2 things here :
As U surely know, the body (brain cells, lungs, etc) is damaged each time U smoke, so whether U do or do not actually smoke during a flight won't change this "damage" history. The worst, aviation-related, effect of smoking is that CO adheres to the protein haemoglobin in the red blood cells, which damges both the breathing process & the O2-CO2 chemical exchanges. This results in an early onset of hypoxia @ altitude.
In addition to that, if U actually smoke during the flight, not only does it damage the A/C system of the aircraft, but it also reduces your "g" tolerance. U will B more prone to airsickness.
MF