A large US study by Oxford University found that smokers, especially those who started young, faced nearly three times the risk of dying prematurely from cardiovascular disease, but quitting smoking by age 40 may reduce that risk by 90%, reports the American Heart Association.
Risk was higher among smokers who began before age 15 compared to those who began at older ages – and highest of all for those who began smoking before age 10, according to the Journal of the American Heart Association article published on 28 October 2020.
Current smokers faced nearly three times the risk of premature death from cardiovascular disease compared with people who never smoked, the study found.
Smoking continues to cause an estimated 100,000 deaths from cardiovascular disease every year in the United States. Currently, there are about 25 million people who smoke daily including five million who became regular smokers before the age of 15.
Earlier research in Cuba found a correlation between childhood smoking and a higher risk for premature death overall. In this new study, investigators set out to determine if the findings were generalisable in other populations by conducting a similar analysis of US data focused on death from cardiovascular disease.
“It was surprising to see how consistent these findings were with our earlier research and with other studies from around the world, including from the United Kingdom, Australia and Japan, among others, both in terms of the substantial risks associated with smoking and with the health benefits of quitting smoking,” said lead study author Dr Blake Thomson, an epidemiologist at the University of Oxford in England.
“The age at which a person begins smoking is an important and often overlooked factor, and those who start smoking at a young age are at especially high risk of dying prematurely from cardiovascular disease.
“However, quitting can substantially reduce that risk, especially for those who quit at younger ages. Getting people to quit smoking remains one of the greatest health priorities globally.”
Using data collected between 1997 and 2014, from the annual US National Health Interview Survey, researchers examined the medical histories, lifestyle habits and demographics of smokers and non-smokers.
The study included 390,929 adults, ages 25 to 74 years (average age of 47), 56% female. Occasional smokers were excluded from the study. Current smokers were grouped by the age at which they began smoking.
During the follow-up period, 4,479 people died before the age of 75 from heart disease or stroke. After adjusting for potential confounding variables, such as age, education, alcohol consumption, region and race, researchers found:
- 58% were never smokers; 23% were ex-smokers; and 19% were current smokers.
- Among current smokers, 2% had started smoking before age 10, and 19% began smoking between ages 10 and 14.
- Those who quit smoking by the age of 40 reduced their excess risk of premature death from cardiovascular disease by about 90%.
Quitting smoking at any age offered benefits, and the earlier a person quit, the better, according to the findings. The analysis found that when compared to peers who had never smoked:
- Smokers who quit between ages 15 to 34 had about the same risk of dying from heart disease or stroke.
- Those who quit between ages 35 to 44 had about a 20% higher risk.
- Those who quit between ages 45 to 54 had about a 60% higher risk.
- Those who quit between ages 55 to 64 had about a 70% higher risk of death from heart disease or stroke.
- Those who were current smokers had nearly three times the risk of dying prematurely from heart disease or stroke.
“Preventing the next generation from smoking can save lives, but we must also emphasise that quitting smoking can save lives now, and in the years to come,” said Thomson. “Simply put, health policies should aim to prevent young people from smoking and should clearly communicate the benefits of quitting to those who do smoke, ideally as young as possible, and before the onset of serious illness.”
Stopping smoking is the priority
“This study adds to the body of evidence that starting to smoke at younger ages can significantly increase the risk of death from cardiovascular disease,” said Dr Rose Marie Robertson, deputy chief science and medical officer of the Association.
“It validates the American Heart Association’s position that smoking is a serious health hazard, that effective multi-episode counselling and medical therapies for cessation should be available to all, and that stopping smoking should be an urgent priority for smokers of all ages, especially the young.
“This data precedes the explosion in e-cigarette use in the US, and similar long-term outcomes from vaping can only be assessed over time. However, health risks have begun to emerge, and we know that vaping among teens is a precursor to smoking combustible cigarettes for many,” said Robertson, who is also co-director of the Association’s Tobacco Center of Regulatory Science.
Oxford’s Blake Thomson said more research is needed to better clarify the mechanisms by which prolonged smoking from childhood affects cardiovascular risk. Future research should also further examine the association between early smoking initiation and death from other causes, such as respiratory diseases and cancers, and in other populations.
Co-authors are Jonathan Emberson, Ben Lacey, Richard Peto, Mark Woodward and Sarah Lewington. Author disclosures are in the manuscript. The researchers reported no direct funding for this study.
Childhood Smoking, Adult Cessation, and Cardiovascular Mortality: Prospective Study of 390 000 US Adults
Journal of the American Heart Association. Published on 28 October 2020.
Blake Thomson, Jonathan Emberson, Ben Lacey, Richard Peto, Mark Woodward and Sarah Lewington
Author affiliations: The University of Oxford’s George Institute for Global Health, and Nuffield Department of Population Health.
Smoking still causes about 100,000 US deaths per year from cardiovascular disease. There were an estimated 25 million daily smokers in the United States in 2018, including 5 million who began smoking regularly in childhood (defined here as before age 15 years); of these, an estimated 0.5 million began before age 10 years.
Previous research has shown that, among daily smokers, those who began youngest have the greatest relative increase in overall adult mortality, but better evidence is needed on the relevance of the age when smoking began to cardiovascular adult mortality.
We investigated this using the annual US National Health Interview Surveys (a cross‐sectional household interview survey of the noninstitutionalized US population) linked to the National Death Index. Further details about the National Health Interview Surveys, and the anonymized data that support the findings of this study, are publicly available online here: https://www.cdc.gov/nchs/nhis/data‐questionnaires‐documentation.htm).
In 1997 to 2014, 424,793 US adults aged 25 to 74 years were surveyed and have been followed for mortality to 31 December 2015. Participants were asked about their health, habits (including smoking, drinking, and physical activity), medical history, and demographic details.
Current smokers were categorised by the age they began smoking regularly (as reported at recruitment): <10, 10 to 14, 15 to 17, 18 to 20, or >20 years. Occasional smokers were excluded. Ex‐smokers were categorised by the age they last smoked regularly: 15 to 34, 35 to 44, 45 to 54, or 55 to 64 years (excluding the few who had quit at older ages). Ex‐smokers who quit within 5 years of death were excluded to reduce reverse causality (by which smokers quit because of the onset of serious illness).
Causes of death were recorded according to the International Classification of Diseases, Tenth Revision (ICD‐10); our analyses of cardiovascular mortality included cardiac (I00–I09, I11, I13, I20–I51) and cerebrovascular (I60–I69) causes. Prospective analyses were restricted to “premature” deaths (here defined as ages 25–74 years).
Cox regression was used to estimate mortality rate ratios (RRs) comparing different smoking histories. For each baseline‐defined smoking group (including the reference group with RR = 1.0), the RR is shown with a group‐specific 95% CI that reflects the variance of the log risk in just that 1 group.
(The variance of the log RR comparing 2 different groups is the sum of the variance of the log risk in 1 group and the variance of the log risk in the other group.) The RRs were adjusted for age‐at‐risk (in 5‐year groups; 10 categories), sex, race (5 categories), education (4 categories), region (4 categories), and alcohol consumption (5 categories). All participants provided informed consent. Ethics approval for analyses of this publicly available anonymised dataset was not needed. Analyses used SAS v.9.4 and R v.3.1.1.
After excluding participants with missing information on smoking, covariates of interest, or mortality linkage, there were 390 929 participants aged 25 to 74 years (mean age 47, 56% female) at recruitment: 228 165 (58%) never smokers, 88 717 (23%) ex‐smokers, and 74 047 (19%) current smokers. Among current smokers, 1403 (2%) had begun before age 10 and 14 421 (19%) at ages 10 to 14 years.
During 3.5 million person‐years of follow‐up, 4479 died of cardiovascular disease before age 75: 1579 never smokers, 1227 ex‐smokers, and 1673 current smokers. For current smokers, the adjusted cardiovascular mortality RRs associated with starting to smoke regularly at ages <10, 10 to 14, 15 to 17, 18 to 20, and >20 years were 4.89 (95% CI, 3.90–6.12), 2.98 (2.68–3.31), 2.87 (2.64–3.13), 2.66 (2.41–2.94), and 2.45 (2.18–2.75), respectively, as against 1.00 (0.95–1.06) in never smokers.
Comparing current smokers who began in childhood (age <15 years) versus later (age ≥15 years), the RRs were 3.20 (2.90–3.52) and 2.69 (2.54–2.85), respectively, compared with never smokers (1.00; 0.95–1.06). For ex‐smokers, the RRs associated with smoking cessation at ages 15 to 34, 35 to 44, 45 to 54, or 55 to 64 years were 0.91 (0.81–1.02), 1.19 (1.06–1.33), 1.58 (1.42–1.76), and 1.69 (1.47–1.93), as against 2.80 (2.66–2.95) in current smokers and 1.00 (0.95–1.06) in never‐smokers.
Overall, current smokers in this contemporary US population had nearly 3 times the risk of premature cardiovascular mortality compared with never smokers. The risk was higher among those who had begun smoking in childhood (<15 years), and highest of all for those who had begun before age 10 years.
However, quitting at any age was associated with a substantially lower risk than continuing to smoke, with the greatest risk reduction among those who quit before age 40 years.
Age at starting to smoke is an important, but underappreciated, determinant of adult cardiovascular mortality, and this study indicates that the ≈5 million US smokers who began before age 15 years are at especially high risk of premature death from cardiovascular disease if they do not quit.
If the associations between smoking and cardiovascular mortality are largely causal, then smoking is a cause of more than two thirds of all premature deaths from cardiovascular disease among smokers who began before age 15 years.
However, smoking cessation substantially reduced the excess risk of cardiovascular death, with those who quit before age 40 years (preferably well before age 40 years) avoiding >90% of the excess cardiovascular risk, as well as avoiding substantial excess risks of death from other tobacco‐associated diseases.
Smokers, especially those who begin young, are three times more likely to die prematurely
Childhood Smoking, Adult Cessation, and Cardiovascular Mortality: Prospective Study of 390,000 US Adults