"Smoking just a few cigarettes each day is just as bad for your lungs as burning through two packets," reports the Mail Online.
The headline reports a study that pooled the results of 6 population-based studies from the US including over 25,000 adults. It found that people's lung function – the amount of air that lungs can inhale and exhale – decreases almost as fast in people smoking 5 or fewer cigarettes a day, as people smoking 30 or more.
Lung function declines in most people as we get older. However, smoking has long been recognised as the main cause of chronic obstructive pulmonary disease (COPD), where there is inflammation and narrowing of the air passages. This makes people get short of breath easily and have persistent cough.
As expected, the study found that lung function declined faster for smokers compared with people who had never smoked. Lung function was poorer the more cigarettes people smoked, but even "light" smokers were not far behind heavy smokers.
They also found that lung function continued to decline in people who quit smoking, although not nearly as fast as those who continued to smoke.
The researchers say their study shows that "there is no safe level of tobacco smoke" and that people wanting to avoid lung disease should stop smoking completely.
The study focused only on lung function and did not consider the other established harms caused by smoking, such as cancers and heart disease.
Many people think that smoking occasionally or at a low level is almost as good as stopping completely. This study shows that's not the case. Find out more about how to stop smoking.
Where did the story come from?
The study was carried out by researchers in several universities in the US, led by Columbia University, the National Cancer Institute and the National Institute of Environmental Health Sciences. It was funded by the National Institutes for Health and published in the peer-reviewed journal The Lancet Respiratory Medicine.
While the Mail Online report was mostly accurate and balanced, the headline saying that light smoking was "just as bad" as heavy smoking is not strictly true. Light smoking resulted in lung function loss at 68% of the rate of heavy smoking.
What kind of research was this?
This was a cohort study pooling the results of 6 US cohorts that included measures of lung function and smoking status.
Researchers wanted to see how lung function decline differed among current smokers, former smokers and people who had never smoked.
Cohort studies are a good way to measure changes over time among big groups of people. While cohort studies alone cannot prove that a risk factor (such as smoking) causes a decline in lung function, we already have enough evidence from other studies to prove that.
What did the research involve?
Researchers used data from 6 cohort studies that had recruited people from 1983 to 2014. The studies covered different age ranges – 2 looked at young adults, 2 at middle-aged adults and 2 at older adults.
People had their lung function tested using a spirometer, which measures how much air people breathe out in the first second of forced expiration (forced expiratory volume, known as FEV1).
They took at least 2 tests, an average of 7 years apart. They reported whether they were a current, former or never smoker, and how much they smoked or had smoked in the past.
Researchers calculated the average annual rate of lung function decline at age 57.
They compared the rate in former, current and never smokers, and in people who smoked 5 or fewer and 30 or more cigarettes a day. They also looked at the effects of how much tobacco people had consumed overall, and how long since they had stopped smoking (for former smokers).
They adjusted their figures to take account of people's age, height, sex, ethnicity, bodyweight, birth year and education. They also took account of which individual cohort study people were from, and whether they had been diagnosed with lung disease.
What were the basic results?
The study included 25,352 people made up of:
- 10,087 who never smoked
- 6,989 former smokers
- 2,462 current smokers
- 5,814 people who changed smoking status between the 2 lung function measurements
The average annual rate of lung function decline at age 57 was:
- 31.01mL less for people who never smoked
- 34.97mL less for people who used to smoke
- 39.92mL less for people who currently smoke
After accounting for potential confounding factors, researchers found current smokers had a worsening in lung function 9.21mL a year faster than never smokers. Former smokers had a worsening in lung function 1.82mL a year faster than never smokers, so about 20% the amount of current smokers.
Looking at current smokers, they found:
- those smoking 5 cigarettes or fewer a day saw their lung function worsen by 7.65mL a year more than never smokers
- those smoking 30 cigarettes or more a day saw their lung function worsen by 11.24mL a year more than never smokers
The results were more pronounced in people who had been diagnosed with lung disease.
They also found that, among former smokers, the decline in lung function got less the longer it was since they had quit. People who had stopped smoking 30 years previously still had a slightly faster decline in lung function than those who had never smoked, but not as fast as those who had stopped more recently or who still smoked.
How did the researchers interpret the results?
The researchers said: "In conclusion, our findings show that former smokers and low-intensity current smokers have accelerated lung function decline compared with never-smokers."
They added: "Our results therefore reinforce the view that there is no safe level of tobacco smoke exposure and that smoking cessation is the most effective means of harm reduction."
These results add to the weight of evidence that shows that any level of tobacco smoking is harmful and that the best way to protect lung health – and health more generally – is to stop smoking altogether.
The study has some limitations to be aware of. People self-reported whether or not they smoked, and how much. This might not be completely accurate. However, if people reported not smoking when they did smoke, or smoking fewer cigarettes than they actually smoked, this could make the results less accurate.
Few people in the study (118 of 2,462 current smokers) said they smoked less than 5 cigarettes. This means the figure for lung function decline in this group may not be precise.
But despite these issues, the risks from smoking, not only in terms of COPD but a wide range of cancers, cardiovascular disease and many other chronic diseases, are well established and proven by evidence.
You may not be able to completely reverse and undo any health effects from smoking, but this study supports the known fact that the best way to limit lung damage, and other harmful effects from smoking, is to stop smoking altogether, and that the sooner you stop, the better.
The best way to stop smoking is with NHS Stop Smoking services. Find out how the NHS can support you to stop smoking.
Analysis by Bazian
Edited by NHS Website
Links to the headlines
The Mail Online, 10 October 2019
Links to the science
The Lancet. Published online 9 October 2019