Vitamin D levels in Swiss breast cancer survivors

Cholecalciferol (vitamin D3) is widely supplemented in breast cancer survivors because of the role of vitamin D in multiple health outcomes. We conducted an observational study in 332 women in Eastern Switzerland with early, i.e., nonmetastatic breast cancer. Tumour-, patient-related and sociodemographic variables were recorded. Cholecalciferol intake and serum 25-hydroxyvitamin D (25(OH)D) and 1,25-dihydroxyvitamin D (1,25(OH)2D) levels were measured at the first visit (baseline) and during a follow-up visit in a median of 210 days (range 87-857) after the first visit. Patients presenting 25(OH)D deficiency were advised to take cholecalciferol supplementation. At baseline, 60 (18%) patients had 25(OH)D deficiency (≤50 nmol/l, ≤20 ng/l), and 70 (21%) had insufficiency (50-74 nmol/l, 20-29 ng/l). Out of 121 patients with ongoing cholecalciferol supplementation at baseline, 25(OH)D deficiency and insufficiency was observed in 9 (7%) and 16 (13%) patients, respectively, whereas out of 52 patients with no supplementation, 15 (29%) had deficiency and 19 (37%) had insufficiency. Only 85 (26%) patients had optimal 25(OH)D levels (75-100 nmol/l, 30-40 ng/l) at baseline. Seasonal variation was significant for 25(OH)D (p = 0.042) and 1,25(OH)2D (p = 0.001) levels. Living in a rural area was associated with a higher median 25(OH)D concentration as compared with living in an urban area (87 nmol/l, range 16-216 vs 72 nmol/l, range 17-162; p = 0.001). Regular sporting activity was positively associated with 25(OH)D (p = 0.045). Body mass index was inversely related to both 25(OH)D and 1,25(OH)2D (Spearman's rho = -0.24, p