Vitamin D and breast cancer: interpreting current evidence

Abstract

Preclinical investigations and selected clinical observational studies support an association between higher vitamin D intake and 25-hydroxyvitamin D levels with lower breast cancer risk. However, the recently updated report from the Institute of Medicine concluded that, for cancer and vitamin D, the evidence was 'inconsistent and insufficient to inform nutritional requirements'. Against this background, reports examining vitamin D intake, 25-hydroxyvitamin D levels and breast cancer incidence and outcome were reviewed. Current evidence supports the pursuit of several research questions but not routine 25-hydroxyvitamin D monitoring and vitamin D supplementation to reduce breast cancer incidence or improve breast cancer outcome.

Figure 1

Vitamin D and total mortality in a meta-analysis of randomized controlled trials. Meta-analysis of randomized, controlled trials evaluating supplementation with vitamin D alone or in combination with calcium compared with placebo or no intervention on total mortality. The size of the box indicates the number of deaths, and the horizontal lines indicate the 95% confidence interval (CI). Adapted with permission from Autier and Gandini [73]. RR, relative risk.

Figure 2

Total vitamin D intake and serum 25-hydroxyvitamin D by quintile. Individual total vitamin D intake (diet plus supplementation) and serum 25-hydroxyvitamin D (25(OH)D) levels at baseline. Serum 25(OH)D levels from 1,067 women identified as control subjects from a nested case-control study performed in the Women's Health Initiative trial evaluating calcium and vitamin D. Daily intakes of dietary and supplemental vitamin D were determined from self-report. The range of vitamin D intakes substantially overlaps in each 25(OH)D quintile. Line segments connect the mean vitamin D intake level in each quintile, which was 23.6, 38.5, 49.2, 60.9, and 81.9 nmol/l, respectively. Adapted with permission from Chlebowski and colleagues [42].