People with poor lung function are at an increased risk of developing lung cancer, suggests a study in Thorax.

Lung cancer is the most lethal cancer in the world, killing 328 million people globally in 2000. The leading cause of lung cancer is cigarette smoking.

Researchers analysed studies that examined the relationship between lung function (measured by forced expiratory volume in one second or FEV1) and lung cancer. To ensure the results were as accurate as possible, only large studies that adjusted for smoking habits were included.

The analysis included 204,990 participants, of whom 6,185 had or died from lung cancer. The average age of participants ranged from 42-47 years and follow up time was 9-18 years.

Compared with the best lung function measurements, men with the worst lung function had more than twice the risk of lung cancer, and women had nearly four times the risk.

Even relatively small reductions in lung function, which are considered within the normal range, increased the risk of lung cancer by 30-60%, especially among women. Other smaller studies, not included in this analysis, showed similar results.

Independent of cigarette smoking history, reduced FEV1 increases the risk for lung cancer in the general population, say the authors.

Possible explanations for this relationship include lung and airway inflammation caused by cigarette smoke and other noxious irritants. Alternatively, individuals who have reduced FEV1 may have an impaired ability to clear inhaled carcinogens from their airways.

Despite some limitations, the authors believe that these findings are a step forward in helping doctors to uncover the disease at an earlier stage. Furthermore, since lung cancer can occur in individuals with only small decreases in FEV1 (especially in women), the traditional boundaries of "normal" FEV1 may need to be modified for screening purposes, they conclude.

Relationship between reduced forced expiratory volume in one second and the risk of lung cancer: a systematic review and meta-analysis Thorax 2005; 60: 570-75

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