Common sources of vitamin D include sun exposure, fatty fish oils, vitamin supplements, and fortified milks and cereals. While the mechanisms for how vitamin D influences breast cancer outcomes are not well understood, researchers believe it may be related to its role in promoting normal mammary-cell development, and inhibiting the reproduction of and promoting the death of cancer cells.
"We found that women with the highest levels of vitamin D levels had about a 30 percent better likelihood of survival than women with the lowest levels of vitamin D," said Lawrence H. Kushi, ScD, research scientist with the Kaiser Permanente Northern California Division of Research and principal investigator of Kaiser Permanente's Pathways study of breast cancer survivorship. The current study included 1,666 Pathways study members who provided samples between 2006 and 2013.
With funding from the National Cancer Institute, the Pathways study began enrolling Kaiser Permanente members in Northern California who had a diagnosis of invasive breast cancer in 2006. Participants provided blood samples within two months of diagnosis and answered questions about diet, lifestyle and other risk factors, with follow-ups at six months and at two, four, six and eight years.
"With the extremely rich data sources from a large sample size, we were able to prospectively analyze three major breast cancer outcomes — recurrence, second primary cancer and death," said Song Yao, PhD, associate professor of oncology at Roswell Park Cancer Institute and the study's lead author. The institute, located in Buffalo, NY, is a partner in the Pathways study.
"We were also able to adjust for multiple possible contributing factors that could influence vitamin D levels," Yao said, "such as age, obesity, race and ethnicity, socioeconomic status, and several tumor characteristics that are known to influence breast cancer outcomes — to ensure that the effects we observed were independent of these factors."
In addition to lower overall mortality among all breast cancer survivors studied, the researchers found even stronger associations among premenopausal women in the highest third of vitamin D levels for breast-cancer-specific (63 percent better), recurrence-free (48 percent better) and invasive-disease-free survival (42 percent better), during a median follow up of seven years.
Although the study did not examine the effects of vitamin D intake from foods versus supplements, Kushi noted that it supports the recommended daily levels of vitamin D (600 IU for those 1 to 70 years old and pregnant or breastfeeding women, and 800 IU for those over 71 years old).
"The more we know about vitamin D, the more we understand that it may play a key role in cancer prevention and prognosis," Kushi said. "This study adds to the evidence that vitamin D is an important nutrient."
The National Cancer Institute recently awarded a five-year, $10 million grant to Kaiser Permanente and Roswell Park Cancer Institute, co-led by Kushi and Christine Ambrosone, PhD, senior vice president for population sciences at Roswell Park and a key collaborator on the vitamin D research. The new funding will allow researchers to continue following Pathways participants, establish a biorepository of tumor specimens, conduct germline genetic assessments, and obtain more information about the characteristics of neighborhoods in which the women reside.
This study is part of Kaiser Permanente's ongoing efforts to understand the complexities associated with breast cancer survival and outcomes. For example, last year Kaiser Permanente researchers found a lower risk of recurrence in patients who breastfed and among those with specific HER2 positive tumors. In addition, in two separate studies published in 2013 researchers found that breast cancer survivors with strong social networks had a lower risk of mortality, while those who consumed high-fat dairy products had a higher mortality risk.
In addition to Kushi, Yao and Ambrosone, co-authors were Marilyn L. Kwan, PhD, Isaac J. Ergas, MPH, Janise M. Roh, MPH, MSW, and Charles P. Quesenberry, Jr., PhD, of the Kaiser Permanente Northern California Division of Research; Ting-Yuan (David) Cheng, PhD, Chi-Chen Hong, PhD, Susan E. McCann, PhD, RD, Li Tang, MD, PhD, Warren Davis, PhD, and Song Liu, PhD, of Roswell Park Cancer Institute, Buffalo, NY; and Marion M. Lee, PhD, MPH, of University of California, San Francisco.
About the Kaiser Permanente Division of Research
The Kaiser Permanente Division of Research conducts, publishes and disseminates epidemiologic and health services research to improve the health and medical care of Kaiser Permanente members and society at large. It seeks to understand the determinants of illness and well-being, and to improve the quality and cost-effectiveness of health care. Currently, DOR's 550-plus staff is working on more than 350 epidemiological and health services research projects. For more information, visit www.dor.kaiser.org or follow us @KPDOR.
About Roswell Park Cancer Institute
The mission of Roswell Park Cancer Institute (RPCI) is to understand, prevent and cure cancer. Founded in 1898, RPCI is one of the first cancer centers in the country to be named a National Cancer Institute-designated comprehensive cancer center and remains the only facility with this designation in Upstate New York. The Institute is a member of the prestigious National Comprehensive Cancer Network, an alliance of the nation's leading cancer centers; maintains affiliate sites; and is a partner in national and international collaborative programs. For more information, visit www.roswellpark.org, call 1-877-ASK-RPCI (1-877-275-7724) or email email@example.com. Follow Roswell Park on Facebook and Twitter.
About Kaiser Permanente
Kaiser Permanente is committed to helping shape the future of health care. We are recognized as one of America's leading health care providers and not-for-profit health plans. Founded in 1945, Kaiser Permanente has a mission to provide high-quality, affordable health care services and to improve the health of our members and the communities we serve. We currently serve more than 10.6 million members in eight states and the District of Columbia. Care for members and patients is focused on their total health and guided by their personal physicians, specialists and team of caregivers. Our expert and caring medical teams are empowered and supported by industry-leading technology advances and tools for health promotion, disease prevention, state-of-the-art care delivery and world-class chronic disease management. Kaiser Permanente is dedicated to care innovations, clinical research, health education and the support of community health. For more information, go to: kp.org/share.
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SOURCE Kaiser Permanente