People who smoke socially are more than twice as likely to die of lung disease and more than eight times as likely to die of lung cancer than non-smokers, a study suggests.
The research, presented at the European Respiratory Society International Congress, shows that the risk of lung cancer death for "social smokers" - those who smoke fewer than 10 cigarettes per day - is not substantially lower than those who smoke more than 20 a day.
Researchers said their 17-year-long study suggests that cutting down, or combining fewer cigarettes with vaping, is no substitute for quitting.
The research was by Dr Pallavi Balte and Dr Elizabeth Oelsner, at Columbia University Irving Medical Centre in New York.
Dr Balte told the virtual conference: "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, for example in the USA the proportion of smokers smoking less than 10 cigarettes per day has increased from 16% to 27%.
"So we wanted to study the risks to social smokers compared to people who don't smoke and compared to heavier smokers."
The study included 18,730 people selected from a multi-ethnic sample of the general US population with an average age of 61.
Researchers followed the people for an average of 17 years, during which time 649 died of respiratory disease and 560 died of lung cancer.
Among non-smokers, the proportion of people who died from respiratory diseases was 1.8% and the proportion who died of lung cancer was 0.6%.
Among social smokers - people who smoked fewer than 10 cigarettes a day - around 3.3% died from respiratory diseases and 4.7% died from lung cancer.
For heavy smokers - people who smoked more than 20 a day - these proportions were 10.1% and 12.9%, respectively.
The researchers calculated the death rates from respiratory disease and lung cancer and compared these rates between non-smokers, social smokers and heavy smokers.
They took account of other factors that can influence death rates, such as age, sex, race, educational attainment and body weight.
The researchers found that social smokers were 2.5 times as likely to die of respiratory disease and 8.6 times as likely to die of lung cancer, compared with non-smokers.