Decreasing 25‐hydroxy‐vitamin D levels account for portion of the effect of increasing body mass index on breast cancer mortality

Scope Increased body mass index ( BMI ) and decreased serum vitamin D are both known to be associated with increased mortality from breast cancer. However, vitamin D levels are lower in obese individuals in general. Recent studies have sought to determine whether serum vitamin D levels can account for some of the association between higher BMI and increased risk for breast cancer and found that low vitamin D levels in the overweight and obese account for up to 40% of the BMI ‐attributable risk of developing breast cancer. Methods and results Here we reviewed the literature to determine if a similar relationship exists between vitamin D, BMI , and breast cancer mortality. Utilizing previously reported independent associations of low vitamin D and high BMI to increases in breast cancer mortality, as well as the known decrement in vitamin D per unit increase in BMI , we estimated that low vitamin D levels may be responsible for roughly 16% of the increased mortality from breast cancer in overweight and obese patients. Conclusion Although this is a relatively small proportion of the effect of obesity, supplements to increase serum vitamin D levels may represent a way to reduce obesity‐associated disparities in breast cancer mortality.