When using lifetime smoking index as exposure, the results showed a trend similar to that of the smoking initiation analysis (OR, 1.49; 95% CI, 1.31–1.70; P = 2.5 × 10 −9 ; I 2 = 37%) ( Figure 3 and Supporting Information, Figure S1 ).
With only 10 SNPs used as instruments and a small proportion of the phenotypic variance (0.2%) explained, the power was not sufficient to assess the causal association between age at initiation of regular smoking and HF, especially considering the consistent effect estimates with wider CI that are close to significance.