A worldwide systematic review, meta-analysis and meta-regression of nitrate and nitrite in vegetables and fruits

This study aimed to conduct on the concentration of nitrate/nitrite (mg kg-1) in vegetables and fruits with a special emphasize on the effect of climate condition. The highest concentration (mean and 95%CI) of nitrate/nitrite was determined in Rocket (4825.15; 3044.14–6606.16), Mizuna (3500; 2702.48–4297.52), and Bok choy (3407.40; 2841.39–3973.42) in vegetable group and in wolfberry (2395.83; 1611.89–3179.77), Jack fruit (237.8; 202.88–272.71) and Cantaloupe (220.32; −224.53 to 665.19) in fruits group. Brazil (2816.77), Estonia (2133.76), Republic of China, Taiwan (2118.28) were the nations with the highest average concentration of nitrate/nitrite in all samples taken from these nations across the globe. Furthermore, Chinese fruits contain the highest concentrations of nitrates/nitrites of other countries (500.57; 416.74–584.41). Nitrate is present in greater quantities in fruits (44.02; 42.12–45.93) and vegetables (438.31; 422.51–454.11) than nitrite; however, the quantity of nitrite has a relatively similar content in both. Our findings revealed that increase in humidity (> 60%), annual rainfall (> 1500 mm), average temperature (> 10 °C) and application of fertilizers lead to significant increase in accumulation of nitrate/nitrite composition of vegetables and fruits (p < 0.05). According to the results of rating countries using the Food Security Index (GFSI), countries with high scores—like Poland and Portugal, which have GFSI scores of 75.5 and 78.7 and average contamination levels of 8.26 and 11.08, respectively—have a trend of average nitrate/nitrite levels of fruit and vegetable products that is significantly decreasing (p = 0.00). Although GFSI levels and other environmental variables can influence nitrate/nitrite levels, fertilizer usage (kg ha-1) is one of the most significant controllable and impactful factors in contaminants residue, which should be manage. The result of our study, will serve as a basis to estimate the dietary exposure to nitrates and nitrites from fruits and vegetables among populations around the world based on climatology and monitor the related health outcomes.