Smokers are being urged to kick the habit for 2025 after a fresh assessment of the harms of cigarettes found they shorten life expectancy even more than doctors thought.

Researchers at University College London found that on average a single cigarette takes about 20 minutes off a person’s life, meaning that a typical pack of 20 cigarettes can shorten a person’s life by nearly seven hours.

According to the analysis, if a smoker on 10 cigarettes a day quits on 1 January, they could prevent the loss of a full day of life by 8 January. They could boost their life expectancy by a week if they quit until 5 February and a whole month if they stop until 5 August. By the end of the year, they could have avoided losing 50 days of life, the assessment found.

“People generally know that smoking is harmful but tend to underestimate just how much,” said Dr Sarah Jackson, a principal research fellow at UCL’s alcohol and tobacco research group. “On average, smokers who don’t quit lose around a decade of life. That’s 10 years of precious time, life moments, and milestones with loved ones.”

Smoking is one of the world’s leading preventable causes of disease and death, killing up to two-thirds of long-term users. It causes about 80,000 deaths a year in the UK and a quarter of all cancer deaths in England.

The study, commissioned by the Department of Health, draws on the latest data from the British Doctors Study, which began in 1951 as one of the world’s first large studies into the effects of smoking, and the Million Women Study, which has tracked women’s health since 1996.

While an earlier assessment in the BMJ in 2000 found that on average a single cigarette reduced life expectancy by about 11 minutes, the latest analysis published in the Journal of Addictionnearly doubles the figure to 20 minutes – 17 minutes for men and 22 minutes for women.

“Some people might think they don’t mind missing out on a few years of life, given that old age is often marked by chronic illness or disability. But smoking doesn’t cut short the unhealthy period at the end of life,” Jackson told the Guardian. “It primarily eats into the relatively healthy years in midlife, bringing forward the onset of ill-health. This means a 60-year-old smoker will typically have the health profile of a 70-year-old non-smoker.”

Although some smokers live long lives, others develop smoking-related diseases and even die from them in their 40s. The variation is driven by differences in smoking habits such as the type of cigarette used, the number of puffs taken and how deeply smokers inhale. People also differ in how susceptible they are to the toxic substances in cigarette smoke.

The authors stress that smokers must quit completely to get the full benefits to health and life expectancy. Previous work has shown there is no safe level of smoking: the risk of heart disease and stroke is only about 50% lower for people who smoke one cigarette a day compared with those who smoke 20 a day. “Stopping smoking at every age is beneficial, but the sooner smokers get off this escalator of death the longer and healthier they can expect their lives to be,” they write.

The Department of Health said smokers could find advice, support and resources on the NHS Quit Smoking app and the online Personal Quit Plan, which tailors its advice to individual’s preferences.

Prof Sanjay Agrawal, a special adviser on tobacco at the Royal College of Physicians, said: “Every cigarette smoked costs precious minutes of life, and the cumulative impact is devastating, not only for individuals but also for our healthcare system and economy. This research is a powerful reminder of the urgent need to address cigarette smoking as the leading preventable cause of death and disease in the UK.”

The Guardian, UK