Quitting cigarettes does not mean an immediate return to perfect health. Two recent studies show the lasting effects of smoking on health. Our immune system, in particular, seems to be more damaged than expected. “Smoking consistently modulates adaptive immunity,” concludes a study published this Wednesday in the journal Nature.
The work represents an important advance in understanding the harmful health effects of smoking, which according to the World Health Organization (WHO) kills about eight million people worldwide each year. It highlights a hitherto overlooked element: the adaptive immune system, which builds up with periodic infections, remains impaired for years after smoking cessation.
These findings are based on a sample of one thousand people. These were selected more than ten years ago as part of a project led by the Pasteur Institute in Paris, and their immunity has since been regularly studied through various tests, particularly blood tests. This type of project, called a cohort project, is very robust for assessing how health and metabolism are influenced over time.
Over the years acquired an affected immune system
And, in this case, it is smoking that stands out for its influence, rather than other factors such as sleep time or degree of physical activity, according to researchers led by biologist Violaine Saint-André.
This is not new at all. We know that smoking affects the “innate” immune system – which is common to everyone – by increasing inflammatory responses. Studies confirm this, finding that this effect disappears soon after smoking cessation. But, and this is the great innovation, it is not the same as acquired immunity. For some individuals, the effects persist for years, even decades, after smoking cessation, even though the sample is too small and the responses too variable to put forward a definite average duration.
The researchers went further by showing that these disturbances are associated with an “epigenetic” effect: people’s DNA remains the same, of course, but exposure to tobacco affects the way certain genes are expressed in practice. We should certainly not conclude from this that quitting smoking is useless. These effects eventually subside. But “to preserve your long-term immunity, it’s definitely better to never start smoking,” Ms. Saint-André insisted during a press conference.
Quitting is still worth it
The study, which is based on biological assays, however, cannot say what the health consequences of these immune differences are. According to the authors, there may be effects on the risk of infection, cancer or autoimmune diseases. But this is, at this stage, a hypothesis.
Another study, published last week, tries to determine the extent to which health risks actually remain after you’ve stopped smoking. Published in NEJM Evidence, it is based on data from about 1.5 million people in Canada, the United States, Norway and the United Kingdom.
The researchers compared mortality rates between several groups: active smokers, people who never smoked, and more or less long-term smokers. And, later, risks take time to fully resolve. Once you stop smoking, you have to wait ten years to regain life expectancy compared to a non-smoker.
But, here again, we must avoid the conclusion that stopping is not quickly worth it: “the benefit is already visible after three years”, the researchers note, with an average survival of five years in this group, which is half of the normal life expectancy. . And the effect is significant regardless of the age at which you stop, although it is more marked in people under 40.
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