Higher levels of vitamin D are associated with decreasing risk of breast cancer, according to researchers at University of California San Diego School of Medicine who conducted an epidemiological study published in the June 15 online issue of PLOS ONE.
The study was conducted in collaboration with Creighton University, Medical University of South Carolina and GrassrootsHealth, an Encinitas-based nonprofit organization that promotes vitamin D research and its therapeutic benefits.
Researchers pooled data from two randomized clinical trials with 3,325 combined participants and a prospective study involving 1,713 participants to examine the association between risk of female breast cancer and a broad range of serum 25-hydroxyvitamin D (25(OH)D) concentrations, which was chosen as the marker because it is the main form of vitamin D in blood.
The data were collected between 2002 and 2017—all women were age 55 or older, and the average age was 63. Participants were free of cancer at enrollment and were followed for a mean period of four years. Vitamin D levels in blood were measured during study visits.
Over the course of the combined studies, 77 new cases of breast cancer were diagnosed for an age-adjusted incidence rate of 512 cases per 100,000 person-years.
Researchers identified the minimum healthy level of 25(OH)D in blood plasma to be 60 nanograms per milliliter, substantially higher than the 20 ng/ml recommended in 2010 by the Institute of Medicine, now the National Academy of Medicine, a health advisory group to the federal government. Some groups, such as GrassrootsHealth, have advocated higher minimums for health blood serum levels of vitamin D, as much as 50 ng/ml. The matter remains hotly debated.
“We found that participants with blood levels of 25(OH)D that were above 60 ng/ml had one-fifth the risk of breast cancer compared to those with less than 20 ng/ml,” said principal investigator and co-author Cedric Garland, adjunct professor in the UC San Diego Department of Family Medicine and Public Health. Risk of cancer appeared to decline with greater levels of serum vitamin D.
Multivariate regression was used to quantify the association between 25(OH)D and breast cancer risk, with the results adjusted for age, body mass index, cigarette smoking and intake of calcium supplements, said first author Sharon McDonnell, an epidemiologist and biostatistician for GrassrootsHealth. “Increasing vitamin D blood levels substantially above 20 ng/ml appears to be important for the prevention of breast cancer.”
Garland, who has previously studied connections between serum vitamin D levels and several types of cancer, said the study builds upon previous epidemiological research linking vitamin D deficiency to a higher risk of breast cancer. Epidemiological studies analyze the distribution and determinants of health and disease, but it has been argued that they do not necessarily prove cause-and-effect.
“This study was limited to postmenopausal breast cancer. Further research is needed on whether high 25(OH)D levels might prevent premenopausal breast cancer,” Garland said. The population was also mainly white women so further research is needed on other ethnic groups.
