Passing on the flame do mega sports events promote health behaviours?

To justify billion-dollar public expenditures on mega sports events, proponents often suggest lasting improvements in health behaviours among the general public. To estimate the returns to health behaviours from hosting the 2012 London Olympics, we collected panel data on more than 19, 000 respondents across two European capitals, London and Paris, between 2011 and 2013. Using a difference-in-differences design with Paris as counterfactual, we find an increase in physical activity by six percentage points among the inactive, from a baseline of 34%. Activation, however, lasts only for about 100 days. Although we also find suggestive evidence for reduced alcohol and tobacco consumption during the event, a cost-benefit analysis suggests that staging mega sports events is not a cost-effective policy to promote lasting health behaviour change.