Despite recent data indicating that vitamin D may have a preventive effect against cancer, 74% of premenopausal women with early-stage breast cancer are deficient in the vitamin, according to the results of a study published in the Journal of Clinical Oncology. Furthermore, daily supplementation of 400 IU of vitamin D does not appear to correct the deficiency.
Vitamin D is synthesized in the body through exposure to sunlight and may also be obtained through diet or supplements. The protective benefits of vitamin D are not understood; however, the association between levels of vitamin D and risk for certain types of cancer continues to be evaluated.
There is increasing evidence that high levels of vitamin D are associated with a lower incidence of breast cancer. Researchers from Toronto, Canada, have reported that women with early breast cancer who have low blood levels of vitamin D have worse outcomes than those with adequate levels of vitamin D.
In a recent study, researchers evaluated vitamin D levels in 103 premenopausal women with Stages I-III breast cancer. All patients in the study were receiving adjuvant chemotherapy and were participating in a one-year clinical trial of Zometa® (zoledronate). The women received 400 IU/day of vitamin D and 1,000 mg/day of calcium carbonate; their blood was collected and analyzed for vitamin D levels at baseline, six months, and 12 months.
Vitamin D sufficiency was defined as 30 ng/mL or greater; insufficiency as 20-29 ng/mL, and deficiency as below 20 ng/mL. At baseline, 74% of women in the study were vitamin D deficient. Vitamin D deficiency was more common in African-American (80%) and Hispanic (84%) women than in White women (66%). After one year of supplementation, only 15% of White and Hispanic women achieved sufficient levels of vitamin D and no African-American women achieved this level.
The researchers concluded that vitamin D deficiency is common among women with breast cancer and the current recommended supplementation dosage is too low to increase vitamin D levels. Optimal dosing of vitamin D has yet to be determined, but some studies have indicated that 1000-1500 IU/day is required for cancer prevention.
 Crew KD, Shane E, Cremers S, et al. High prevalence of vitamin D deficiency despite supplementation in premenopausal women with breast cancer undergoing adjuvant chemotherapy. Journal of Clinical Oncology. 2009; 27: 2151-2156.
 Goodwin P, Ennis M, Pritchard K, Koo J, Hood N. Vitamin D is common at breast cancer diagnosis and is associated with a significantly higher risk of distant recurrence and death in a prospective cohort study of T1-3, N0-1, M0 BC. Early Release Proceedings from the 2008 American Society of Clinical Oncology. Abstract #511.