The vitamin D levels in women when they are diagnosed with breast cancer may affect how long they will live, according to a new study from Belguim.
Women in the study who had the highest vitamin D levels (above 30 nanograms per millileter of blood) were about half as likely to die within five years of their diagnosis as women with lower vitamin D levels (below 30 ng/ml). And every 10 ng/ml increase in vitamin D levels at diagnosis was linked with a 20 percent reduction in women's risk of dying over the course of the study.
The link held even when researchers took into account factors known to influence women's cancer survival rates, such as body mass index and age.
Additionally, women in the study with higher vitamin D levels were more likely to have smaller tumors when they were diagnosed.
Researchers stressed that the study shows an association between the vitamin and survival rates, not a cause-and-effect link, and more work would be needed to confirm the findings. Researchers did not attempt to change women's vitamin D levels during the study; they took one measurement of vitamin D levels at the time of diagnosis.
The findings mean that physicians and oncologists are going to have to pay attention to vitamin D levels "more closely as their patients go through treatment,” said Luke Peppone, a clinical cancer researcher at the University of Rochester in New York, who was not involved in the study.
In the new study, researchers looked at nearly 1,800 women with breast cancer. By the study's end, 134 of the patients had died — 64 from breast cancer, 55 from other known causes and 15 from unknown causes.
The researchers noted that participants with higher BMIs tended to have lower vitamin D levels, and also that vitamin D levels were lower overall during the winter than during the summer. (Direct exposure to sunlight is a major provider of vitamin D.) The links between the vitamin and survival and tumor size held when these factors and others were taken into account.
One previous study linked vitamin D to breast cancer survival rate, Peppone said. The new study is impressive, he said, due to the large number of participants and the number of variables the researchers took into account.
In the study, the researchers also found a longer period between cancer remission and relapse for women with higher levels of vitamin D at their diagnosis, although this link was seen only in women who had experienced menopause.
Looking at the difference between premenopausal and postmenopausal women is important because 60 percent of cases of breast cancer occur in woman after menopause, Peppone said. Postmenopausal women also tend to be more likely to be deficient in vitamin D. This may because women's bodies use vitamin D in different ways after menopause, when estrogen levels drop.
“The effects of estrogen tend to be stronger than vitamin D, but when estrogen is depleted, vitamin D becomes more important,” Peppone said.
The study was published May 24 in the journal Carcinogenesis.
Pass it on: High levels of vitamin D may result in smaller breast cancer tumors and higher chance of surviving the disease.