A new international study has delivered a stark reminder that there is no “safe” level of smoking — not even a few cigarettes a day. Published in PLOS Medicine, the research shows that even low-intensity smoking sharply increases the risk of cardiovascular disease and early death.

The study, led by Dr. Erfan Tasdighi from the Johns Hopkins Ciccarone Center for Prevention of Cardiovascular Disease, analyzed data from more than 323,000 adults across 22 long-term studies. Participants were tracked for nearly two decades, giving researchers one of the most detailed pictures to date of how smoking habits affect long-term health.

The findings are alarming. Compared with people who never smoked, those who smoked just two to five cigarettes a day had significantly higher risks of serious heart conditions — including atrial fibrillation, heart failure, and cardiovascular disease deaths. Their risk of dying from any cause was also markedly higher.

For those smoking between 11 and 15 cigarettes daily, the danger spiked even further, with the risk of cardiovascular disease nearly doubling.

Researchers also noted that the steepest rise in damage happens early — during the first 20 pack-years and at around 20 cigarettes per day, reinforcing the idea that harm accumulates quickly.

But there was encouraging news as well. The study found that quitting smoking brings substantial benefits, especially in the first 10 years after stopping. Over time, former smokers continued to see their risks fall, and within 20 years of quitting, their risk of heart disease was 80 percent lower compared to people who continued to smoke.

Dr. Tasdighi and his team stress that the message could not be clearer. “It is remarkable how harmful smoking is — even low doses of smoking confer large cardiovascular risks,” the authors said. They emphasized that quitting early offers the greatest protection: “The time since complete cessation matters more than reducing daily cigarette quantity.”

The findings add to a growing body of evidence urging smokers — even occasional ones — to quit as soon as possible. For heart health, experts say, cutting down is not enough. Only quitting completely makes a meaningful difference.