"Long before it's in the papers"
June 03, 2013

RETURN TO THE WORLD SCIENCE HOME PAGE

Quitting smoking may extend life 10 years

Oct. 28, 2012
Courtesy of The Lancet
and World Science staff

Quit­ting smok­ing early pro­longs life­span by an aver­age of about 10 years, a big­ger ben­e­fit than was pre­vi­ously un­der­stood, ac­cord­ing to a study of 1.3 mil­lion U.K. wom­en.

The sci­en­tists say that oth­er new re­search sug­gests si­m­i­lar ef­fects in men.

Brit­ish re­search­ers re­cruited 1.3 mil­lion wom­en were to a study be­tween 1996 and 2001, at ages 50 to 65 years. Par­ti­ci­pants filled out a ques­tion­naire about lifestyle, med­i­cal and so­cial fac­tors and were resur­veyed by mail three years lat­er. Wom­en were traced for an av­er­age of 12 years from when they joined. The find­ings were pub­lished in the med­i­cal jour­nal The Lan­cet on Oct. 27.

In­i­tial­ly, 20 per­cent of the study par­ti­ci­pants were smok­ers, 28 per­cent were ex-smok­ers, and 52 per­cent had nev­er smoked. Those who were still smok­ers three years lat­er were found to be nearly three times as likely as non-smok­ers to die over the next nine years, even though some re­duced their risk by stop­ping smok­ing dur­ing this pe­ri­od. 

The three­fold death rate ra­tio means that two-thirds of all deaths of smok­ers in their 50s, 60s, and 70s are caused by smok­ing, as most of the dif­fer­ence be­tween smok­ers and non-smok­ers came from smok­ing-related dis­eases such as lung can­cer, chron­ic lung dis­ease, heart dis­ease, or stroke, the re­search­ers said.

The risks among smok­ers in­creased steeply with amount smoked, al­though even for those who smoked just one cig­a­rette a day at the start of the stu­dy, mor­tal­ity rates were dou­ble those for non-smok­ers.

Both the haz­ards of smok­ing and, ac­cord­ing­ingly, the ben­e­fits of stop­ping are big­ger than pre­vi­ous stud­ies have sug­gested, the in­ves­ti­ga­tors said. Smok­ers who stopped around age 30 were found to avoid 97 per­cent of their ex­cess risk of prem­a­ture death, and al­though se­ri­ous ex­cess haz­ards re­mained for dec­ades among those who smoked un­til age 40 be­fore stop­ping, the ex­cess haz­ards among those who con­tin­ued smok­ing af­ter age 40 were ten times big­ger.

“If wom­en smoke like men, they die like men – but, wheth­er they are men or wom­en, smok­ers who stop be­fore reach­ing mid­dle age will on av­er­age gain about an ex­tra ten years of life,” said study co-author Rich­ard Pe­to, at the Uni­vers­ity of Ox­ford, UK. “Both in the UK and in the USA, wom­en born around 1940 were the first genera­t­ion in which many smoked substanti­al num­bers of cig­a­rettes through­out adult life. Hence, only in the 21st cen­tu­ry could we ob­serve di­rectly the full ef­fects of pro­longed smok­ing, and of pro­longed cessa­t­ion, on prem­a­ture mor­tal­ity among wom­en.”

The au­thors wrote that they found “the pro­por­tion­al ex­cess risk in smok­ers was more marked than in many pre­vi­ous stud­ies, but re­cently up­dat­ed anal­y­ses of 21st cen­tu­ry mor­tal­ity in six smaller co­horts of U.S. smok­ers now sug­gest, in ag­gre­gate, si­m­i­lar haz­ards from smok­ing and ben­e­fits of stop­ping, as does a re­cent study in Jap­a­nese men and wom­en.”

As for their own stu­dy, Pe­to and col­leagues wrote fur­ther that “al­though the rel­a­tive risks for the ef­fects of pro­longed smok­ing on par­tic­u­lar dis­eases can­not be gen­er­al­ised ex­actly to popula­t­ions with very dif­fer­ent back­ground rates of those dis­eases, they should be ap­prox­i­mately gen­er­al­isable to many (though not all) coun­tries where wom­en smoke.”

The re­search was pub­lished to mark the 100th an­ni­ver­sa­ry of the birth of Sir Rich­ard Doll, one of the first peo­ple to iden­ti­fy the link be­tween lung can­cer and smok­ing.

* * *

Quitting smoking early may prolong lifespan by 10 years or more, a bigger benefit than was previously understood, according to a study of 1.3 million U.K. women. The scientists say that other new research suggests similar effects in men. British researchers recruited 1.3 million women were to a study between 1996 and 2001, at ages 50 to 65 years. Participants filled out a questionnaire about lifestyle, medical and social factors and were resurveyed by mail three years later. Women were traced for an average of twelve years from the time they first joined. The findings were published in the medical journal The Lancet on Oct. 27. Initially, 20% of the study participants were smokers, 28% were ex-smokers, and 52% had never smoked. Those who were still smokers three years later were found to be nearly three (2.97) times as likely as non-smokers to die over the next nine years, even though some reduced their risk by stopping smoking during this period. The threefold death rate ratio means that two-thirds of all deaths of smokers in their 50s, 60s, and 70s are caused by smoking, as most of the difference between smokers and non-smokers came from smoking-related diseases such as lung cancer, chronic lung disease, heart disease, or stroke, the researchers said. The risks among smokers increased steeply with amount smoked, although even for those who smoked just one cigarette a day at the start of the study, mortality rates were double those for non-smokers. Both the hazards of smoking and, correspondingly, the benefits of stopping are bigger than previous studies have suggested, the investigators said. Smokers who stopped around age 30 were found to avoid 97% of their excess risk of premature death, and although serious excess hazards remained for decades among those who smoked until age 40 before stopping, the excess hazards among those who continued smoking after age 40 were ten times bigger. “If women smoke like men, they die like men – but, whether they are men or women, smokers who stop before reaching middle age will on average gain about an extra ten years of life,” said study co-author Richard Peto, at the University of Oxford, UK. “Both in the UK and in the USA, women born around 1940 were the first generation in which many smoked substantial numbers of cigarettes throughout adult life. Hence, only in the 21st century could we observe directly the full effects of prolonged smoking, and of prolonged cessation, on premature mortality among women.” The authors wrote that they found “the proportional excess risk in smokers was more marked than in many previous studies, but recently updated analyses of 21st century mortality in six smaller cohorts of U.S. smokers now suggest, in aggregate, similar hazards from smoking and benefits of stopping, as does a recent study in Japanese men and women.” As for their own study, Peto and colleagues wrote further that “although the relative risks for the effects of prolonged smoking on particular diseases cannot be generalised exactly to populations with very different background rates of those diseases, they should be approximately generalisable to many (though not all) countries where women smoke.” The research was published to mark the 100th anniversary of the birth of Sir Richard Doll, one of the first people to identify the link between lung cancer and smoking.