Secondhand smoke bad for brain?

"People who are exposed to secondhand smoke may be more likely than their peers to have cognitive impairment, a new study shows. The study, published in the advance online edition of BMJ, doesn't prove that secondhand smoke exposure causes cognitive impairment. But it does show that cognitive impairment was more common among nonsmokers and former smokers with high levels of cotinine, a nicotine-related chemical, in their saliva samples. The study included 4,809 adults 50 and older in England. They provided saliva samples and took various tests of mental skills, including memory and attention, between 1998 and 2002. Participants were considered cognitively impaired if their overall test score was in the bottom 10% of the group" - webMD