Among the 45 million smokers in the United States, about 19 percent don’t smoke every day. These occasional smokers — people who smoke only on the weekends or just a few times a week in social situations — often believe they are avoiding the health worries typically associated with smoking.

But new research shows that even occasional cigarette smoking can impair artery function, a sign of looming heart disease.

In a small study, researchers at the University of Georgia recruited 18 healthy college students, half of whom were nonsmokers. The other half were occasional smokers, who puffed less than a pack a week and had not smoked for at least two days before undergoing testing. The study, published online in the journal Ultrasound in Medicine and Biology, used ultrasound scans to measure how the students’ arteries responded to changes in blood flow.

The researchers used a blood pressure cuff to reduce blood flow to the forearm for up to 10 minutes. Then they rapidly deflated the cuff and measured how the main artery in the forearm responded to the sudden change in blood flow.

The study found that the arteries of occasional smokers were 36 percent less responsive to changes in blood flow than nonsmokers. After the initial test, the occasional smokers had two cigarettes before undergoing the test again. That exam showed that arterial responsiveness dropped by another 24 percent compared to before they smoked.

“We wanted to determine whether occasional smoking can impair flow-mediated dilation and found that repeated bouts of cigarette smoking — even if classified as occasional — appear to increase the risk for developing cardiovascular disease in otherwise healthy, young people,” said lead author Lee Stoner, a former doctoral student and now a researcher at Christchurch Hospital in New Zealand, in a press release.

The researchers said the lasting effect of occasional smoking on artery health was surprising.

“Most people know that if they have a cigarette or two over the weekend that it’s not good for their arteries,” said study co-author Kevin McCully, a professor of kinesiology in the University of Georgia College of Education, also in a press release. “But what they may not be aware of is that the decrease in function persists into the next week, if not longer.”