Researchers looked at more than 5 000 women, 55 and older, and found that those with vitamin D blood levels of 60 nanograms per millilitre (ng/mL) or more had an 80% lower risk for breast cancer than those with levels of 20 ng/mL or less.
The researchers also found that among women with vitamin D blood levels between 20 and 60 ng/mL, the higher their level, the lower their risk of breast cancer.
But the study did not prove that higher vitamin D levels prevent breast cancer, just that there was an association.
Data from clinical trials conducted at Creighton University in Omaha, Nebraska, and from GrassrootsHealth, a California-based nonprofit, were included in the study.
Different levels for bone health
“This study provides strong support that vitamin D plays an important role in breast cancer prevention,” said principal investigator Joan Lappe. She is a professor of nursing at Creighton.
“It also demonstrates that blood levels of vitamin D for breast cancer prevention need to be higher than currently recommended levels for bone health,” Lappe said in a university news release.
The study was published online recently in the journal PLoS One.
A vitamin D blood level of 20 ng/mL or above is adequate for bone health, according to the National Academy of Sciences.
Carole Baggerly, director of GrassrootsHealth, said, “With roughly an 80% reduction in the incidence of breast cancer, getting a vitamin D blood level to 60 ng/mL becomes the first priority for cancer prevention.”
According to Baggerly, “Nutrition and lifestyle factors are certainly important for overall health, but they can’t replace the value of vitamin D level. The safety of this level has been demonstrated within this study as well as others.”
According to the Cancer Association of South Africa (CANSA), in 2013 breast cancer accounted for 0.7% of South African deaths. NGO Marie Stopes notes that, spanning all race groups, one in 31 women is diagnosed with breast cancer in their lifetime.