Even one cigarette a day is deadly, study finds

Less than one cigarette a day still drives up risk of early death by 64 per cent. Photo / Getty Images

Even occasional smoking - as little as half a cigarette a day - can be deadly, health officials warn in a new government study.

People who restrict themselves to fewer than seven smokes a week still have a 64 percent higher risk of an early death than non-smokers.

That figure is not far off the risk for heavy smokers, who are 87 per cent more likely to develop a life-threatening disease.

But researchers at the National Institutes of Health warn more and more people claim to smoke fewer than 10 a day, in the belief that it is healthier.

"The results of this study support health warnings that there is no safe level of exposure to tobacco smoke,' said lead investigator Maki Inoue-Choi.

"Together, these findings indicate that smoking even a small number of cigarettes per day has substantial negative health effects and provide further evidence that smoking cessation benefits all smokers, regardless of how few cigarettes they smoke."

The researchers looked at risk of death from respiratory disease, such as emphysema, as well as the risk of death from cardiovascular disease.

People who smoked between one and 10 cigarettes a day had over six times the risk of dying from respiratory diseases than never smokers and about one and half times the risk of dying of cardiovascular disease than never smokers.

Smoking has many harmful effects on health, which have been detailed in numerous studies since the US Surgeon General's 1964 report linking smoking to lung cancer.

The health effects of consistent low-intensity smoking, however, have not been well studied and many smokers believe that low-intensity smoking does not affect their health.

To better understand the effects of low-intensity smoking on mortality from all causes and for specific causes of death, the scientists analysed data on over 290,000 adults in the NIH-AARP Diet and Health Study.

Low-intensity smoking was defined as 10 or fewer cigarettes per day.

All participants were age 59 to age 82 at the start of the study.

Participants were asked about their smoking behaviors during nine periods across their lives, beginning with before they reached their 15th birthday until after they reached the age of 70 (for the older participants).

Among current smokers, 159 reported smoking less than one cigarette per day consistently throughout the years that they smoked; nearly 1500 reported smoking between one and 10 cigarettes per day.

The study relied on people recalling their smoking history over many decades, which introduced a degree of uncertainty into the findings.

Despite the large number of people surveyed, the number of consistent low-intensity smokers was relatively small.

Another limitation of the study is that the participants were mostly white and in their 60s and 70s, so the smoking patterns collected in the study reflect only a particular set of age groups in the United States.

Future studies among younger populations and other racial and ethnic groups are needed, particularly as low-intensity smoking has historically been more common among racial and ethnic minorities in the US.

The study also lacked detailed information about usage patterns among participants who reported smoking less than one cigarette per day.

Therefore, the researchers could not compare the effects of smoking every other day, every few days, or weekly, for example.