Cities are places of extremes where problems come in only large or super size: everyday ills are magnified, poverty is concentrated, and personal freedom readily turns into licence. For public health, they are the miner’s canary. Where cities lead, the rest of society follows.

Cities are also increasingly where most people live. As David Wilson of the World Bank reminded the inaugural City Health conference last week, in 1950 only 30% of the world’s population lived in urban areas. By 2050 it will have risen to 70%. The urban milieu that most of them will inhabit, he said, will be crowded, polluted, and unsafe—an environment that discourages exercise and exacerbates behaviours such as unhealthy eating, smoking, and alcohol and drug misuse. Fortunately, cities are also the engines of opportunity where new ideas emerge, where cooperative action is more easily established, and where wealth is generated.

The City Health conference, held in the Guildhall in the City of London on 22-23 October, aimed to identify public health threats through the concentrating lens of city life. Organised by the London Drug and Alcohol Policy Forum, it was the first of a series, with Glasgow already lined up to host next year’s event. The conference coincides with a fundamental change in the organisation of public health in England that will make local authorities responsible for its delivery under the guidance of a new body, Public Health England.

Like so many institutions in England, Public Health England will be run by a Scot, Duncan Selbie, who may have more to say in Glasgow than he did in London. The organisation is barely on its feet so he was light on specifics. But he did …