Carbonated drink consumption and increased exhaled nitric oxide in atopic children

  1. S. W. Turner 1 ,
  2. L. C. A. Craig 2 ,
  3. P. J. Harbour 1 ,
  4. S. H. Forbes 1 ,
  5. S. Martindale 2 ,
  6. G. McNeill 1 , 2 ,
  7. A. Seaton 2 ,
  8. J. G. Ayres 2 ,
  9. G. Devereux 2 and
  10. P. J. Helms 1
  1. Depts of 1Child Health, and 2Environmental and Occupational Medicine, University of Aberdeen, Aberdeen, UK.

To the Editors:

Fractional exhaled nitric oxide concentrations (FeNO) are elevated in asthmatic children and have been used inter alia to guide inhaled corticosteroid treatment in children 1. Caffeine consumption might influence FeNO independently of asthma and more than one plausible mechanism has been identified. Studies in adults have reported changes in FeNO within 1 h of caffeine ingestion but the results are inconsistent, with one study having reported reduced FeNO 2, one elevated FeNO 3 and another no change after ingestion 4.

An association between caffeine intake and altered FeNO is equally plausible in children but has not been sought. The predominant source of caffeine in children’s diet is carbonated drinks, in particular colas, and in Scotland “Irn Bru” (a carbonated orange-coloured drink). As part of a longitudinal birth cohort study where diet was related to asthma outcomes, including FeNO 5, we have been able to test the hypothesis that FeNO in 5-yr-old children is increased in association with regular intake of carbonated drinks.

Our methodology is described fully elsewhere 5. Briefly, parents were asked to complete a respiratory and food frequency questionnaire (FFQ) and they were invited to bring their child to the hospital for an assessment, including FeNO measurement and skin-prick reactivity to four common allergens. Atopy was defined as at least one positive skin-prick test. Drinks were described as either regular fizzy drinks (e.g. lemonade, Irn Bru, cola) or low-calorie fizzy drinks. Children’s intake of carbonated drinks at 5 yrs of age was ascertained by parents' responses to one of nine frequency-of-consumption categories ranging between “rarely or never” to “seven or more measures per day”. A measure was defined as half a standard can or one medium glass full, equivalent to 165 mL. For the purpose of the present study, carbonated drink consumption (“exposed” or “nonexposed”) was defined as at least one measure of carbonated drink per month. A standard chemiluminescence analyser (NIOX®; Aerocrine, Solna, Sweden) was used to measure FeNO at an expiratory flow of 50 mL·s−1.

Carbonated drinks (regular and/or diet) were consumed by 646 (58%) out of 1,111 children whose parents completed an FFQ. FeNO data were available in 157 children, of whom atopy was determined in 147. The median consumption of carbonated drinks was one per week (interquartile range one per month to two per week). There was a trend, which did not reach significance, for FeNO to be elevated among the 85 children who drank carbonated drinks (geometric mean±sem 6.8±0.7 ppb) compared with the remaining 72 children who did not (6.0±0.7 ppb; p = 0.112, Mann–Whitney U-test). We stratified by atopy, recognised as a confounder for FeNO. The FeNO values were 5.9±0.5, 5.4±0.5, 6.1±0.5 and 11.9±1.8 ppb in nonexposed nonatopic (n = 47), exposed nonatopic (n = 59), nonexposed atopic (n = 20) and exposed atopic (n = 21) children, respectively (fig. 1⇓). The latter was significantly higher (p<0.001) when compared with other groups. Multivariate analysis confirmed this association to be independent of asthma. We sought evidence of a dose–response relationship by dichotomising the 21 exposed atopic children: FeNO was 13.1±2.6 and 10.6±2.4 ppb among the higher and lower exposure groups, respectively.

Fig. 1—
Fig. 1—

A box-whiskers plot demonstrating median and interquartile ranges for fractional exhaled nitric oxide (FeNO, parts per billion (ppb)) across groups categorised by atopy and consumption of carbonated drinks. □: n = 47; ░: n = 20; ▒: n = 59; ▓: n = 21. ***: p<0.001 (ANOVA) for comparisons with other groups.

This exploratory study is the first to seek an association between caffeine intake and fractional exhaled nitric oxide in children. The clinical relevance of this association is not clear. Since approximately two-thirds of asthmatic children are atopic and many children consume caffeine-containing carbonated drinks, an association between fractional exhaled nitric oxide and caffeine in atopic children could be of clinical relevance and might also confound epidemiological studies. An intervention study is needed to study the relationship between fractional exhaled nitric oxide and caffeine intake in atopic children.

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