Vitamin D binds receptors on breast epithelium to regulate cell cycle, promote differentiation, protect against cellular DNA damage, regulate cytokines, activate immune cells and suppress inflammation.
The current analysis investigated the relationship between serum 25(OH)D and breast cancer across a wide range of 25(OH)D concentrations in women aged 55 and older.
The analysis pooled data from three studies. The 2007 and 2017 Lappe cohorts were each 4-year trials of vitamin D and calcium supplementation in women aged 55 and older, and cancer-free at enrolment, in Eastern Nebraska.
The Grassroots Health cohort was a 2-year study of men and women worldwide, but only data from women aged 55 and older and cancer-free at enrolment were included in the current analysis.
The pooled analysis from the 3 cohorts included a total of 5038 women. During a median follow-up of 4 years, 77 women were diagnosed with breast cancer.
Breast cancer incidence rates were 82% lower for women with serum vitamin D >60 ng/mL (150 nmol/L) vs <20 ng/mL (50 nmol/L); rate ratio = 0.18; 95% CI, 0.04-0.62.
Kaplan-Meier curves were significantly different for women with different vitamin D concentrations: the highest proportion of women to be breast-cancer free after 4 years were in the >60 ng/mL group (99.3%), and the lowest proportion of breast-cancer free were in the <20 ng/mL group (96.8%).
Multivariate Cox regression showed that women with 25(OH)D concentrations >60 ng/mL had an 80% lower risk of breast cancer than women with concentrations <20 ng/mL (HR=0.20; p=0.03).
The National Academy of Medicine currently recommends a serum vitamin D level of 20 ng/mL (50 nmol/L), but this is based on its relationship to bone health.
The current analysis suggests that higher concentrations confer greater protection against breast cancer.
This analysis showed a consistent decrease in breast cancer risk as serum 25(OH)D concentrations increased, with no evidence of increased risk at higher levels. The authors of this study conclude that vitamin D is a modifiable risk factor for breast cancer.
