A clinical study examining the effects of dietary nitrate on urinary N-nitrosamines

BACKGROUND Inorganic nitrate from dietary sources has raised health concerns due to its possible conversion into carcinogenic N-nitrosamines, leading to strict regulations on nitrate levels in food and drinking water.

OBJECTIVE In this study, which was a part of a larger randomized controlled trial, we evaluated urinary excretion of N-nitrosamines in response to daily dietary nitrate intake over a 5-week period, using two different forms of nitrate administration.

METHODS A total of 231 participants with mild hypertension were randomized into three groups. Group 1 (n=78) consumed vegetables low in nitrate along with a placebo capsule (300 mg potassium chloride, KCl). Group 2 (n=77) received the same low-nitrate vegetables plus a potassium nitrate supplement (300 mg KNO3). Group 3 (n=77) consumed nitrate-rich leafy green vegetables providing 300 mg nitrate daily plus the placebo capsule. Twenty-four-hour urine samples were collected before and after the intervention. Nitrate was measured with High-Pressure Liquid Chromatography (HPLC) and N-nitrosamine levels were quantified using Ultra High-Pressure Liquid Chromatography-tandem Mass spectrometry (UHPLC-MS/MS). A paired t-test was used for statistical analyses.

RESULTS As expected, urinary nitrate increased approximately five-to sixfold in participants receiving nitrate-rich vegetables or potassium nitrate compared to those receiving potassium chloride. Total urinary excretion of N-nitrosamines was low across all groups under basal conditions (below 5 ug/24h) and did not significantly change following the intervention. A similar lack of change was observed for each of the 7 individual N-nitrosamine species measured.

CONCLUSION These findings suggest that a 5-week dietary intake of nitrate mostly exceeding the current consensus for upper limit of the acceptable daily intake (3.7 mg/kg/day), whether provided as a vegetable source or as a nitrate salt, does not increase urinary excretion of N-nitrosamines.

CLINICAL TRIAL REGISTRY NUMBER NCT02916615 clinicaltrials.gov.