In a study funded by the National Heart, Lung, and Blood Institute, new research from Johns Hopkins Medicine adds to existing evidence that smoking fewer cigarettes does not eliminate cardiovascular disease risk, and quitting entirely is the most effective strategy for improving health.
Cigarette smoking is the leading preventable cause of disease, death and disability in the United States. According to the Centers for Disease Control and Prevention, over 16 million Americans are living with a smoking-related disease, making cigarette smoking a major public health concern.
In an effort to further address this issue, researchers sought to demonstrate the relationships among smoking burden, intensity and cessation duration across multiple heart and vascular-related health conditions. These findings, published Nov. 18 in the journal PLOS Medicine, add important evidence underscoring the urgent need to encourage early smoking cessation.
"Previous research established that cigarette smoking increases cardiovascular disease risk, but the exact relationship between smoking intensity and health outcomes remained unclear, especially for light-intensity smoking," says Michael Blaha, M.D., M.P.H., director of clinical research for the Johns Hopkins Ciccarone Center for the Prevention of Cardiovascular Disease and the study's corresponding author.
Researchers used baseline variables from a standardized data set developed by the Cross-Cohort Collaboration-Tobacco Working Group, which combined data from 22 cohort studies involving 323,826 adults, following participants for up to 19.9 years and documenting more than 125,000 deaths and 54,000 cardiovascular events. Researchers then applied Cox proportional hazard models to assess associations among overall smoking history, cigarettes per day and years since cessation in relation to cardiovascular outcomes.
Of the more than 323,000 adults, with an average age of about 60, most participants were women (76%). Among them, 14% were current cigarette smokers, 36% had never smoked and 49% were former smokers of conventional cigarettes.
A multivariable model was adjusted for age, sex, race, ethnicity and education status. A second multivariable model was adjusted for nine harmonized covariates, including body mass index, diabetes, history of coronary heart disease at baseline and any alcohol use. The reference group for all analyses was individuals who had never smoked.
The results of this study present one of the largest and most detailed analyses to date of the effects of different smoking measures on cardiovascular, cause-specific and all-cause mortality outcomes. "This study shows that even low levels of smoking — for example, only a few cigarettes a day — carry substantial cardiovascular risks," says Blaha. Quitting completely — not just cutting back — provides the greatest health benefit."
Additionally, these research findings provide specific estimates showing how much risk former and current smokers face, especially those who smoke only a few cigarettes per day, with the use of three factors — how long someone has smoked, how many cigarettes they smoke per day and how long it has been since they quit — each related to the risk of heart disease and death.
"Our findings illustrate the complex relationship between how much someone has smoked over time and how long it has been since they quit," says Blaha. "These results, which highlight the strong predictive value of longer time since quitting, reinforce the critical need to educate the public and promote early smoking cessation as one of the most effective strategies to reduce the risk of this deadly disease."
The study was led by Erfan Tasdighi, M.D., who conducted the research while at Johns Hopkins Medicine and is now a resident at Rutgers New Jersey Medical School.
