Scientists from the Johns Hopkins Medical Center have found that simply reducing the number of cigarettes smoked per day does little to lower the risk of cardiovascular disease — only complete smoking cessation provides significant health benefits. The study results were published in PLOS Medicine.

The research combined data from 22 long-term cohort studies involving 323,826 adults who were followed for nearly 20 years. During this time, more than 125,000 deaths and 54,000 cardiovascular events were recorded. The researchers analyzed smoking history, the number of cigarettes smoked per day, and the time elapsed after quitting, using Cox proportional hazards models.

The average age of participants was around 60; most were women. At the time of enrollment, 14% were current smokers, 49% had quit, and 36% had never used tobacco products.

The analysis accounted for demographic factors, body mass index, diabetes, coronary artery disease, and alcohol use.

The results showed that even a few cigarettes per day were associated with a significantly increased risk of cardiovascular disease.

“The level of risk for current and former smokers is determined by three factors: duration of smoking, number of cigarettes per day, and the time since quitting. However, only complete smoking cessation substantially reduces the likelihood of developing heart and vascular diseases,” said Michael Blaha, M.D., Director of Clinical Research at the Ciccarone Center for the Prevention of Cardiovascular Disease and the study’s lead author.