Insomnia is an important public health problem affecting ≈10% to 30% of the general population.1 Evidence from observational studies indicates that insomnia is associated with an increased risk of cardiovascular disease (CVD). However, whether the association is causal is unknown because observational studies are hampered by reverse causation bias and residual confounding. Self-reported insomnia may be correlated with confounding factors, such as socioeconomic position, chronic illness, and lifestyle factors that may bias the observational findings.