Smoking's impact on the immune system could last for up to 15 years after quitting: study

Smoking has harmful effects on the immune system, even long after you've quit, reports a study from the Institut Pasteur. Image: Solid photos / Shutterstock©

From cancer and cardiovascular disease to nutrient deficiencies and infertility, smoking has many harmful effects on health, some of which are still little-known. A new study reveals that smoking may have a long-term impact on the immune system. These harmful effects could even persist "for 10 to 15 years" after smoking cessation, scientists report.

The immune system's response to microbial attacks can vary considerably from one individual to another. While certain factors are known to influence these immune responses, such as age, gender and even genetics, others are less well known. Such is the case with smoking, a factor that a team of researchers at France's Institut Pasteur has been investigating. They based their study on the Milieu Intérieur cohort, which seeks to identify and evaluate the genetic and environmental factors likely to modify immune responses.

"While certain factors such as age, sex and genetics are known to have a significant impact on the immune system, the aim of this new study was to identify which other factors had the most influence," explains Darragh Duffy, Head of the Translational Immunology Unit at the Institut Pasteur, and last author of the study, quoted in a news release. For the purposes of their research, the scientists took blood samples from the 1,000 healthy participants aged between 20 and 70 in the Milieu Intérieur cohort, and subjected these to numerous microbes, to observe how their immune systems reacted. They did this by measuring levels of secreted cytokines, proteins involved in the immune system's defensive response.

Published in the journal, Nature, the study sought to determine which of the variables under investigation had the greatest influence on immune response, including body mass index, smoking, sleep, physical activity, vaccination and childhood diseases. The research identified three variables that were more influential than the others, one of which was smoking. A factor which, according to Darragh Duffy, "could be equal to that of age, sex or genetics" on certain immune responses. The scientists not only observed a greater inflammatory response in smokers, but also an impairment in the activity of cells involved in immune memory.

Also read: Big tobacco's environmental impact is 'devastating': WHO

"A comparison of immune responses in smokers and ex-smokers revealed that the inflammatory response returned to normal levels quickly after smoking cessation, while the impact on adaptive immunity persisted for 10 to 15 years. This is the first time it has been possible to demonstrate the long-term influence of smoking on immune responses," says Darragh Duffy. The scientific team explains this phenomenon by epigenetic mechanisms, i.e. reversible changes in gene expression linked to immune defenses.

These findings could lead to a better understanding of the impact of smoking on the immunity of both healthy people and those with various diseases or medical conditions. They also demonstrate the importance of quitting smoking as soon as possible. Moreover, a recent Canadian study, which looked at the impact of smoking cessation on life expectancy, rather than immunity, showed that benefits occurred rapidly and at any age.