Figure 2. General third variable model of pack-years of smoking, BMI and LTL. β, c and c’ are standardized regression coefficients; c=total effect; c’=direct effect; β1=indirect effect 1; β2=indirect effect 2; βInd=total indirect effect; BMI=body mass index; LTL=leukocyte telomere length. * P<0.05; ** P<0.01.