More than ten million Britons are at a higher risk of dementia because they live near a busy road, scientists have concluded. Those living in big cities are up to 12 per cent more likely to develop dementia as a result of traffic fumes, according to a study of more than six million people in Ontario, Canada. The closer people live to heavy traffic, the higher the risk. The scientists said that their findings were ‘of real public health significance’. They called for homes to be built further away from traffic, and for levels of traffic-related air pollution to be further reduced. Half the population of Ontario lives within 200 metres of a busy road, and 20 per cent within fifty metres: these figures are likely to be higher in Britain.