Principal investigator Cedric Garland, professor at the University of California, San Diego, said several previous studies showed low serum levels of vitamin D were associated with a higher risk of premenopausal breast cancer.
"While the mechanisms by which vitamin D could prevent breast cancer are not fully understood, this study suggests that the association with low vitamin D in the blood is strongest late in the development of the cancer," Garland said in a statement.
The study drew upon 9 million blood serum specimens frozen by the Department of Defense Serum Repository for routine disease surveillance. The researchers thawed and analyzed pre-diagnostic samples of serum from 1,200 women whose blood was drawn in the same time frame -- samples from 600 women who later developed breast cancer, and from 600 women who remained healthy.
The study, published online in advance of the print edition of the journal Cancer Causes and Control, pointed to the possibility of a relevant window of time for cancer prevention in the last three months preceding tumor diagnosis -- a time physiologically critical to the growth of the tumor.
Garland said this is likely to be the point at which the tumor might be most actively recruiting blood vessels required for tumor growth.
"Based on these data, further investigation of the role of vitamin D in reducing incidence of premenopausal breast cancer, particularly during the late phases of its development, is warranted," Garland said.