Association between dietary nitrate and nitrite intake and site-specific cancer risk: evidence from observational studies
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Li Xie1,3,*, Miao Mo1,3,*, Hui-Xun Jia1,3, Fei Liang1,3, Jing Yuan1,3, Ji Zhu1,2,3
1Clinical Statistics Center, Fudan University Shanghai Cancer Center, Shanghai, China
2Department of Radiation Oncology, Fudan University Shanghai Cancer Center, China
3Department of Oncology, Shanghai Medical College, Fudan University, Shanghai, China
*These authors have contributed equally to this work
Ji Zhu, email: email@example.com
Keywords: nitrate, nitrite, cancer, risk, meta-analysis
Received: January 06, 2016 Accepted: July 18, 2016 Published: July 29, 2016
Epidemiological studies have reported inconsistent findings on the association between dietary nitrate and nitrite intake and cancer risk. We performed a meta-analysis of epidemiological studies to summarize available evidence on the association between dietary nitrate and nitrite intake and cancer risk from published prospective and case-control studies. PubMed database was searched to identify eligible publications through April 30th, 2016. Study-specific relative risks (RRs) with corresponding 95% confidence interval (CI) from individual studies were pooled by using random- or fixed- model, and heterogeneity and publication bias analyses were conducted.
Data from 62 observational studies, 49 studies for nitrates and 51 studies for nitrites, including a total of 60,627 cancer cases were analyzed. Comparing the highest vs. lowest levels, dietary nitrate intake was inversely associated with gastric cancer risk (RR = 0.78; 95%CI = 0.67-0.91) with moderate heterogeneity (I2 = 42.3%). In contrast, dietary nitrite intake was positively associated with adult glioma and thyroid cancer risk with pooled RR of 1.21 (95%CI = 1.03-1.42) and 1.52 (95%CI = 1.12-2.05), respectively. No significant associations were found between dietary nitrate/nitrite and cancers of the breast, bladder, colorectal, esophagus, renal cell, non-Hodgkin lymphoma, ovarian, and pancreas. The present meta-analysis provided modest evidence that positive associations of dietary nitrate and negative associations of dietary nitrite with certain cancers.
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