Current Smokers at Higher Risk of IPF Than Former Smokers
Smoking cigarettes substantially increases the risk of developing idiopathic pulmonary fibrosis (IPF), according to a population-based study conducted in Korea.
The findings indicate the risk of IPF is greater in current smokers, compared with people who used to smoke but have since quit.
The study, “Impact of smoking on the development of idiopathic pulmonary fibrosis: results from a nationwide population-based cohort study,” was published in the journal Thorax.
Although the exact cause of IPF is unknown, certain factors are known to increase a person’s risk of developing the condition. Smoking cigarettes is perhaps the most well-established risk factor for IPF. A wealth of studies have demonstrated that cigarette smoke can cause lung damage that sets the stage for fibrosis (scarring).
Despite this well-established biological link, some aspects of the relationship between smoking and IPF are not fully understood. In particular, it is not yet clear how being a former smoker affects the risk of developing IPF, relative to never-smokers or current smokers.
To gain insight into these relationships, a team of scientists in South Korea conducted an analysis of data from the National Health Insurance Service (NHIS), the governmental program that covers virtually all people living there.
The team identified more than 23.2 million Koreans who underwent routine check-ups between 2009 and 2012. Approximately half (50.7%) were male, with a mean age of 47.7 years. At the time of the initial check-up, none of these individuals had been diagnosed with IPF. Based on self-reported questionnaires, 24.6% of the individuals analyzed were current smokers, 13.5% were former smokers, and 61.9% were never-smokers.
By the end of 2016, 25,113 (0.11%) of the people analyzed had been diagnosed with IPF. In this group, 27.2% of patients were current smokers, 23.2% were former smokers, and 49.6% were never-smokers. Also of note, 68.9% of individuals in the IPF group were men, which was in line with the known increased risk of IPF in males.
Using statistical models, researchers compared the risk of developing IPF in current smokers, former smokers, and never-smokers. These mathematical models took into account factors such as age, sex, alcohol consumption, physical activity, and income.
Results showed that, compared to never-smokers, current smokers were 66% more likely to develop IPF. The risk of IPF also was significantly higher in former smokers, who were approximately 42% more likely to develop the condition than never-smokers.
Further analyses compared current and former smokers. Results showed that current smokers were 17% more likely to develop IPF than former smokers.
Sex-stratified analyses indicated the extent to which smoking increased IPF risk was larger in women than men. However, researchers noted a need for caution in interpreting these results, stressing that this analysis was limited by the comparatively small number of female patients.
Additional analyses also indicated the risk of IPF correlated with cigarette consumption. In other words, people who smoked more heavily, and/or for a longer period of time, were statistically more likely to develop IPF. This association was particularly strong among men.
Researchers noted their study had several limitations, including the fact that it relied on insurance data, and that it was conducted in a single country with one dominant ethnicity, so results may not be reflective of all people.
Nevertheless, “this nationwide population-based cohort study demonstrated that smoking significantly increased the risk of IPF development,” the researchers wrote.