1.
Effects of inorganic nitrate and nitrite consumption on cognitive function and cerebral blood flow: A systematic review and meta-analysis of randomized clinical trials.
Clifford, T, Babateen, A, Shannon, OM, Capper, T, Ashor, A, Stephan, B, Robinson, L, O'Hara, JP, Mathers, JC, Stevenson, E, et al
Critical reviews in food science and nutrition. 2019;(15):2400-2410
Abstract
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.
2.
Association between dietary nitrate and nitrite intake and sitespecific cancer risk: evidence from observational studies.
Xie, L, Mo, M, Jia, HX, Liang, F, Yuan, J, Zhu, J
Oncotarget. 2016;(35):56915-56932
Abstract
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.
3.
Oxidative stress and antioxidant parameters in patients with major depressive disorder compared to healthy controls before and after antidepressant treatment: results from a meta-analysis.
Jiménez-Fernández, S, Gurpegui, M, Díaz-Atienza, F, Pérez-Costillas, L, Gerstenberg, M, Correll, CU
The Journal of clinical psychiatry. 2015;(12):1658-67
Abstract
OBJECTIVE To investigate the role of oxidative stress and antioxidants in depression. DATA SOURCES We searched the literature without language restrictions through MEDLINE/PubMed, Cochrane Library, Fisterra, and Galenicom from database inception until December 31, 2013, supplemented by a hand search of relevant articles. Search terms included (1) oxidative stress, antioxidant*, nitrosative stress, nitrative stress, nitro-oxidative stress, free radical*, and names of individual oxidative stress markers/antioxidants and (2) depression and related disorders and antidepressant. STUDY SELECTION Included were studies in patients with depression comparing antioxidant or oxidative stress markers with those in healthy controls before and after antidepressant treatment. DATA EXTRACTION Two authors independently extracted the data for antioxidant or oxidative stress markers. Standardized mean differences (SMDs) ± 95% confidence intervals (CIs) for results from ≥ 3 studies were calculated. DATA SYNTHESIS Altogether, 29 studies (N = 3,961; patients with depression = 2,477, healthy controls = 1,484) reported on the oxidative stress marker malondialdehyde (MDA) and total nitrites, the antioxidants uric acid and zinc, or the antioxidant-enhancing enzymes superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPX). When patients with depression were compared with healthy controls, depression was associated with higher oxidative stress MDA levels (8 studies; n = 916; SMD = 1.34; 95% CI, 0.57 to 2.11; P < .001), lower antioxidant uric acid (4 studies; n = 512; SMD = -0.64; 95% CI, -1.22 to -0.06; P = .030) and zinc levels (13 studies; n = 2,002; SMD = -0.66; 95% CI, -0.98 to -0.34; P < .0001), and higher antioxidant-enhancing enzyme SOD levels (11 studies; n = 902; SMD = 0.62; 95% CI, 0.07 to 1.17; P = .028), while differences in total nitrites and CAT and GPX were nonsignificant. Antidepressant treatment, which significantly reduced Hamilton Depression Rating Scale scores (24.6 ± 0.7 to 16.2 ± 1.6; SMD = 2.65; 95% CI, 1.13 to 4.15; P = .00065), reduced MDA (4 studies; n = 194; SMD = -1.45; 95% CI, -2.43 to -0.47; P = .004) and increased uric acid (3 studies; n = 212; SMD = 0.76; 95% CI, 0.03 to 1.49; P = .040) and zinc levels (3 studies; n = 65; SMD = 1.22; 95% CI, 0.40 to 2.04, P = .004), without differences in MDA (P = .60), uric acid (P = .10), and zinc (P = .163) levels compared to healthy controls. CONCLUSIONS Results suggest that oxidative stress plays a role in depression and that antidepressant activity may be mediated via improving oxidative stress/antioxidant function.