Higher Vitamin D Levels Linked to Better Breast Cancer Outcomes

11 Nov 2016 --- Women with higher vitamin D levels in their blood following a breast cancer diagnosis had significantly better long-term outcomes, according to new research from Kaiser Permanente and Roswell Park Cancer Institute, published online in JAMA Oncology.

Vitamin D is best known for its role in maintaining healthy bones, yet a deficiency of the mineral has been associated with the risk for several cancers.

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.

“We were also able to adjust for multiple possible contributing factors that could influence vitamin D levels,” Yao explained, “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.”