[moggy]

I think it is one of those trendy studies. There are multiple factors likely to influence whether somone develops asthma.

Fast food outlets are pretty well always in cities. Cities in general usually have a high level of asthma in children, often credited polution from cars (another study that comes to mind is one that showed the closer that you lived to a main road the greater risk a child was of getting it). Also as with most illnesses there is often a big genetic factor Japanese are obviously from a different genetic pool to Europeans.

A correllation study like this proves nothing. It shows no causuality at all

perhaps kids who eat a lot of fast food in general have a bad diet (eg your chav culture), or that kids in inner cities get less exercise, it could be anything.

There is a very high correllation between the amount of ice cream sold in a day and your likelihood of drowning. One does not cause the other, it just happens that they are both influenced by how nice a day it is.