What's bad for the lungs may also be bad for the brain. Emerging evidence suggests that breathing in polluted air is tied to a higher risk of developing dementia. For many city residents, that's impossible to avoid, but other substances we inhale are more within our control. An analysis of self-reported health data in the United States, collected as part of a decades-long study , has now found that quitting smoking in later life is tied to a 16 percent lower risk of dementia. In fact,