Smoking shortens life by almost ten years not just four, says a new study. The good news is that smokers can decrease the risk of dying early by quitting smoking, preferably before they turn 35.

Previous studies said that smoking takes around four years off a person's life. However, the new study conducted by researchers from Oxford and Japan has shown that smoking can take away a decade from a smoker's life.

The study was conducted on people who lived in Hiroshima and Nagasaki in Japan during the 1950s and the results were independent of the effects of radiation on these people.

The study results are based on information obtained from Lifespan Study conducted in the 1950s to analyze the effects of radiation on peoples' lives. The study had tracked over 100,000 people. But, may were found to have very low levels of radiation exposure. The data on these people provides information about the effects of other factors on life-expectancy, including smoking.

The present study analyzed the effects of smoking in 68,000 men and women, who have been followed now for almost 23 years.

The study found that both men and women, who started smoking early (before age 20 or so) had higher risk of dying early than those who smoked after they reached adulthood. Previous studies in Japan had only focused on population groups that began smoking later in life and so the risk of early death was lower. The new study shows that the risk of early death due to smoking doubles for people who smoke at an early age compared to people who don't smoke.

Researchers also found that men and women who gave up smoking before they turned 35 lived longer when compared to life-long smokers. Those who quit smoking after 40 years somewhat lowered their risk of dying early.

According to Centers for Disease Control and Prevention, 45.3 million people, or 19.3% of all adults, in the United States smoke cigarettes. The agency also says that smoking kills an estimated 443,000 people, or 1 of every 5 deaths, in the United States each year.