Just smoking one cigarette will reduce your life by 20 minutes?

Compiled by: Gong Zixin

Just one cigarette can shave about 20 minutes off a long-term smoker's lifespan, according to new research from behavioral scientists at University College London, who published an editorial in the journal Addiction outlining their study of lifespans among British smokers.

Smoking is one of the biggest preventable causes of disease, disability and premature death worldwide. There is a wealth of research showing the serious health consequences of smoking. Despite this, more than 6.5 million people living in the UK are still classed as current smokers. In this new study, the UCL team took a different approach to convincing people to quit - pointing out the harm caused by just one cigarette.

Back in 2000, an estimate published in the British Medical Journal (BMJ) suggested that smokers in the UK lose an average of 11 minutes of life for every cigarette they smoked. Now, the team has updated data, having made some important assumptions.

The researchers drew data from the British Doctors Study and the Million Women Study, calculating the impact of smoking on life expectancy down to the level of one cigarette for men and women. They found that among long-term smokers, one cigarette would shorten life expectancy by 17 minutes for men and 22 minutes for women.

They also found that data from both sources supported previous findings that the harms caused by smoking are cumulative and that the benefits of quitting depend on several factors, including current health, how long a person lives and how many cigarettes a day they smoke.

The research team further pointed out that the earlier a person quits smoking, the more cigarettes they avoid, and the longer they live. The overall benefits of quitting smoking can be divided into days, weeks, months, and even years. For example, not smoking for a week can prevent a day of life loss; doing so for a few weeks can prevent a full week of life loss. In other words, someone who smokes 10 cigarettes a day and quits on January 1, 2025, can prevent a day of life loss by January 8; prevent a week of life loss by February 20; prevent a month of life loss by August 5; and by the end of the year, 50 days of life loss can be avoided.

The research team also noted that quitting smoking at a relatively young age can reap greater benefits than quitting at an older age. For example, quitting smoking at age 40 has been shown to reduce the risk of dying from smoking-related diseases by up to 90%.

Studies have shown that the number of healthy years lost by smokers is generally about the same as the total number of life years lost. Thus, smoking primarily erodes relatively healthy middle age rather than shortening the end of life, which is often marked by chronic disease or disability. Thus, a 60-year-old smoker typically has the health of a 70-year-old nonsmoker.

As with the BMJ 2000 estimate, the study's updated figures come with some important caveats. First, these are averages across different populations and ages, with some smokers leading long and healthy lives while others die from smoking-related illnesses, even in their 40s. This variation is due to differences in smoking patterns (number of puffs, depth of inhalation, etc.), type of smoking, and individual susceptibility to toxicants in cigarette smoke.

Furthermore, the harm caused by each cigarette smoked varies across the lifespan. The health risks of smoking are not linear, and simply reducing smoking is not enough - you need to quit smoking completely to achieve the greatest benefits to your health and life. The age at which you start smoking may also play a role, and starting smoking at a young age may make you more susceptible to smoking-related diseases.

Evidence from mortality studies suggests that the earlier a person quits, the greater the benefit of quitting on life expectancy. Another caveat is that the researchers assumed that the number of cigarettes smoked per day is constant over life. Also, the ratio of tar to nicotine has fallen over the decades, and given that most of the harm from smoking comes from tar, exposure to the toxicant per cigarette may have decreased. If so, then our estimate of life years lost per cigarette would be a bit high, but the true number is likely to still be much higher than the 2000 estimate in the BMJ.

In summary, quitting smoking is beneficial at every age, but the earlier smokers quit, the longer and healthier they can expect to live, the researchers said.