Dr. Halpern said the Michigan study specifically examined the cancer risk in relation to the ages at which people quit.
The mean age of 900,000 participants at the beginning of the study was 57. About half had never smoked and one-quarter were former smokers.
The average male smoker in the study began smoking at about age 17 and smoked 26 cigarettes a day; the average female began smoking a year later and smoked 22 cigarettes a day.
The researchers found that fewer than 50 male nonsmokers and fewer than 30 female nonsmokers in 100,000 died of lung cancer by the age of 75. By contrast, 1,250 men in 100,000 who continued to smoke and 550 women in 100,000 who continued to smoke died of lung cancer by the age of 75. Death Rate and Age
The death rate at age 75 for former smokers depended on the age at which people quit smoking, Dr. Halpern said.
Among former smokers who quit in their 30's, the study found that 90 men and 55 women in 100,000 died of lung cancer by age 75. For those who quit in their 40's, the number of people who died of the disease rose to 150 men and 80 women.
As people quit smoking later in life, the study found, they tended to die more frequently from lung cancer. For those who quit by 54, there were 240 deaths among men and 125 among women; by 59, there were 340 deaths among men and 170 for women, and by 64, there were 500 deaths among men and 270 among women.
http://www.nytimes.com/1993/03/21/us...kers-quit.html
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