Smoking is associated with an age-related decline in exhaled nitric oxide.

Age-related declines in forced expiratory volume in one second are accelerated in smokers. Smoking is associated with decreased exhaled nitric oxide fraction (F(eNO)). The aim of the present study was to determine the impact of age on F(eNO) in otherwise healthy smokers and nonsmokers. F(eNO) and serum cotinine levels were measured in 994 healthy subjects aged 18-40 yrs. American Thoracic Society questionnaire data on smoking habits was used to validate serum cotinine levels as a surrogate marker for categorisation of smokers and nonsmokers in the cohort. Serum cotinine levels were a good discriminator of smokers (n = 99) and nonsmokers (n = 895). F(eNO) levels were significantly lower in otherwise healthy smokers compared with nonsmokers. There was an inverse correlation of serum cotinine levels with F(eNO). No correlation of age with F(eNO) was found in nonsmokers but an inverse correlation of F(eNO) with age in smokers was found. F(eNO) was significantly lower in smokers aged 21-40 yrs compared with nonsmokers aged 21-40 yrs, but was not lower in smokers aged 18-20 yrs compared with nonsmokers of the same age. Smoking was associated with decreased exhaled nitric oxide. The greatest smoking-related declines in exhaled nitric oxide occurred in older subjects. This suggests that smoking is associated with age-related declines in exhaled nitric oxide and justifies future mechanistic studies that address the impact of exhaled nitric oxide decline on lung function.