A large veteran study indicates that measuring smoking duration rather than relying solely on pack years could identify more people at risk of lung cancer.
The relationship between tobacco use and lung cancer is well established, but recent research has highlighted a blind spot in how risk is identified. A US team analysed data from nearly one million veterans aged 50 to 80 and found that people who smoked intermittently over many years — often described as social smoking — may carry a persistent risk that standard screening measures miss.
This challenges the widespread assumption that intensity and duration contribute equally to risk and suggests longer-term, lower-intensity patterns deserve more attention.
The study compared the traditional pack years metric — calculated by multiplying packs per day by years smoked — with a simpler focus on tobacco smoking duration, meaning the total years a person smoked regardless of daily quantity.
Researchers report that duration-based assessment performed at least as well as pack years and in some cases detected additional people who later developed lung cancer. The findings raise questions about current screening thresholds and who is invited for preventive checks.
How the researchers approached risk assessment
To test screening methods, investigators used large-scale health records to estimate five-year lung cancer risk under different metrics. The analysis showed that relying on pack years tended to prioritize heavy daily smokers, while a duration-first approach identified individuals with long histories of lighter use. The team noted that the self-reported nature of packs-per-day can be unreliable over decades, whereas counting years of smoking is simpler and often more consistent. By flagging people who had smoked for roughly two decades, regardless of intensity, the study reduced the share of missed cancers compared with current eligibility rules.
Implications for screening programs
Current US screening guidance commonly excludes people who stopped smoking more than 15 years ago, even if they smoked for many years earlier. Under those rules, the investigators estimated a substantial fraction of cancers would not have been caught by screening. Using smoking duration as an alternative criterion lowered the proportion of missed cases, suggesting that policies emphasizing only recent heavy use may overlook slowly accumulating risk. The results indicate a need to rethink eligibility so screening better aligns with how lung cancer risk actually develops across different smoking patterns.
Why duration matters
Smoking duration captures cumulative exposure over time in a way that is less vulnerable to recall bias than daily cigarette counts. For example, someone who smoked a few cigarettes at social events across 20 years might register a low pack years score but still have a significant cumulative exposure. The study’s authors argue that risk can build gradually and persist well after quitting, so duration-based measures could be a practical tool to broaden the reach of screening without relying on precise historical smoking intensity data.
What this means for occasional smokers and public health
For people who consider themselves occasional or social smokers, the message is sobering: light, long-term use is not harmless. Public health advocates emphasize that stopping entirely provides the greatest benefit, though risk reduction is progressive and may take years to become substantial. Organisations monitoring tobacco harms have pointed out that many people who reduce consumption through vaping or cutting down still keep some cigarettes, and that partial reduction does not eliminate cancer risk. The study reinforces the need for high-quality cessation support for anyone attending lung health checks.
Policy and personal action
In the UK, for example, the NHS lung screening program offers checks to people aged 55 to 74 who have a history of smoking, and invitations are directed to those who have told their GP they currently smoke or smoked in the past. Experts say screening initiatives should be paired with robust quitting services so attendees receive help to stop completely. Ultimately, both clinicians and policymakers may need to consider simple, reliable measures such as smoking duration to ensure that the slow but real risks of social smoking are not underestimated.
