Original research conducted by Yoneda and Watanabe, (1997) measured the response rates of pilots who were habitual smokers' at an altitude of 7,620 meters (25,000 ft). Their conclusions showed that smokers' were slightly resistant to altitude hypoxia because of their affinity toward anemic (hypemic) hypoxia brought about by increased carboxyhemoglobin levels due to habitual smoking.
Both studies concluded that the smokers' performed better in the early portion of'the studies while both cognitive and motor response rates deteriorated with pro- longed exposure to high altitudes.
http://docs.lib.purdue.edu/cgi/viewc...&context=jhpee
Being a smoker can also delay the onset of AMS.