Dietary nicotine: a source of urinary cotinine.

Foods, principally from plants in the family Solanaceae, and a number of teas were examined for the presence of nicotine. Dietary nicotine would give rise to cotinine in urine and compromise estimates of exposure to tobacco smoke that depend on urinary cotinine. All foods were homogenized, extracted and analysed for nicotine and cotinine by gas chromatography with nitrogen-sensitive detection (GC) and/or GC/MS (mass spectrometry). Weak acid and aqueous extracts of the teas were analysed in a similar manner. Nicotine was not detected (less than 1 ng/ml of extract) in egg plant or green pepper. The average values for nicotine in tomato and potato were 7.3 ng/g wet weight and 15 ng/g wet weight, respectively. Black teas, including regular and decaffeinated brands, had nicotine contents ranging from non-detectable to greater than 100 ng/g wet weight. Instant teas yielded the highest nicotine contents observed (up to 285 ng/g wet weight). The possible sources of nicotine in these foods are discussed. A range of potential values for urinary cotinine concentrations (0.6 to 6.2 ng/ml) was calculated based upon estimated average and maximal consumptions of these foods and beverages. Because of the potential for exposure to nicotine by way of these routes, the use of urinary cotinine as a biomarker of exposure to environmental tobacco smoke may be compromised.