A meta-analysis of 18 existing datasets suggests that leukocyte telomere shortening is not accelerated by smoking. The data imply that adult leukocyte telomere length (LTL) should be viewed as a biomarker that changes relatively little in adult life as a result of smoking.
The 18 longitudinal studies were collated from 10 countries, over 4 continents. The combined dataset is the largest of its kind, incorporating data on 12,579 individuals, aged between 26 and 80 years. 4678 of the individuals are current smokers and 7901 are non-smokers.
Only studies in which LTLs of patients were obtained at baseline and follow-up were included in this meta-analysis. To ensure sufficient time for meaningful biological changes to have taken place, a minimum follow-up period of 4 years was another prerequisite to study inclusion in the meta-analysis.
The data corroborates that smokers have detectably lower LTLs than non-smoking individuals. However, there was no evidence of substantially accelerated telomere shortening in smokers over non-smokers. This suggests that smoking is likely not directly causing the greater shortening of telomeres observed in smokers. Melissa Bateson, lead study researcher from Newcastle University’s Faculty of Medical Sciences (Newcastle, UK), commented that the study does not “dispute the abundant evidence that smoking is bad for you, but merely the evidence that telomere length is a good way of assessing the biological damage done by smoking”.
Bateson continued: “For the scientific community it means that measuring changes in adult telomere length may be less useful than previously thought for identifying behavior that is harmful and for monitoring the consequences of behavior change.”
The root question of what then does cause smokers to have shorter LTLs remains unanswered. The team of international researchers that collaborated to share the 18 datasets analyzed in this study suggest the answer may lie in an unidentified third variable that links smoking and shorter LTL. Newcastle University is continuing research into this.
Bateson concluded that: “…the findings underline the need for caution when interpreting correlational data. Just because two variables are correlated does not mean that one variable causes the other.”
The findings may also impact on how telomere length measures are used in epidemiology. If, as the data suggest, telomere lengths are static biomarkers, they may no longer be able to be used to identify behaviors that accelerate telomere shortening.
Bateson M, Aviv A, Bendix L et al. Smoking does not accelerate leucocyte telomere attrition: a meta-analysis of 18 longitudinal cohorts. R. Soc. Open Sci. 6: 190420 (2019);