Adults who smoked between one and 10 cigarettes per day had 1.5 times the risk of dying from cardiovascular disease compared to those who never smoked, according to a prospective cohort study.

Smokers also had more than six times the risk of dying from respiratory diseases such as emphysema.

Lead researcher Maki Inoue-Choi, PhD, MS, of the National Cancer Institute and National Institutes of Health in Rockville, Maryland, and colleagues published their results online Dec. 5 in JAMA Internal Medicine.

“The results of this study support health warnings that there is no safe level of exposure to tobacco smoke,” Inoue-Choi said in a news release. “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 evaluated data on 290,215 adults who participated in the National Institutes of Health-AARP Diet and Health Study and filled out a questionnaire on their cigarette smoking history during nine periods of their lives. The participants were 59 to 82 years old in 2004 and 2005.

The mean age of participants was 71 years old, while 57.9 percent were men, 7.7 percent were current smokers, 53.9 percent were former smokers and 38.4 percent never smoked.

Of the current smokers, 6.8 percent said they smoked fewer than one cigarette per day, and 30.4 percent said they smoked one to 10 cigarettes per day. Most of those participants said they smoked more cigarettes earlier in their lives.

The researchers found that participants who even smoked fewer than one cigarette per day had an increased risk of all-cause mortality. In addition, former consistent smokers of one to 10 cigarettes per day who quit smoking had higher all-cause mortality and mortality from cancer, lung cancer and respiratory disease compared with never smokers.

Further, former smokers who smoked between one and 10 cigarettes per day and quit at an older age had a higher all-cause mortality risk compared with those who quit at a younger age.

Adults who smoked less than one cigarette per day on a regular basis had a 64 percent higher risk of earlier death, while those who smoked between one and 10 cigarettes per day had an 87 percent higher risk of earlier death compared with people who never smoked.

The researchers cited a few limitations of the study, including that there was a modest number of low-intensity smokers. They also mentioned that participants recalled their smoking retrospectively, which could have led to recall bias. Further, most participants were white and in their 60s and 70s, so the results might not be generalizable to other groups.

“These findings provide further evidence that there is no safe level of cigarette smoking,” the researchers wrote. “All smokers should be targeted for smoking cessation, regardless of how few cigarettes they smoke per day. Further studies are needed to examine the health risks of low-intensity cigarette smoking in combination with electronic nicotine delivery systems and other tobacco products.”