Social smokers are at least eight times more likely to die of lung cancer and more than twice as likely to die of lung disease, compared to non-smokers, a new study has found.

According to US researchers, "smoking is dangerous regardless of whether you are a heavy smoker or a social smoker, so if you don't want to die of lung cancer, the best action is to quit completely".

The study involved over 18,700 adults, who were followed for an average of 17 years. During this time, over 1,200 died of lung disease or lung cancer.

"Everyone knows that smoking is bad for you, but it's easy to assume that if you only smoke a little, the risks won't be too high.

"Previous research suggests that people are cutting down on smoking. We wanted to study the risks to social smokers compared to people who don't smoke and compared to heavier smokers," commented Dr Pallavi Balte of the Columbia University Irving Medical Center in New York.

Social smokers were considered those who smoked less than 10 cigarettes per day.

The researchers calculated the death rates from lung disease and lung cancer and compared these rates between non-smokers, social smokers and heavy smokers. They also took into account other factors that can influence death rates, such as age, gender, education and body weight.

The study found that that social smokers were 2.5 times more likely to die of lung disease and 8.6 times more likely to die of lung cancer, compared to non-smokers.

When compared with heavy smokers, social smokers had around half the rate of death from lung disease, but their rate of death from lung cancer was two-thirds that of heavy smokers.

In other words, the risk of death from lung cancer is not substantially lower among those who smoke less than 10 cigarettes per day, compared to those who smoke more than 20 cigarettes per day.

"You might think that if you only smoke a few cigarettes a day, you are avoiding most of the risk. But our findings suggest that social smoking is disproportionately harmful," Dr Balte said.

Commenting on the findings, Prof Jørgen Vestbo, who is chair of the European Respiratory Advocacy Council, said that while the proportion of people who smoke habitually is falling in many countries, "we should still be concerned about those who identify as social smokers".

"This large study is important because it shows that smoking less will probably not have the effect that people are hoping for. We need to do all we can to support smokers to quit completely using evidence-based means, for example, with access to support services and nicotine patches or gum," he said.

Details of these findings were presented at the European Respiratory Society International Congress 2020, which is being held virtually this year.