Objectives: The optimal concentration of individual vitamin D intake for preventing bladder cancer has not, to our knowledge, been defined. To evaluate the comparative efficacy of different serum 25-hydroxyvitamin D concentrations in preventing bladder cancer, we conducted a systematic search of the literature published up to April 2015.
Methods: We applied a pairwise meta-analysis to estimate direct evidence from intervention-control studies and a network meta-analysis within a Bayesian framework to combine direct and indirect evidence. Moreover, a dose-response curve was utilized to predict the optimal median serum 25-hydroxyvitamin D concentration based on the odds ratio (OR) for each quintile concentration.
Methods: Seven studies of a total of 90757 participants, including 2509 bladder cancer patients, were included. Two prospective cohort studies with 57 591 participants and 494 bladder cancer patients, and five case-control studies with 33 166 participants and 2264 bladder cancer patients. From the network meta-analysis, we observed that sufficient serum 25-hydroxyvitamin D concentrations (>75 nmol/L) were superior to all other 25-hydroxyvitamin D concentrations in decreasing the risk of bladder cancer: OR = 0.68 and 95% credible interval (CrI) 0.52 to 0.87 compared with severely deficient concentrations (<25 nmol/L); OR = 0.65 and 95% CrI 0.49 to 0.86 compared with moderately deficient concentrations (25-37.5 nmol/L); OR = 0.61 and 95% CrI 0.47 to 0.80 compared with slightly deficient concentrations (37.5-50 nmol/L); and OR = 0.65 and 95% CrI 0.48 to 0.85 compared with insufficient concentrations (50-75 nmol/L). In addition, we noted a roughly inverse correlation between bladder cancer risk and 25-hydroxyvitamin D concentrations (R(2) = 0.98, P = 0.007).
Conclusions: Ensuring sufficient serum 25-hydroxyvitamin D concentrations might play an important role in decreasing the risk of bladder cancer. The serum 25-hydroxyvitamin D concentration ≥74 nmol/L was associated with a 60% lower risk of bladder cancer incidence.
Keywords: Bladder cancer; Network meta-analysis; Serum 25-hydroxyvitamin D; Systematic review; Vitamin D.
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