Women who have higher levels of vitamin D when they're diagnosed with breast cancer appear to have smaller tumors, researchers said here.
In a retrospective study, lower vitamin D levels were significantly associated with larger tumor size (P=0.0063), Barbara Brouwers, PhD, of the University of Leuven in Belgium, reported during a poster session at the San Antonio Breast Cancer Symposium here.
"Lower vitamin D levels were correlated with much bigger tumors," she told MedPage Today. "We also saw that higher vitamin D levels were associated with better outcomes, but it wasn't significant."
Brouwers explained that many studies have shown that vitamin D status is important in many chronic illnesses, and some have even shown low vitamin D levels to be a risk factor for breast cancer, as well as a predictor of outcomes.
Yet it's difficult to interpret its specific role given the many confounding factors known to influence serum concentrations, such as dietary intake, seasonal variation, and weight.
Also, genetic variants regarding vitamin D metabolism could influence risk, she added.