Smoking a single cigarette takes about 20 minutes off a person’s life, researchers at University College London have found.

Men lose 17 minutes of life with every cigarette they smoke while a woman’s life is cut short by 22 minutes each time, the experts estimated. 

“People generally know that smoking is harmful but tend to underestimate just how much,” Sarah Jackson, a principal research fellow at UCL’s alcohol and tobacco research group said. “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.”

The study was commissioned by the UK Department of Health using the latest data from the British Doctors Study, which began in 1951 and the Million Women Study, which has tracked women’s health since 1996.

In 2000 an assessment published in the British Medical Journal found that on average a single cigarette reduced life expectancy by about 11 minutes, half the new findings.   

“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 newspaper. “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 of the study stressed that smokers must quit completely to get the full benefits of health and life expectancy.