Association between exposure to second-hand smoke and telomere length: cross-sectional study of 1303 non-smokers

Both active smoking and second-hand smoke (SHS) are important risk factors for many age-related diseases. Active smoking is associated with shortened telomere length. However, whether SHS accelerates telomere attrition with age is uncertain. The aim of this study was to examine the association between SHS exposure and shortening by age of leukocyte telomere length among adult non-smokers. We undertook a cross-sectional study of the association between self-reported levels of SHS exposure and telomere length shortening per annum on a subgroup of participants from the Scottish Family Health Study. Inclusion was restricted to non-smokers aged >= 18 years, who had provided self-reported overall usual SHS exposure (total hours per week) and blood samples for telomere analysis. Linear regression models were used to compare the ratio of telomere repeat copy number to single copy gene number (T/S)by age according to SHS exposure. Of the 1303 eligible participants, 779 (59.8%) reported no SHS exposure, 495 (38.0%) low exposure (1-19 h per week) and 29 (2.2%) high exposure (>= 20 h per week). In the univariate linear regression analyses, relative T/S ratio declined with increasing age in all exposure groups. Telomere length decreased more rapidly with increasing age among those with high exposure to SHS [adjusted coefficient -0.019, 95% confidence interval (CI) -0.031- -0.007) when compared with both those with no exposure to SHS (adjusted coefficient -0.006, 95% CI -0.008- -0.004) (high vs no SHS: P = 0.010) and those with low exposure to SHS (adjusted coefficient -0.005, 95% CI -0.007- -0.003) (high vs low SHS: P = 0.005). Our findings suggest that high SHS exposure may accelerate normal biological ageing, and support efforts to protect the public from SHS exposure. Further studies on relevant mechanisms should be conducted.