Women with early-stage breast cancer have higher levels of vitamin D and lower levels of parathyroid hormone in their bloodstream than women with advanced or metastatic breast cancer, according to an observational study published in the Journal of Clinical Pathology.
Past epidemiologic studies have suggested a link between higher vitamin D levels through exposure to sunlight and reduced prevalence of breast cancer. Previous research also has demonstrated that vitamin D levels are higher in healthy women, compared with those with primary breast cancer, and levels decrease with progression of bone metastases.
In the current study, researchers prospectively evaluated 279 white women with invasive breast cancer, including 204 with early-stage cancer and 75 with locally advanced or metastatic disease.
The investigators found significantly higher levels of 25 hydroxyvitamin D in the blood serum of women with early-stage breast cancer. The mean vitamin D level was 57 nmol/L in those women, compared with 46 nmol/L in the women with advanced breast cancer.
Parathyroid hormone levels also were significantly lower in the women with early-stage breast cancer: 3.91 pmol/L, compared with 5.06 pmol/L in the women with advanced or metastatic breast cancer.
The researchers, led by Dr. Carlo Palmieri of Imperial College in London, wrote that the study does not determine whether the reduced vitamin D levels helped contribute to advanced cancer or whether it is a consequence of “reduced dietary intake or altered synthesis in the skin due to reduced sun exposure” in those patients with more advanced disease.
“In summary, these findings lend support to the hypothesis that vitamin D has a role in the pathogenesis and progression of breast cancer,” the authors said (J. Clin. Pathol. 2006 Oct. 17 [Epub doi: 10.1136/jcp.2006.042747]).
Animal studies have shown that vitamin D can inhibit growth of breast cancer cell lines and development of carcinogen-induced mammary tumors, as well as by promotion of apoptosis, although the exact mechanisms are not clear, they noted.