Nitrate and nitrite concentrations in human saliva for men and women at different ages and times of the day and their consistency over time

Salivary nitrite arises from nitrate and is the main source of gastric nitr ite, a precursor of carcinogenic N-nitroso compounds. We examined nitrate a nd nitrite levels in unstimulated saliva from subjects consuming low-nitrat e low-vitamin C diets. When saliva was collected from six men at nine times of the day (Experiment 1), night time nitrite levels were significantly hi gher than day time values and nitrite varied more than nitrate, When saliva was collected from 29 subjects aged 19-37 or 60-84 years at four times of the day during 1991-1993 (Experiment 2), all older subjects and older men h ad significantly higher nitrite levels than the corresponding younger subje cts, night time nitrite levels in men were significantly raised, and nitrat e and nitrite levels in the same samples were closely correlated. Saliva wa s collected at 6.00 a.m. on two successive days in 1997 from 16 subjects wh o had collected saliva in 1991-1993 (Experiment 3). Nitrate and nitrite lev els on day 1 of experiment 3 were closely correlated with those on day 2. N itrate and nitrite levels on days 1 and 2 of Experiment 3 were correlated w ith the corresponding parameters in Experiment 2 with P = 0.04 and 0.08 for day 1, and 0.10 and 0.28 for day 2, respectively. Hence, saliva nitrite le vels rose at night and were higher in older people, especially older men, a nd saliva nitrate and nitrite levels varied little from day to day, but var ied more after 4-6 years. (C) 2000 Lippincott Williams & Wilkins.