title: Examining the association of circulating 25-hydroxyvitamin D with kidney cancer risk: a meta-analysis.
abstract: OBJECTIVE
  To examine the relationship between circulating 25-hydroxy-vitamin D (25 (OH) D) and risk of kidney cancer.
  
  
  METHODS
  We searched PubMed, EMBASE, and Web of Science databases through August 31, 2015 for eligible studies. Pooled ORs with 95% confidence interval were calculated using fixed effect models. All data analyses were performed with STATA version 12.0.
  
  
  RESULTS
  The final analysis included 2 prospective cohort studies and 7 nested case-control studies, with a total of 130, 609 participants and 1, 815 cases of kidney cancer. No obvious heterogeneity was observed between individual studies. The results of this study revealed that higher circulating 25-hydroxyvitamin D levels were associated with lower risk of kidney cancer (OR=0.79, 95% CI 0.69-0.91; P value for heterogeneity: 0.61, I(2)=0%). After stratified by geographical region, the similar association was detected in European studies (OR=0.81, 95% CI 0.69-0.94; P value for heterogeneity: 0.38, I(2)=0%), though no significant association was observed in the USA studies (OR=0.73, 95% CI 0.51-1.04; P value for heterogeneity: 0.44, I(2)=0%).
  
  
  CONCLUSIONS
  Our present findings suggest that higher levels of circulating 25-hydroxyvitamin D could reduce the risk of kidney cancer by 21%. Further well-designed large-scaled prospective studies and randomized controlled trials are warranted to provide more conclusive evidence.
authors.affiliation: Department of Urology, Nanfang Hospital, Southern Medical University Guangzhou 510515, Guangdong, P. R. China.
authors.forename: Guangzheng
authors.initials: G
authors.lastname: Lin
authors.affiliation: Department of Infectious Diseases and Hepatology Unit, Nanfang Hospital, Southern Medical University Guangzhou 510515, Guangdong, P. R. China.
authors.forename: Ling
authors.initials: L
authors.lastname: Ning
authors.affiliation: Department of Urology, Nanfang Hospital, Southern Medical University Guangzhou 510515, Guangdong, P. R. China.
authors.forename: Di
authors.initials: D
authors.lastname: Gu
authors.affiliation: Department of Urology, Nanfang Hospital, Southern Medical University Guangzhou 510515, Guangdong, P. R. China.
authors.forename: Shi
authors.initials: S
authors.lastname: Li
authors.affiliation: Department of Urology, Nanfang Hospital, Southern Medical University Guangzhou 510515, Guangdong, P. R. China.
authors.forename: Zhe
authors.initials: Z
authors.lastname: Yu
authors.affiliation: Department of Urology, Nanfang Hospital, Southern Medical University Guangzhou 510515, Guangdong, P. R. China.
authors.forename: Qicheng
authors.initials: Q
authors.lastname: Long
authors.affiliation: Department of Health Management, Nanfang Hospital, Southern Medical University Guangzhou 510515, Guangdong, P. R. China.
authors.forename: Li-Na
authors.initials: LN
authors.lastname: Hou
authors.affiliation: Department of Urology, Nanfang Hospital, Southern Medical University Guangzhou 510515, Guangdong, P. R. China.
authors.forename: Wan-Long
authors.initials: WL
authors.lastname: Tan
keywords: 25-hydroxyvitamin D; Kidney cancer; meta-analysis; renal cell carcinoma; risk