Formation of nitrosamines during consumption of nitrate- and amine-rich foods, and the influence of the use of mouthwashes.

We studied the formation of carcinogenic nitrosamines during consumption of food rich in nitrate and amines, and its possible inhibition by use of an antibacterial mouthwash. Twelve volunteers were fed a diet containing the high-nitrate vegetables lettuce or spinach during two periods of four consecutive days, in combination with fish products containing high levels of amines as nitrosatable precursors. During the two periods, the subjects used an antibacterial mouthwash containing chlorhexidine or a control mouthwash without antibacterial activity. Twenty-four-hour urine samples were collected after consumption of the meals, and saliva samples were collected 1 h after each meal. The nitrate and nitrite contents of the urine and saliva samples were determined by spectrophotometry (for nitrite) and HPLC (for nitrate). The concentrations of volatile nitrosamines in the urine samples were determined by gas chromatography-mass spectrometry. Significant increases in mean urinary nitrate levels (from 59 to 135 mg/24 h) and in mean salivary nitrate levels (from 10 to 56 microg/ml) and salivary nitrite levels (from 2 to 11 microg/ml) were observed during the consumption of food rich in nitrate and amines, as well as a significant increase in the mean urinary excretion of total examined volatile nitrosamines (from 2 to 7 nmol/24 h) and of N-nitrosodimethylamine (from 1.2 to 2.9 nmol/24 h). Use of the antibacterial mouthwash resulted in a decrease in mean salivary nitrite levels from 16 to 3 microg/ml and a decrease in mean urinary excretion of N-nitrosomorpholine (from 7.0 to 0.3 nmol/24 h). For the whole data set, significant correlations were observed between nitrate intake in food and urinary nitrate (p = 0.01; r2 = 0.07) and between urinary nitrate and urinary N-nitrosodimethylamine (p = 0.002; r2 = 0.11). In conclusion, consumption of a diet rich in nitrate and amines increases the risk of formation of carcinogenic nitrosamines. Use of an antibacterial mouthwash containing chlorhexidine can result in inhibition of nitrosamine formation.