obviosuly it does....it has been proved
check worldometers.info for details on smoking to see how many people are dying because of smoking, but some people cannot live without smoking because of medical conditions.
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not sure, though i read another answer on this website that says you lose 7 minutes of your life for every cigarette you smoke
Due to recent studies it usually takes off anywhere from about 10 minutes up to 12 minutes off of your life.
It's impossible to say and any attempt to quantify it is pure conjecture, based on highly suspect "junk science".