We conducted a systematic review and meta-analysis of randomized clinical trials examining the effect of inorganic nitrate or nitrite supplementation on cognitive function (CF) and cerebral blood flow (CBF). Two databases (PubMed, Embase) were searched for articles from inception until May 2017. Inclusion criteria were: randomized clinical trials; participants >18 years old; trials comparing a nitrate/nitrite intervention with a control. Thirteen and nine trials were included in the meta-analysis to assess CF and CBF, respectively. Random-effects models were used and the effect size described as standardized mean differences (SMDs). A total of 297 participants (median of 23 per trial) were included for CF; 163 participants (median of 16 per trial) were included for CBF. Nitrate/nitrite supplementation did not influence CF (SMD +0.06, 95% CI: -0.06, 0.18, P = 0.32) or CBF under resting (SMD +0.14, 95% CI: -0.13, 0.41, P = 0.31), or stimulated conditions (SMD + 0.23, 95% CI: -0.11, 0.56, P = 0.19). The meta-regression showed an inverse association between duration of the intervention and CBF (P = 0.02) but no influence of age, BMI or dose (P < 0.05). Nitrate and nitrite supplementation did not modify CBF or CF. Further trials employing larger samples sizes and interventions with longer duration are warranted.

中文翻译：

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食用无机硝酸盐和亚硝酸盐对认知功能和脑血流的影响：随机临床试验的系统评价和荟萃分析

我们进行了随机临床试验的系统评价和荟萃分析，研究了补充无机硝酸盐或亚硝酸盐对认知功能（CF）和脑血流量（CBF）的影响。从开始到2017年5月，在两个数据库（PubMed，Embase）中搜索文章。参与者> 18岁；将硝酸盐/亚硝酸盐干预与对照进行比较的试验。荟萃分析中分别包括13个和9个试验以评估CF和CBF。使用随机效应模型，效应大小描述为标准化均值差（SMD）。共有297名参与者参加了CF（每项试验的中位数为23名）；包括163名参与者（每个试验中位数为16名）参加CBF。补充硝酸盐/亚硝酸盐不会影响CF（SMD +0.06，95％CI：-0。06、0.18，P = 0.32）或静息状态下的SBF（SMD +0.14，95％CI：-0.13，0.41，P = 0.31）或刺激条件下（SMD + 0.23，95％CI：-0.11，0.56，P = 0.19）。荟萃回归显示干预持续时间与脑血流量呈负相关（P = 0.02），但不受年龄，BMI或剂量的影响（P <0.05）。补充硝酸盐和亚硝酸盐不会改变CBF或CF。有必要采用更大的样本量和更长的干预时间进行进一步的试验。