***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: Inconsistent associations between smoking and telomere length ( TL ) have been reported in epidemiologic studies , perhaps because of the time-varying nature of smoking behaviors . We estimated the associations of TL , which was measured by quantitative polymerase chain reaction using saliva DNA , with concurrent and past smoking status reported biennially for up to 16 years before TL measurement in 5,624 participants in the Health and Retirement Study ( 1992 - 2008 ) . Smoking was associated with reduced TL when we used prospect i ve data on smoking statuses among men and women , but the association was strongly attenuated among men in cross-sectional analyses . This attenuation was largely due to a higher rate of smoking cessation during the study period among men with shorter TL than among men with longer TL . Short TL was also associated with poorer overall health in men , which suggests that male smokers with short TL were more likely to quit smoking because of poor health . Analyses of years since cessation , smoking duration , and pack-years of smoking all support the hypothesis that increased cigarette use shortens TL . Our results provide a potential explanation for the inconsistent associations between smoking and TL reported in previous cross-sectional studies . Time-varying associations should be considered in future studies of smoking behavior , TL , aging , and disease risk Background : Within-person variability in biomarkers results in r and om error that can attenuate estimates of association . Little information on such variability is available for a number of nutrition-related biomarkers . Methods : Blood sample s obtained 2 to 4 weeks apart were analyzed for tocopherols , carotenoids , ascorbate , lipids , cotinine , C-reactive protein , and oxidative stress . Subjects ( n = 206 men and women , mean age 45.4 years ) were either smokers or passively exposed to smoke . We calculated intraindividual and interindividual variability and the number of measurements required to reduce attenuation . Results : For most biomarkers , 2 measurements would be required to limit the attenuation of correlation coefficients to no lower than 90 % of the true correlation . If only one measurement were obtained , observed correlations would be approximately 80–88 % of true correlations . For regression coefficients , 3 or 4 measures would be required . Exceptions were ascorbic acid and malondialdehyde , for which a single measure result ed in little attenuation . Conclusions : For most serum markers , collection of 2 or more measurements per person is desirable to increase the ability to detect associations between biomarkers and health-related variables . If only one measure is possible , sample sizes should be planned to permit detection of associations that are likely to be observed , not the theoretical true associations . The results of this study , in which measurements were obtained 2 to 4 weeks apart , are relevant for epidemiologic research in which the exposure of interest is the subject ’s baseline or current status . It is likely that within-person variability would be greater over a period of months or years 
    Output:
    
Similarly , shorter telomere length was found among smokers compared to non‐smokers , and among current smokers compared to never or former smokers .
Dose‐response meta‐ analysis suggested an inverse trend between pack‐years of smoking and telomere length .
Conclusion Shorter telomeres among ever smokers compared to those who never smoked may imply mechanisms linking tobacco smoke exposure to ageing‐related disease .
Telomere length was shorter in ever smokers compared to never smokers .
Among ever smokers , current smokers had shorter mean telomeres than former smokers .
An inverse trend was indicated between pack‐years of smoking and telomere length