Smoking can be thought of as a slow way of killing you. Cigarettes are full of toxic poisons. Nicotine itself is a toxin, a fertiliser like DDT. Packet cigarettes contain thousands of poisons including arsenic, benzene and carbon monoxide. Our bodies are well equipped to deal with poisons in small amounts and on a temporary basis. This makes us adaptive and is useful for our survival as a species, but make no mistake about it, if you keep introducing these poisons into your body long enough, they will kill you.
If you think of your life expectancy plotted on a graph, your decline towards death will be much steeper than a non-smoker. But not only that, your quality of life will suffer and will not be as good as a non-smoker. The health risks of smoking are more severe the older you are, particularly when you get into your 50s, but it is never too late to give up and start to improve your health.
For further ideas and advice and ways to stop smoking, visit the substantial resources section of this site - Stop Smoking Resources