INTRODUCTION: Cognitive ability is substantially hereditary and predicts socioeconomic status (SES), health behaviours, physical health, and longevity. The robustness and mediation of the CA – mortality association is... [ view full abstract ]
INTRODUCTION: Cognitive ability is substantially hereditary and predicts socioeconomic status (SES), health behaviours, physical health, and longevity. The robustness and mediation of the CA – mortality association is however insufficiently understood. Our previous findings suggest that the effect of early-in-life CA on later-in-life mortality also holds for post MI male patients, and that a portion of this effect likely flows through a range of different but interlinked factors. Here, we examined the association of CA and five-year post-MI all-cause mortality with respect to attenuation by (a) long-term lifestyle risk factors, and (b) short-term cardiac rehabilitation participation post MI, and (c) mediation through education and income.
METHODS: This decennial (2006-2015) observational cohort study used the CA exposure estimated at 18-20 years of age from Mandatory Conscript Registry data for 13093 first MI males (mean age at hospital admission = 52.5 years). No patient was lost to follow-up in the Cause of Death Registry for the five-year all-cause mortality post-MI outcome. The SWEDEHEART registries for acute coronary events (RIKS-HIA), and secondary prevention (SEPHIA) provided data on background and clinical variables. Statistics Sweden supplied data on educational attainment and income. After multivariable imputation of covariates, Cox regression and survival curves were used to estimate crude and adjusted associations. Ordinal and binomial logistic regression were applied for the mediation and outcome model, respectively, and combined in mediation analysis.
RESULTS: During a mean follow up of 3.6 years, 311 deaths occurred. Compared to 1,439 patients with low IQ, (Stanine 1-2.75), 10,822 with medium (3-7) and 832 with high CA (7.25-9) were associated with a lower risk of mortality (HR [95% CI] = 0.55 [0.41, 0.74] and 0.45 [0.25, 0.81], respectively). With adjustment for long-term lifestyle factors, the IQ – mortality association was attenuated (0.61 [0.45, 0.82]; 0.55 [0.30, 1.00]), and with further adjustment for short-term cardiac rehabilitation participation it was further attenuated (0.64 [0.48, 0.86]; 0.61 [0.34, 1.11]). SES partially mediated the CA – mortality effect through education (proportion mediated = 12.5%) and income (19.6%), with a controlled direct effect of CA on mortality being dominant in both models.
CONCLUSION: Mortality after the first, non-fatal myocardial infarction (MI) is predicted by early-in-life cognitive ability (CA). The CA – mortality association was found to be partially attenuated by (a) lifestyle risk factors, (b) cardiac rehabilitation participation, and (c) partially mediated through educational attainment and income.
