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

¹ Dept of Medicine, Division of Rheumatology and Immunology, ² Division of Pulmonary, Allergy and Critical Care Medicine, and ³ Dept of Paediatrics, Division of Allergy and Immunology, Duke University Medical Center, Durham, NC, USA.

CORRESPONDENCE: M. C. Levesque, Duke University Medical Center, Box 3266, Durham, NC 27710, USA. Fax: 1 9196844141. E-mail: marc.levesque{at}duke.edu

Keywords: Ageing, humans, nitric oxide, smoking

Received: July 12, 2007
Accepted September 17, 2007

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.