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

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

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-wk period using 2 different forms of nitrate administration.

A total of 231 participants with mild hypertension were randomly assigned into 3 groups. Group 1 (n = 78) consumed vegetables low in nitrate along with a placebo capsule (300 mg potassium chloride). Group 2 (n = 77) consumed the same low-nitrate vegetables plus a potassium nitrate supplement (300 mg). 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 and N-nitrosamine concentrations were quantified using ultra high-pressure liquid chromatography-tandem mass spectrometry. A paired t-test was used for statistical analyses.

As expected, urinary nitrate increased ∼5- to 6-fold in participants consuming nitrate-rich vegetables or potassium nitrate compared with those consuming potassium chloride. Total urinary excretion of N-nitrosamines was low across all groups under basal conditions (<5 μg/24 h) and did not significantly change after the intervention. A similar lack of change was observed for each of the 7 individual N-nitrosamine species measured.

These findings suggest that a 5-wk dietary intake of nitrate mostly exceeding the current consensus for upper limit of the acceptable daily intake (3.7 mg/kg/d), whether provided as a vegetable source or as a nitrate salt, does not increase urinary excretion of N-nitrosamines. This study was registered at clinicaltrials.gov as NCT02916615.