Abstract
Background Causes of the association between lower cognitive ability and poorer health remain unknown, but may reflect a shared genetic aetiology as indicated by previous research. This study examines the causal genetic associations between cognitive ability and physical health outcomes.
Method We carried out Mendelian randomization analyses using the inverse variance weighted method to test for causality between later life cognitive ability, educational attainment (as a proxy for cognitive ability in youth), BMI, height, systolic blood pressure, coronary artery disease, and type 2 diabetes in the UK Biobank sample (N = 112 151). Sensitivity analyses were performed using MR-Egger regression.
Results BMI, systolic blood pressure, coronary artery disease and type 2 diabetes showed negative associations with cognitive ability, while height was positively associated with cognitive ability. The Mendelian randomization analyses provided no evidence for a casual association from health to cognitive ability. In the other direction, higher educational attainment predicted lower BMI, systolic blood pressure, coronary artery disease, type 2 diabetes, and taller stature. The Mendelian randomization analyses indicated partly causal associations from educational attainment to health, however when adjusting for bias using the MR-Egger regression, these effects disappeared.
Conclusions The lack of consistent evidence for causal associations between cognitive ability, educational attainment, and physical health could be explained by violations of the Mendelian randomization assumptions, including biological pleiotropy.
Key messages
Cognitive ability and physical health outcomes are positively associated.
Mendelian randomization analyses indicated that educational attainment influenced physical health outcomes.
Sensitivity analyses, using MR-Egger regression, indicated that these associations were biased due to violations of the Mendelian randomization assumptions.
