With the continued spread of COVID‐19 globally, it is crucial to identify the potential risk or protective factors associated with COVID‐19. Here, we performed genetic correlation analysis and Mendelian randomization analysis to examine genetic relationships between COVID‐19 hospitalization and 405 health conditions and lifestyle factors in 456 422 participants from the UK Biobank. The genetic correlation analysis revealed 134 positive and 65 negative correlations, including those with intakes of a variety of dietary components. The MR analysis indicates that a set of body fat‐related traits, maternal smoking around birth, basal metabolic rate, lymphocyte count, peripheral enthesopathies and allied syndromes, blood clots in the leg, and arthropathy are causal risk factors for severe COVID‐19, while higher education attainment, physical activity, asthma, and never smoking status protect against the illness. Our findings have implications for risk stratification in patients with COVID‐19 and the prevention of its severe outcomes.