A large new study from South Korea shows that starting smoking at a young age significantly raises the risk of heart attacks, strokes, and early death, even when accounting for total lifetime cigarette exposure. People who began smoking before age 20 had the highest risks, suggesting that adolescence may be a particularly vulnerable period for long-term cardiovascular harm.
The study analyzed over 9 million adults aged 20 and older who participated in a national health screening in 2009. None had a history of heart attack, stroke, or severe kidney disease at the start. Participants reported their smoking habits, including age at initiation, current status, and cumulative exposure measured in pack-years. Researchers also considered other factors like blood pressure, cholesterol, diabetes, physical activity, alcohol use, and socioeconomic status.
Over roughly nine years of follow-up, smokers consistently showed higher risks than non-smokers. Early starters with heavy smoking histories (20+ pack-years) had more than double the risk of heart attack (HR 2.43), higher risk of stroke (HR 1.78), combined stroke or heart attack (HR 2.00), and increased all-cause mortality (HR 1.82). Even smokers with similar pack-years who started later had lower risks, highlighting that early smoking amplifies the harm of cigarettes.
The study also found a clear dose-response relationship: the earlier someone starts, the higher their cardiovascular risk, independent of total smoking exposure. These trends held across men and women, people with different metabolic health, and various smoking intensity levels.
Although the research relied on self-reported data and primarily involved Asian men, its huge sample size and long follow-up make the findings compelling.
From a public health perspective, the study emphasizes that preventing young people from starting smoking—especially before age 20—could dramatically reduce heart disease, stroke, and premature death. This adds to existing evidence that adolescence is a critical window for preventing long-term health damage from smoking.
REFERENCE: Koh, J.H., Han, K., Kim, M., Cho, J.M., Jung, S., Lee, S., Kim, Y., Cho, S., Huh, H., Kim, S.G., Kang, E., Joo, K.W., Kim, D.K., Park, S. (2026). Early age at smoking initiation is associated with elevated cardiovascular disease and mortality risk in a nationwide population-based cohort. Scientific Reports, 16, 3063, https://www.nature.com/articles/s41598-025-88253-4
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