Nitrate and nitrite concentrations in human saliva: variations with salivary flow-rate

Salivary nitrate concentration has often been used as a measure of human intake of nitrate. However, our findings indicate that this is not a reliable indicator because the nitrate concentration varies with salivary flow-rate and thus depends on the sampling procedure. Parotid or whole saliva was collected from up to six volunteers under carefully controlled conditions. The effects of stimulating saliva production by chewing on silicon tube (mechanical stimulation) or by sucking citric acid from cotton wool (gustatory stimulation) were investigated. Chewing decreased the average nitrate (plus nitrite) concentration in whole saliva by 59% and the nitrate concentration in parotid saliva (which does not contain nitrite) by 53%, relative to unstimulated saliva. Citric acid stimulation decreased the average parotid salivary nitrate concentration by 88%. Stimulation of salivary secretion increased the total salivary nitrate output and the extent of reduction of nitrate to nitrite for most subjects. The unstimulated parotid salivary nitrate concentration was, on average, 2.8 times the nitrate plus nitrite concentration in unstimulated whole saliva.