When you stop smoking, the counters take a long time to return to zero. Two recent studies demonstrate the lasting effects of smoking on health. Our immunity, in particular, seems even more damaged than expected. “Smoking modifies adaptive immunity in a persistent manner,” concludes a study published this Wednesday in the journal Nature.
One element highlighted: adaptive immunity
This work marks an important advance in understanding the deleterious health effects of smoking which, according to the World Health Organization (WHO), kills some eight million people per year worldwide. It highlights an element hitherto ignored: adaptive immunity, which is built over time with infections, remains damaged for years after stopping smoking.
These conclusions are based on a sample of 1,000 people. These were selected more than ten years ago, as part of a project led by the Pasteur Institute in Paris, and their immunity was then regularly studied via various tests, particularly blood tests.
This type of project, called a cohort project, is very robust for assessing how different factors influence health and metabolism over time. And, in this case, it is smoking which stands out for its influence, more than other factors such as sleep time or the degree of physical activity, according to researchers led by biologist Violaine Saint-André.
This is not entirely new. We knew that smoking affects “innate” immunity – that which is common to everyone – by aggravating inflammatory responses. The study confirms this, finding that this effect disappears immediately after stopping smoking. But, and this is the great novelty, it is not the same thing for acquired immunity. This remains, for certain individuals, affected for years, even decades, after stopping smoking even if the sample is too small and the reactions too variable to put forward a precise average duration.
Effects that resolve
The researchers went further by showing that these disturbances are linked to an “epigenetic” effect: people’s DNA of course remains the same but exposure to tobacco affects the way in which 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 is surely better never to start smoking,” Ms. Saint-André emphasized during a press conference. This study, which is based on biological examinations, cannot however say what the consequences of these immune variations are for health. According to the authors, there could be effects on the risk of infections, cancers or autoimmune diseases. But this is, at this stage, a hypothesis.
Another study, published the previous week, attempts to determine to what extent the health risks really persist when you have stopped smoking. Published in NEJM Evidence, it is based on data concerning some 1.5 million people in Canada, the United States, Norway and the United Kingdom.
The researchers compared mortality between several groups: active smokers, people who have never smoked, and more or less long-term smokers. And, for the latter, the risks take time to fully resolve. Once you have stopped smoking, you have to wait ten years to regain a life expectancy comparable to someone who has not smoked at all.
But, here again, we must avoid concluding that stopping is not quickly worth it: “benefits already appear three years later”, note the researchers, with five years of survival regained on average in this group This is half the way to normal life expectancy. And the effect is notable regardless of the age at which you stop, even if it is more marked among those under 40.