Use of cardioprotective medication, contact with health professionals, and medication prescription during the follow-up period in the cohort are given in Table 3. The multivariate-adjusted HRs for incident fatal and nonfatal IHD events in the treated vs untreated SCH individuals by age, in decades, are given in Table 4. Further analysis of the primary outcome performed after censoring individuals' follow-up on the date when they received levothyroxine therapy showed that during a median follow-up of 4.3 and 3.8 years, respectively, treated vs untreated younger and older individuals had similar risks of incident IHD events (HR, 0.87; 95% CI, 0.59-1.23; and HR, 1.12; 95% CI, 0.90-1.46; respectively). The HRs for IHD events were also analyzed after excluding individuals who had an IHD event within 6 months of starting levothyroxine therapy (n = 16), and HRs for IHD events remained similar in both age groups (data not shown). Also, we investigated the primary outcome by only including individuals who had persistent SCH during the full follow-up period in the untreated group and by further excluding individuals who commenced treatment with levothyroxine after progression to overt hypothyroidism. This approach demonstrated that the HR for IHD events (99 events in 2367 individuals) was 0.63 (95% CI, 0.42-0.94) in the 40 to 70–year-old group and 1.06 (95% CI, 0.91-1.74) in the older than 70–years age group (n = 106 events in 1079 people). Finally, to look for a biologically plausible gradation of the levothyroxine effect, we analyzed outcomes in relation to median baseline serum thyrotropin levels (6.6 mIU/L). This approach revealed that, in the 40 to 70–years group, compared with untreated individuals with SCH (referent HR of 1.0), treatment with levothyroxine reduced the risk of IHD events (HR, 0.62; 95% CI, 0.39-0.96; in those with thyrotropin levels <6.6 mIU/L; and HR, 0.48; 95% CI, 0.26-0.88; in those with thyrotropin levels ≥6.6 mIU/L; P = .007 for trend). In comparison, in the group older than 70 years, treated individuals with SCH who had a thyrotropin level less than 6.6 mIU/L at baseline had an HR of 1.02 (95% CI, 0.66-1.82), and those with a thyrotropin level of 6.6 mIU/L or higher had an HR of 1.19 (95% CI, 0.74-1.8) (P for trend = .08).