A nationwide study has indicated that initiating smoking at an early age, particularly before 20 years old, is associated with a lasting impact on cardiovascular health, increasing the risk of heart attack, stroke, and early death in adulthood. This risk is present even when accounting for similar cumulative smoking exposure.
Study Objectives
Researchers investigated the independent association between the age at which individuals begin smoking and future risks of myocardial infarction (MI), combined cardiovascular events, all-cause mortality, and stroke. They also examined if early initiation modifies the effects of cumulative smoking exposure.
Methodology
The study utilized a retrospective cohort from a national health database in Korea, encompassing 9,295,979 adults over 20 years old. Participants had no prior history of stroke, MI, or end-stage kidney disease and had participated in a health screening program in 2009.
Smoking information, including age at initiation, current or former status, and cumulative exposure (pack-years), was self-reported. Baseline demographic, clinical, laboratory, and lifestyle data were collected as covariates. Participants were followed until incident MI, stroke, death, or the end of 2018. Cox proportional hazards models were used for statistical analysis.
Key Findings
- 40.1% of the study population had a history of smoking, with nearly one-quarter of smokers having started before age 20.
- All smoker groups demonstrated higher probabilities of cardiovascular events and mortality compared to nonsmokers over approximately nine years of follow-up.
- Individuals who started smoking early and accumulated heavy exposure (20 or more pack-years) showed the highest risks:
- More than double the risk of MI (Hazard Ratio [HR] 2.43).
- Significantly increased risk of stroke (HR 1.78).
- Combined stroke or MI risk (HR 2.00).
- Elevated all-cause mortality (HR 1.82).
- These risks were notably higher than those observed in smokers with similar pack-years who initiated smoking later.
- A clear dose-response relationship was observed, where earlier initiation was linked to progressively higher cardiovascular risk, even after adjusting for total pack-years. The harmful effects of greater smoking exposure were amplified when smoking began at younger ages.
Interpretation and Limitations
The study suggests heightened vulnerability during adolescence and early adulthood to the cardiovascular harms of smoking. Strengths included the large sample size, long follow-up, and detailed adjustment for confounders.
However, limitations included reliance on self-reported data, potential recall bias, lack of information on changes in smoking habits or duration of cessation, unmeasured confounders, and a cohort predominantly composed of males and individuals of Asian descent, which may affect generalizability.
Public Health Implications
These findings suggest that preventing young people from initiating smoking, especially before age 20, could substantially reduce cardiovascular disease and premature death at a population level.