If you quit smoking at 35, you can live 8 more years. But what if you are 75?

Because smoking is linked to cancer, stroke, heart disease and lung disease, quitting campaigns have been urging people to quit smoking as a way to improve their health. But the focus is mainly on getting young people to quit smoking "early". A new study finds that whether you quit smoking at age 35 or 75, you can add years to your life. The findings prove that people are never too old to benefit from quitting smoking.

New research from the University of Michigan School of Public Health finds that no matter how old you are when you quit smoking, you'll live longer.

Dr. Thuy Le, who conducted the study with Drs. David Mendez and Dr. Kenneth Warner, said: "Over the past decade, we have seen a significant decline in smoking rates among young people. However, smoking rates among older adults have remained stagnant and, to our knowledge, there have been no studies that have confirmed that quitting smoking is beneficial for them. We wanted to show that quitting smoking can be beneficial for people of any age and provide [motivation] for older adults who smoke to quit."

The researchers calculated age-specific mortality rates by smoking status (never smokers, current smokers, and former smokers who have quit) using relative risks of all-cause mortality from a range of U.S. national data sources. This information is used to create "life tables" showing how much life people can expect every 10 years between the ages of 35 and 75.

They found that compared with people who had never smoked, current smokers who continued to smoke as adults until age 35, 45, 55, 65 or 75 would have an average life expectancy reduction of 9.1, 8.3, 7.3, 5.9 and 4.4 years respectively if they continued to smoke for the rest of their lives. However, if they quit smoking at each of the above ages, they would avoid an average of 8.0 years, 5.6 years, 3.4 years, 1.7 years and 0.7 years of life lost respectively. Among those who quit smoking at age 65, the chance of gaining at least one year of life was 23.4%; among those who quit smoking at age 75, the chance of gaining at least one year of life was 14.2%. These are pretty good opportunities.

In addition, the data also showed that nearly 10% of people who quit smoking at the age of 65 lived at least 8 years longer than those who continued to smoke, while 8% of people who quit smoking at the age of 75 lived at least 4 years longer.

"The benefits of quitting smoking are not limited to young and middle-aged smokers, this study shows that they also apply to older adults," Warner said. "While the benefits of quitting may be lower in absolute terms for older adults, they represent a large proportion of an individual's remaining life expectancy."

The researchers hope clinicians will use this study as scientific evidence to persuade their patients, especially older smoking patients, to quit smoking.

The study was published in the American Journal of Preventive Medicine.