Quitting smoking is probably the single greatest lifestyle change you can make to improve your long-term health. Every time you puff on a cigarette, you risk damaging nearly every organ in your body.

Smoking is a major factor in the development of diseases such as heart disease, cancer, pneumonia and emphysema. Smoking also affects short-term health. For example, smoking damages the immune system, making you more vulnerable to infections.

It can be difficult to quit smoking once you've started. However, kicking the habit yields tremendous health benefits. Some of these improvements begin almost immediately while others kick in over the next year. They include:

• Drop in heart rate and blood pressure. When you smoke, the nicotine inside the cigarette causes your blood vessels to constrict. This impairs circulation and triggers a spike in both heart rate and blood pressure. Within 20 minutes of quitting smoking, both heart rate and blood pressure begin to improve. Further significant improvement in circulation may continue over the next two weeks to three months.
  
  
• Reduction in carbon monoxide level inside the blood. Carbon monoxide (CO) is an odorless, colorless gas that is toxic and potentially life-threatening in high doses. Cigarette smoke contains CO, and smokers tend to have CO-saturated blood, which impairs the blood's ability to carry oxygen. This makes exercise more difficult. About 12 hours after you quit smoking, the carbon monoxide level in your blood returns to normal levels.
  
  
• Increase in lung function. Smoking damages the airways and small air sacs within the lungs. This leads to chronic coughing and wheezing. Eventually, it may become difficult to breathe. Your lung function may begin to improve anywhere from two weeks to three months after you quit. Coughing and shortness of breath may begin to subside. Tiny hair-like structures known as cilia may recover inside the lungs, allowing you to better handle mucus that builds up. This helps keep the lungs clean and reduces the risk of infection.
  
  
• Reduced risk of coronary heart disease. Smoking is closely linked with coronary heart disease, which causes more deaths in the United States than any other condition. If you smoke, your risk of developing this illness increases by two to four times. However, one year after you quit smoking, your risk drops to half that of a smoker.