their vitamin D levels checked to make sure they're at a healthy level," Goodwin said.
That's because high doses of vitamin D can be harmful. Too much can cause nausea, vomiting and weakness, and raise blood levels of calcium enough to cause mental confusion and heart rhythm abnormalities, as well as calcium deposits in the kidneys and other tissue. Goodwin also saw a suggestion in her study that too much vitamin D might also increase the risk of death in the women with breast cancer. However, her study was too small to be sure this finding wasn't due to chance, so this effect needs to be researched further.
Goodwin says her team is conducting additional studies of vitamin D in women with breast cancer. She expects results from one to be available by the end of this year.
In addition to availability in pill form, vitamin D is found in small amounts in foods like oily fish (salmon, tuna, mackerel). It is also added to milk, some cereals, and orange juice.
Sun exposure is another source: being in the sun causes the body to make vitamin D. Of course, sun exposure also raises the risk of melanoma and other types of skin cancer. For that reason, the American Cancer Society recommends a balanced diet, supplementation, and limiting sun exposure to small amounts as the preferred methods of obtaining vitamin D, says Marji McCullough, ScD, RD, strategic director of nutritional epidemiology at the American Cancer Society.
"If you are concerned about your vitamin D status and intake, talk with your physician and always be sure to tell him or her if you are taking any over the counter medications or supplements," McCullough says.
Citation: "Frequency of vitamin D (Vit D) deficiency at breast cancer (BC) diagnosis and association with risk of distant recurrence and death in a prospective cohort study of T1-3, N0-1, M0 BC." Presented at the 2008 annual meeting of the American Society of Clinical Oncology. First author: Pamela Goodwin, University of Toronto.
Reviewed by: Members of the ACS Medical Content Staff
ACS News Center stories are provided as a source of cancer-related news and are not intended to be used as press releases.
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