Only complete smoking cessation saves the heart, scientists have confirmed

Smoking remains the leading preventable cause of disease, disability and death. The authors of a paper published in the journal PLOS Medicine decided to evaluate in detail how total "tobacco years", smoking intensity and duration of cessation are associated with the risk of nine cardiovascular outcomes and mortality.

One of the largest studies on smoking and the heart

The researchers used a standardised Cross-Cohort Collaboration-Tobacco Working Group dataset that combined information from 22 cohort studies and a total of 323,826 adults. Participants were followed for up to 19.9 years, during which period there were more than 125,000 deaths and 54,000 cardiovascular events.

The association between smoking and risk was assessed using Cox proportional hazards models. Three key parameters were taken into account:

• total years of smoking,

• number of cigarettes per day,

• how much time had elapsed since quitting.

The average age of the participants was around 60 years. Among them:

• 14% were current smokers,

• 36% had never smoked,

• 49% were former smokers.

The reference group in all analyses was people who had never smoked.

Models were adjusted for age, sex, race, ethnicity, and education level, and then adjusted for nine additional factors (body mass index, diabetes, history of coronary heart disease, alcohol use, etc.).

Even "a couple of cigarettes" is a significant risk

According to lead author Professor Michael Blaha, director of clinical research at the Ciccarone Centre for Cardiovascular Disease Prevention, the work provides one of the most detailed insights to date into how different smoking parameters are associated with cardiovascular events and mortality.

"This study shows that even low levels of smoking - just a few cigarettes a day - carry significant cardiovascular risk. The greatest effect comes from complete smoking cessation, not just reducing the number of cigarettes," Blach emphasises.

The authors obtained specific risk estimates for current and former smokers, including those who smoke little. Both duration of smoking, number of cigarettes per day, and time since quitting were shown to increase or decrease the likelihood of cardiovascular disease and death in their own ways.

"Our results demonstrate the complex nature of the association between how much a person smoked during their lifetime and how long ago they quit," Blach notes. It was the longer time since quitting that showed particularly high predictive value: the earlier one quits, the more time the body has to reduce risk.

The main message: quit completely and as early as possible

The researchers conclude that public health must do more to encourage early and complete smoking cessation, rather than creating the illusion of safety through "moderate" or "occasional" smoking.

Project leader Erfan Tasdighi (at Johns Hopkins Medicine at the time of the study, now a resident at Rutgers New Jersey Medical School) and his colleagues emphasise that the key conclusion of the study is simple - "smoking less" is clearly better than "smoking a lot", but only complete cessation and a sufficiently long period without tobacco can provide real protection for the heart and blood vessels.