Despite the industry having long fought to conceal the dangers of smoking, tobacco is now known to kill more than eight million people globally a year, according to the World Health Organization. But the myriad ways the habit damages bodies are still coming to light.
The new study, published in the journal Nature, found that smoking alters the immune system, which protects bodies from infection, for far longer than previously thought.
It particularly highlighted changes to what is called adaptive immunity, which is built up over time as the body’s specialised cells remember how to fight back against foreign pathogens they have previously encountered.
The findings were based on analysing blood and other samples taken from 1,000 healthy people in France starting from more than a decade ago.
Smoking was found to have more influence on adaptive immunity than other factors such as amount of sleep or physical activity, the researchers said.
The study also confirmed previous research that has shown smoking’s effect on “innate immunity”, which is the body’s first line of defence against invading pathogens.
While innate immunity rebounded immediately after people stopped smoking, adaptive immunity remained affected for years, even decades after quitting, the study said.
The sample size was too small to give a precise timeline for how long these changes last. The researchers nevertheless emphasised that the effect does wear off – so the sooner people quit, the better.
Of course, it is still better “for long-term immunity to never start smoking”, lead study author Violaine Saint-Andre of France’s Pasteur Institute stressed.
The researchers could not say for sure what consequences these changes may have on health, but they hypothesised it could affect people’s risk of infections, cancer, or autoimmune diseases.
The sooner the better
Another study, published last week in the journal NEJM Evidence, aimed to determine how much quitting smoking was linked to a lower risk of disease and dying early.
It covered 1.5 million people across the United States, Canada, Norway and the United Kingdom, some of them active smokers, some who never started – and everyone in between.
In detail, the research suggests that people who quit smoking before the age of 40 “can expect to live almost as long as those who never smoked”. Regardless of the age at which you decide to stop smoking, it only takes a decade to regain a survival rate similar, or almost, to that of non-smokers.
In addition, the researchers point out that half of this benefit occurs within three years of quitting. These findings underline the importance of giving up the habit at any age, since cessation is believed to be linked to longer survival in all cases.
The experts report that quitting smoking mainly reduces the risk of death from cardiovascular disease and cancer. It also reduces the risk of death from respiratory disease, albeit to a lesser extent, likely “due to residual lung damage”, they pointed out.
“Many people think it’s too late to quit, especially in middle age. But these results counter that line of thought: it’s never too late, the impact is fast, and you can reduce risk across major diseases, meaning a longer and better quality of life,” professor Prabhat Jha from the University of Toronto concluded.