Serum vitamin D decreases during chemotherapy: an Australian prospective cohort study

Background and Objectives: Vitamin D plays an important role in bone and muscle function, and cell proliferation. The impact of chemotherapy and associated behavioural changes such as fatigue and sun avoidance on vitamin D (25(OH) D) is unknown. This study aims to evaluate variations in serum vitamin D during chemotherapy and the predictive value of latitude, season and pre-existing vitamin D deficiency. Methods and Study Design: A 12-week prospective cohort study was conducted in chemotherapy-naive patients in two Australian locations with different sun exposure. Vitamin D deficiency was defined as <= 25 nmol/L and insufficiency 26-50 nmol/L 25(OH) D. Demographics, chemotherapy regimen, nutritional status, sun exposure, geographic location, and season were collected at baseline, 6 and 12 weeks after commencing chemotherapy. Results: Eighty-five patients (mu 55.3 +/- 13.4 years of age; 49% female) were recruited, 96% Caucasian. Fifty-four patients were treated with curative intent (mostly for breast [n=29] or colorectal [n=12] cancers). At baseline, 10 patients were vitamin D deficient and 33 were insufficient. Mean serum 25(OH) D (nmol/L) was higher at latitude -27.5 degrees (Brisbane) than latitude -34.9 degrees (Adelaide) (mu 61.9 +/- 22.1 vs mu 42.2 +/- 19.2, p<0.001) and varied according to season (spring: mu 46.9 +/- 20.3, summer: mu 50.8 +/- 18.2, autumn: mu 76.4 +/- 25.2, winter: mu 36.5 +/- 15.7, p<0.001). Serum 25(OH) D decreased with chemotherapy (baseline: mu 49.2 +/- 22.3, 6-weeks: mu 40.9 +/- 19.0, 12-weeks: mu 45.9 +/- 19.7, p=0.05), with a significant and more rapid decline in winter and autumn (p=0.03). Conclusions: Chemotherapy is associated with a decrease in serum vitamin D, particularly during winter and autumn. Investigations into the underlying mechanism and associated potential outcomes with this decrease requires further investigation.