Researchers from Columbia University have reported that vitamin D deficiency is present in 74% of women with premenopausal early-stage breast cancer and that this deficiency is not corrected with daily supplementation of 400 IU/day. The details of this study were reported in the May 1, 2009 issue of the Journal of Clinical Oncology.[1]

There is increasing evidence that high levels of vitamin D are associated with a lower incidence of breast cancer. There is also evidence that the standard recommendations of 400 IU/day are too low to make an impact on breast cancer prevention. Most recent studies suggest that 1000-1500 IU/day of vitamin D is required for cancer prevention. Researchers from Toronto, Canada, have reported that women with early breast cancer who have low blood levels of vitamin D have a worse outcome than those with adequate levels of vitamin D. Less than one-quarter of women in this study had adequate vitamin D levels upon diagnosis of breast cancer. Women with low levels of vitamin D had a 94% increased risk of cancer spread compared with those with adequate vitamin D levels. Women with low levels of vitamin D had a 73% increased risk of death compared with those with adequate vitamin D levels.

In the current study, researchers evaluated vitamin D levels in 103 pre-menopausal women with early-stage breast cancer. Patients in this study were all receiving adjuvant chemotherapy and were participating in a one-year trial of Zometa® (zoledronate). All women were prescribed 400 IU/day of vitamin D and 1,000 mg/day of calcium carbonate. A serum 25-hydroxyvitamin D (25-OHD) level of 20 ng/mL was defined as deficiency, a level between 20 and 29 ng/mL was defined as insufficiency, and a level of 30 ng/mL was defined as adequate. Other studies have suggested that the optimal level of 25-OHD is 75 ng/mL. By these criteria, 74% of women were vitamin D deficient at baseline. However, 80% of African Americans and 84% of Hispanics were vitamin D deficient at baseline. After one year of supplementation, only 15% of White and Hispanic women achieved sufficient levels of 25-OHD and no African-American woman achieved this level. Chemotherapy and bisphosphonate use did not alter these results.

Comments: These data suggest that vitamin D deficiency in women is widespread and greater in African-American and Hispanic women. Several studies have suggested that the recommended daily dose of 400 IU/day is too low, especially during winter months. Currently, 1000 IU/day is recommended, but even this may be too low; some researchers have recommended 1500-2000 IU/day. Another factor that has to be considered is that some studies have suggested that up to 40% of women prescribed vitamin D supplements are non-compliant, further complicating studies of the efficacy of a given dose of vitamin.

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