Smoking is a major risk factor for stroke in China, accounting for about one in seven strokes in men, researchers reported in Stroke: Journal of the American Heart Association.
"This study shows that smoking prevention and cessation could be an important approach to reducing the societal burden of stroke," said Jiang He, M.D., Ph.D., senior author of the study.
Many studies in western populations have shown that cigarette smoking is a strong and independent risk factor for stroke. But the relationship between cigarette smoking and stroke hasn't been well-studied in Asian populations -- including China, where stroke is the second leading cause of death.
"The study findings were consistent with reports from other populations, but in China this risk creates a huge public health problem," said He, the Joseph S. Copes Chair and professor of epidemiology at Tulane University School of Public Health and Tropical Medicine in New Orleans, La. "In addition to being the world's most populous nation, China is the world's leading producer and consumer of cigarettes."
Researchers from Tulane and the Chinese Academy of Medical Sciences in Beijing studied a representative sample of 83,533 men and 86,336 women, 40 years and older, from 17 provinces in mainland China. The participants were part of the third China National Hypertension Survey.
Researchers collected information on cigarette smoking and other health data when the study began in 1991. At that time, 59.1 percent of men and 13 percent of women reported being current smokers. The researchers followed participants for an average 8.3 years, during which time 6,780 strokes occurred, 3,979 of them fatal. After adjusting for other stroke-related factors, such as age and blood pressure, cigarette smoking was found to be a significant predictor of stroke.
Cigarette smoking accounted for 14.2 percent of strokes and 7.1 percent of stroke fatalities in men, and 3.1 percent of strokes and 2.4 percent of stroke deaths in women.
The longer and heavier a person's smoking habit, the higher the risk of stroke, the researchers found. Compared with never-smokers, the risk of stroke increased:
- 21 percent for those smoking 1--19 cigarettes per day and
- 36 percent for those smoking 20 or more cigarettes per day.
Researchers also analyzed "pack-years," a measure of the number of 20-cigarette packs smoked per day times the number of years smoked. Smoking half a pack daily for 20 years or one pack daily for 10 years would both be calculated as 10 pack-years. They found that, compared with never-smokers, the risk of stroke increased:
- 18 percent for those smoking 1--11 pack-years;
- 25 percent for those smoking 12--26 pack-years; and
- 34 percent for those smoking more than 26 pack-years.
The relationship between the amount of smoking and stroke risk was strongest for ischemic stroke, caused when a blood clot blocks the circulation of blood to part of the brain. Participants who smoked a pack or more per day were 51 percent more likely to suffer an ischemic stroke.
Researchers found a less significant association between the amount a person had smoked and the risk of hemorrhagic stroke, caused by rupture of a blood vessel in the brain. Smoking a pack or more per day raised the risk of hemorrhagic stroke by 20 percent.
"Of the stroke risk factors that can be modified, cigarette smoking is probably second only to hypertension," He said.
"Anti-smoking campaigns are ongoing, but it is rare to see any anti-smoking message in government-owned television or newspapers. Most Chinese still do not understand the risk associated with cigarette smoking."
Based on relative risk and prevalence of cigarette smoking, authors conclude that prevention and cessation efforts could reduce stroke deaths by almost 5 percent, according to the study.
Participants in the National China Hypertension Study included people from all 30 provinces of mainland China, but this analysis could only be performed on those from the 17 provinces that collected contact information. The researchers found that the complete group was similar to the group analyzed in the initial evaluation.
Co-authors include: Tanika N. Kelly, M.P.H.; Dongfeng Gu, M.D., M.Sc.; Jing Chen, M.D.; Jian-feng Huang, M.D.; Ji-chun Chen, M.D.; Xiufang Duan, M.D.; Xigui Wu, M.D.; and Chung-Shiuan Chen, M.S.
The study was supported by the American Heart Association; the National Heart, Lung, and Blood Institute; the Chinese Ministry of Health and the Chinese Academy of Medical Sciences.
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