Social smokers damage their lungs just as much as those who go through multiple packs a day, new research has suggested.
US researchers found current lung cancer screening guidelines miss nearly half of all cases, by focusing on heavy smokers and overlooking those who smoke occasionally over many years.
The risk of developing the disease may persist for decades after quitting, researchers said, raising concerns that people who only smoked occasionally in their younger years could still face long-term health risks.
At present, in the US, guidelines typically use pack years to assess a person’s lung cancer risk.
This is calculated by multiplying the number of cigarette packs smoked per day by the number of years a person has smoked.
This is based on the assumption that both smoking intensity and duration are equally important when it comes to lung cancer risk.
However, experts now say this may not be the case and even smoking infrequently over an extended period of time – a phenomenon dubbed ‘social smoking’ – can pose serious health risks.
Smoking cigarettes is the single biggest risk factor for lung cancer. There are now around 50,200 new cases diagnosed each year in the UK and it is the leading cause of cancer deaths worldwide.
Even socially smoking can take years off your life, research suggests
The study – which will be presented at the annual meeting of the American Society of Clinical Oncology (ASCO) later this month – analysed data from nearly one million veterans aged 50 to 80-years-old.
The researchers compared how a person’s risk of developing lung cancer in the next five years changed based on whether they used the standard pack years metric or focused more simply on years smoked.
They found that measuring how many years someone had smoked for – referred to as tobacco smoking duration – performed at least as well as standard pack-year calculations and, in some cases, flagged more people at risk.
Crucially, relying on existing screening criteria meant a significant number of cancers would have been missed.
As it stands, in the US, people who haven’t smoked for 15 years or more are not usually eligible for screening – regardless of how long they smoked for when they were younger.
Under these guidelines, roughly one in six cases fell outside screening eligibility.
But when researchers used smoking duration alone – flagging people who had smoked for around 20 years for example, regardless of how heavily – the proportion of missed cancers dropped to just 7.5 per cent.
They concluded the findings suggest current guidelines may fail to accurately flag those whose risk builds slowly over time, rather than daily heavy smoking.
Experts have long known that stopping smoking at any age helps to reduce the risk of cancer, with the most substantial drops in cancer risk coming after the first decade of stubbing out – but risk does not disappear entirely.
The new study adds to evidence that risk may remain elevated for much longer than current screening cut-offs in some countries account for.
Hazel Cheeseman, chief executive at Action on Smoking and Health, said: ‘This study adds to the growing evidence that even occasional smoking carries serious health risks, including an increased risk of cancer.
‘That is particularly concerning in England, where we are seeing a rise in the number of people who smoke occasionally rather than every day.
‘Many smokers are cutting down by using vapes, but are not switching completely.
‘People need to understand that reducing the number of cigarettes they smoke without stopping entirely still poses a substantial risk to health.’
The team added that smoking duration is also easier to measure more reliably than pack years, which depends on people accurately recalling how much they smoked per day over decade.
For social smokers, the message remains clear: even smoking little and often can increase the very real risk of lung cancer.
In the UK, anyone aged between 55 and 74 who has ever smoked may be given the opportunity to take part in lung cancer screening, according to the NHS.
The screening initiative, which began in 2019, is still being rolled out across England, with areas with higher lung cancer rates prioritised.
Crucially, only those who have informed their GP that they currently smoke or have smoked in the past will be invited.
Action on Smoking and Health added that all smokers who attend a lung health check should be offered access to high-quality support to help them quit.
