Nicotine is very toxic to your body. Cigarettes can have up to 3,500 different toxins in addition to nicotine.
Nicotine causes vasoconstriction. The “vaso” is Latin for blood vessel and “constriction” means to get smaller. When you are using nicotine or are even around other people that are smoking and have third hand smoke on your clothes that can cause your blood vessels to undergo vasoconstriction. The result is less blood being delivered to the area where the fracture has occurred. The blood flow is very important to help heal the fracture as it brings in stem cells and other growth factors.
Vaping is just as bad as smoking if you are vaping with a product that has nicotine.
Studies have shown that if you are consuming nicotine you can increase the time to heal the fracture by double and sometimes a fracture will just not heal. In that case, you will need to undergo surgery to get the broken bone to heal. Most surgeons will require you to stop smoking before they would undergo surgery to help heal a bone that has not healed because of nicotine intake.