**Figure 1.** **General third variable model of smoking, BMI and LTL.** β, c and c’ are standardized regression coefficients; c=total effect; c’=direct effect; β_{1}=indirect effect 1; β_{2}=indirect effect 2; β_{Ind}=total indirect effect; BMI=body mass index; LTL=leukocyte telomere length. * P<0.05; ** P<0.01.