Impact of oral vitamin D supplementation on serum 25-hydroxyvitamin D levels in oncology

BACKGROUND: Serum 25-hydroxyvitamin D [25(OH)D] is the major circulating form of vitamin D and a standard indicator of vitamin D status. Emerging evidence in the literature suggests a high prevalence of suboptimal vitamin D (as defined by serum 25(OH)D levels of <32 ng/ml) as well as an association between lower serum levels and higher mortality in cancer. We investigated the effect of oral vitamin D supplementation as a means for restoring suboptimal levels to optimal levels in cancer. METHODS: This is a retrospective observational study of 2198 cancer patients who had a baseline test prior to initiation of cancer therapy at our hospital to evaluate serum 25(OH)D levels between Jan 08 and Dec 09 as part of their initial nutritional evaluation. Patients with baseline levels of < = 32 ng/ml (n = 1651) were considered to have suboptimal serum 25(OH)D levels and were supplemented with 8000 IU of Vitamin D3 (four 2000 IU D3 capsules) daily as part of their nutritional care plan. The patients were retested at their first follow-up visit. Of 1651 patients, 799 were available for follow up assessment. The mean serum 25(OH)D levels were compared in these 799 patients across the 2 time points (baseline and first follow-up) using paired sample t-test. We also investigated the factors associated with response to vitamin D supplementation. RESULTS: Of 2198 patients, 814 were males and 1384 females. 1051 were newly diagnosed and treated at our hospital while 1147 were diagnosed and treated elsewhere. The mean age at presentation was 55.4 years. The most common cancer types were breast (500, 22.7%), lung (328, 14.9%), pancreas (214, 9.7%), colorectal (204, 9.3%) and prostate (185, 8.4%). The mean time duration between baseline and first follow-up assessment was 14.7 weeks (median 10.9 weeks and range 4 weeks to 97.1 weeks). The mean serum 25(OH)D levels were 19.1 ng/ml (SD = 7.5) and 36.2 ng/ml (SD = 17.1) at baseline and first follow-up respectively; p < 0.001. Patients with prostate and lung cancer had the highest percentage of responders (70% and 69.2% respectively) while those with colorectal and pancreas had the lowest (46.7% each). Similarly, patients with serum levels 20-32 ng/ml at baseline were most likely to attain levels > 32 ng/ml compared to patients with baseline levels < 20 ng/ml. CONCLUSIONS: The response to supplementation from suboptimal to optimal levels was greatest in patients with prostate and lung cancer as well as those with baseline levels between 20-32 ng/ml. Characteristics of non-responders as well as those who take longer to respond to supplementation need to be further studied and defined. Additionally, the impact of improved serum 25(OH)D levels on patient survival and quality of life needs to be investigated.