Smoking leaves a mark for decades: scientists estimate the risk of heart death
Almost 30 years of observations have shown how the number of cigarettes smoked and the time after quitting smoking are associated with a long-term risk of sudden cardiac death. Scientists have found that the probability of such an outcome increases in both current and former smokers, but after quitting cigarettes, the risk gradually decreases. All the details are in the Izvestia article.
Almost three decades of observations
Researchers from Denmark and Japan examined data from the population-based Copenhagen Urban Heart Study. It began in 1976, and surveys of participants were conducted approximately once every 10 years. The new study included participants in the third survey, which took place in 1991-1994, after which they were monitored until death or December 2021. The smoking status was assessed on the third examination, and then again on the fourth, with the second assessment used in additional analyses.
A total of 10,038 people were included in the study, of which 9,106 participants were included in the main analysis. During the follow-up period, the median duration of which was 28.6 years, the scientists recorded 890 cases of sudden cardiac death. To assess the effects of smoking, the researchers took into account the fact of smoking itself, the number of years after quitting cigarettes among former smokers, and the cumulative effect expressed in pack-years.
The researchers also used models to assess the association between smoking and the risk of sudden cardiac death, taking into account other factors. The main analysis included gender, age, education, alcohol consumption, leisure-time physical activity, and income. The additional model also took into account diabetes, cardiovascular diseases, and chronic obstructive pulmonary disease.
In addition, the researchers assessed overall mortality, classified deaths into sudden cardiac, other cardiac and non-cardiac deaths, and analyzed the association of smoking with a number of metabolic and cardiovascular indicators. The results were published on the online portal News Medical.
Smoking was found to be associated with a higher risk
At the time of the start of the follow-up, former smokers were older than people who had never smoked, and more often had concomitant diseases. Current smokers had higher alcohol consumption, less physical activity in their free time, and lower socioeconomic status. Among former smokers, the median time after quitting smoking was 14.5 years, while current smokers had a median cumulative exposure of 26.2 pack-years.
Compared to people who had never smoked, both current and former smokers were associated with an increased risk of sudden cardiac death. The risk ratio was 1.88 for current smokers and 1.34 for former smokers. These results remained comparable even after additional adjustments for diabetes, cardiovascular disease, and chronic obstructive pulmonary disease.
The analysis of total mortality also showed differences between the groups. After 20 years, the rate was 25.5% among current smokers, 20.4% among former smokers, and 17.4% among people who had never smoked. The excess overall mortality compared to those who had never smoked was 8.2 percentage points for current smokers and 3 percentage points for former smokers. At the same time, sudden cardiac death accounted for between 13% and 16% of the total mortality in all smoking categories.
The longer the smoking experience, the higher the risk.
Researchers have found a correlation between the risk of sudden cardiac death and the cumulative effects of smoking. As the amount of smoke increased, the risk gradually increased, but at the highest levels of exposure, this relationship largely reached a plateau. In the category with accumulated exposure from 40 to 159 pack-years, the risk ratio was 2.50 compared to people who had never smoked.
The researchers also estimated what proportion of the excess total mortality was sudden cardiac death. Among current smokers, it accounted for 17.1% of excess mortality, and among former smokers — 26.8%. Thus, sudden cardiac death was one of the components of increased mortality associated with smoking.
Additional analysis showed differences in a number of health indicators. Current smokers had lower levels of creatinine, body mass index, systolic blood pressure, and high-density lipoprotein cholesterol, and their resting heart rate was higher than those who had never smoked. At the same time, total cholesterol did not differ significantly between the groups, and no significant differences were found in the studied indicators among former and never smokers.
After failure, the risk gradually decreases.
One of the key results was a reduction in the risk of sudden cardiac death as the time after quitting smoking increased. In former smokers, the probability of such an outcome gradually decreased with increasing duration of abstinence. People who had not smoked for the longest period — from 26 to 67 years — had a risk approaching the level of those who had never smoked.
At the same time, the risk remained elevated in the first decades after the failure. The authors of the study note that the data obtained indicate a gradual reduction in risk, rather than its instant return to the level of never-smokers after stopping using cigarettes.
The researchers emphasized that the work was observational and therefore does not allow establishing a cause-and-effect relationship. In addition, the participants provided information about smoking independently, the number of pack-years was assessed only at the initial stage, and smoking behavior was recorded only on two surveys.
Finally, the study was conducted among the urban population of Denmark, so its results may not fully apply to other population groups and current smoking patterns. The authors consider the results to be an additional argument in favor of smoking prevention and earlier smoking cessation to reduce the burden of sudden cardiac death.
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