Women smokers who quit young cut death risk

“Women smokers who quit before 30 cut death risk by 97%”, The Guardian reports. It goes on to warn that ‘women who smoke into middle-age have three times the death rate of non-smokers and risk dying at least 10 years early’.

The news is based on the results of an impressive study that followed 1.2 million women aged from 50 to 69 years old, for an average of 12 years to determine the full effects of prolonged smoking and quitting on women in the UK.

The study authors report that smoking prevalence in young women did not peak until the 1960s, so the full risks of smoking can only be seen now. They found that women who reported smoking at the start of the study (recruitment 1996-2001), had an almost tripled risk of death from any cause compared to women who had never smoked.

The good news is that permanently quitting smoking reduced their risk of death compared to women who continued smoking. The researchers noticed a ‘sooner-the-better’ pattern – women who quit smoking before the age of 30 reduced their risk of having a smoking-associated death by a massive 97%. Even women who quit later in life, such as around the age of 50, still experienced a large reduction in ‘excess’ mortality risk associated with smoking (72%).

The study should not be interpreted along the lines of ‘it’s okay to smoke until I am 30, and then I can quit’, as the results clearly found that smoking at any age, for any duration, increased the risk of premature death.

However, it does show that quitting at any age, brings important health benefits and that it is never too late.

Where did the story come from?

The study was carried out by researchers from the University of Oxford and was funded by Cancer Research UK, the British Heart Foundation, and the Medical Research Council.

The study was published in the peer-reviewed medical journal The Lancet. This article has been made available free of charge (open access).

This story was widely reported, and the coverage by the media was both accurate and appropriate.

The Guardian also highlighted the fact that the study was published a day before the 100th anniversary of the birth of Sir Richard Doll, the influential epidemiologist whose landmark research helped establish the link between smoking and lung cancer.

What kind of research was this?

This was a prospective cohort study. It aimed to determine the full effects of prolonged smoking, and of prolonged cessation, on the death-rates of women in the UK.

A prospective cohort study is the ideal study design to answer this question about how smoking impacts on mortality rates. However, the study design does have a number of limitations: it can only suggest associations, and cannot prove a direct cause-and-effect link between smoking and health outcomes. For example, in this study smokers were more likely than non-smokers to live in deprived areas, drink more alcohol, and do less exercise, all of which have been linked to poor health outcomes. The researchers accounted for these factors in their analyses, but there could be other factors that have not been accounted for.

However, the link between smoking and a number of diseases, such as lung cancer and heart disease has already been well-established.

What did the research involve?

Between 1996 and 2001, 1.2 million UK women aged from 50 to 69 years old, without a history of smoking-related diseases, were recruited into the Million Women Study – which is an ongoing cohort study designed to provide more information on various issues relating to women’s health.

The women were asked at study entry whether they were current or ex-smokers. If they were smokers, they were asked how many cigarettes they currently smoked, and at what age they had started smoking. All women were also asked questions about their lifestyle, medical history, and sociodemographic status.

At the start of the study:

20% of the women were current smokers
28% were ex-smokers
52% were never smokers

Women were then asked about their smoking habits and lifestyle again, three years and eight years later. Women who were ex-smokers at both study entry and the three-year re-survey and had stopped before the age of 55 years were categorised as ex-smokers and were further analysed by the age they had stopped smoking. All women were followed through national mortality records until the 1st January 2011, on average for 12 years. The researchers then compared the risk of death in smokers, ex-smokers and never-smokers.

What were the basic results?

The researchers found, after adjusting for geographical region, age, and other factors including body-mass index, socioeconomic status, current alcohol intake, and exercise, that:

during the study, 6% of women had died, at an average age of 65 years
those smoking at the start of the study had almost three times the overall mortality rate of never smokers (mortality rate ratio 2.76, 95% confidence interval (CI) 2.71 to 2.81) during the 12-year follow-up, even though 44% of the baseline smokers had stopped smoking at the eight-year follow-up
in those reporting smoking at baseline and at the three-year re-survey, the mortality rate tripled compared to non-smokers (mortality rate ratio 2.97, 95% CI 2.88 to 3.07)
risks of death increased with earlier regular smoking, with those starting at age 15 years at greater risk than those who started only four years later
risk of death also increased with increasing number of cigarettes smoked per day; 12-year mortality was doubled, even for women smoking fewer than 10 cigarettes per day at the start of the study (rate ratio 1.98, 95% CI 1.91 to 2.04)
of the 30 most common causes of death, 23 were increased significantly in smokers. The majority of the excess mortality among smokers was from diseases that can be caused by smoking, for example lung cancer.
Ex-smokers who stopped permanently when they were aged between 25 and 34 (mean age 29 years), or aged between 35 and 44 (mean age 39 years) had respectively a 5% (borderline significant) or 20% increased risk of death during the nine remaining years of follow-up, compared to non-smokers (relative risk 1.05, 95% CI 1.00 to 1.11 and 1.20 95% CI 1.14 to 1.26, respectively). Therefore, although these populations are still at increased risk of death, it is only a fraction of the risk of continuing smokers. Stopping smoking before 40 years of age avoided 90% of the excess mortality associated with smoking, and before 30 years of age avoided 97% of the excess mortality
women who stopped aged between 45 and 54 (mean age 49, the eldest age group examined) were at 56% increased risk of death compared to non-smokers (relative risk 1.56 95% CI 1.49 to 1.64). However, quitting still avoided 72% of the excess mortality associated with smoking

How did the researchers interpret the results?

The researchers concluded that “among UK women, two-thirds of all deaths of smokers in their 50s, 60s and 70s are caused by smoking; smokers lose at least 10 years of lifespan. Although the hazards of smoking until 40 years of age and then stopping are substantial, the hazards of continuing are ten times greater. Stopping before age 40 years (and preferably well before age 40 years) avoids more than 90% of the excess mortality caused by continuing smoking; stopping before age 30 years avoids more than 97% of it”.

Conclusion

This large, well-designed cohort study followed 1.2 million women aged from 50 to 69 years for an average of 12 years, to determine the full effects of prolonged smoking and quitting on women in the UK.

The researchers found that women who reported smoking at the start of the study had almost three times the risk of death from any cause than women who had never smoked.

Also, the majority of the excess mortality among smokers was from diseases that can be caused by smoking, for example lung cancer.

Although women who had smoked were still at increased risk of death compared to non-smokers, permanently quitting smoking reduced their risk of death compared to women who continued smoking. Women who stopped before 30 years of age remained at (a borderline significant) 5% increased risk of death compared to non-smokers, but avoided 97% of the excess mortality associated with smoking. Women who stopped before 50 years of age remained at 56% increased risk of death compared with non-smokers, but avoided 72% of the excess mortality associated with smoking.

Although this type of study cannot prove that smoking or quitting caused the health outcomes observed, as it is possible that other factors could explain the associations seen, the link between smoking and a number of diseases has already been well established,

The researchers also accounted for a number of possible factors that could explain the associations seen. This study provides more information on the full effects of smoking on women. The results suggest, in line with general heath advice, that smoking increases the risk of death, and that ex-smokers remain at an increased risk of death compared to never smokers. However, quitting at any age is better than continuing smoking, and it is never too late to quit, whatever your age, to enjoy health benefits associated with stopping smoking.