An age limit on London taxis has also been implemented, which has removed 6,000 of the oldest and most polluting vehicles from the roads, and there has been an investment into reducing pollution from buses. Khan has previously said that "tackling London’s filthy air" is one of his main priorities as mayor, but any progress will be gradual. So, if you're an outdoor runner or regularly walk long distances around the capital – especially if you experience symptoms such as a cough or sore throat – it might be worth considering working out indoors or using public transport to get around for the time being. High and very high levels of pollution can cause asthma sufferers to need their inhaler more and can increase the risk of respiratory diseases , including asthma and lung cancer. However, it won't be possible for everyone to modify their routine and many people training for the London Marathon are understandably frustrated by the warning, with some suggesting the Mayor should go further to cut pollution.