| Background and objectivesHypertension and tobacco smoking have been identified as the first and second leading cause of death worldwide, respectively. In China, both hypertension and smoking are major public health challenges because of their high prevalence and concomitant risks of cardiovascular disease (CVD) and all-cause mortality. According to the Global Adult Tobacco Survey conducted during2008-2010in13low-and-middle income countries, the prevalence of current smoking is estimated at about30%. A total of5.4million deaths each year worldwide are attributed to currently tobacco use, and the number is projected to strikingly increase to more than8million by2030.Several studies, attempting to quantify the risk of mortality from CVD and all-cause attributable to smoking, have been conducted in general population in China. To date, only one study was specially conducted in older isolated systolic hypertensive patients. In which, risk estimates were based on a small sample size patients with a short period of follow-up.Hypertension and smoking co-exist more often than expected, which further amplifies risk of CVD and all-cause mortality. The combined effect of blood pressure and smoking on risk of CVD and all-cause mortality has not been well investigated in hypertensive patients. In this report, we examined the effect of tobacco smoking on deaths from CVD and all-causes, as well as to answer the question:whether cigarette smoking exacerbates the effect of blood pressure on the risk of CVD and all-cause mortality among hypertensive patients?Materials and methods36943participants (aged≥40years) were hypertensive patients who took part in the China National Hypertension Survey Epidemiology Follow-up Study. Data on smoking and other variables were obtained in1991and follow-up evaluation was conducted in1999-2000. Smoking was defined as having smoked at least one cigarette per day for at least1year, and1g of tobacco was considered to be equivalent to1cigarette. Cox proportional hazards models were applied to estimate relative risks (RRs) and95% confidence intervals (CIs) for CVD and all-cause mortality in relation to smoking.ResultsDuring a mean follow-up of8.3years,7194deaths (3765men and3429women) were documented in this cohort study. Of these deaths,3785(1978men and1807women) were attributable to CVD. The crude mortality rate was1368.1per100000person-years for CVD and2600.1per100000person-years for all-cause events, respectively. After adjustment for age, sex, education level, body mass index, physical activity, alcohol consumption, urbanization, and geographic region, compared with patients never smoked, the respective RRs (95%CIs) for CVD and all-cause mortality were1.28(1.19,1.38) and1.31(1.24,1.38) for patients who were smokers. The corresponding population attributable risks were9.08%and9.96%, respectively.There was a significant dose response association between smoking and risk of CVD and all-cause mortality in hypertensive patients. In terms of pack-years of smoking, compared with never smokers, the RR (95%CI) of CVD mortality was1.19(1.07,1.32) for light smokers (0.1-19pack years of smoking) and1.34(1.23,1.46) for heavy smokers (≥20pack years of smoking); the corresponding RRs of all cause mortality were1.23(1.14,1.32) and1.36(1.28,1.45)(P for linear trends≤0.001). As for cigarettes smoked per day, the respective RR (95%CI) of CVD mortality was1.30(1.19,1.42) and1.25(1.14,1.37) for those who smoked1-10and>10cigarettes per day; the corresponding RRs of all cause mortality were1.23(1.14,1.32) and1.36(1.28,1.45)(P for linear trends≤0.001). In addition, a significant upward trend was also observed with the total number of years of smoking for risk of CVD and all-cause mortality (P for linear trends≤0.001). A higher risk was observed in hypertensive patients who started smoking in their early life. In stratified analysis according to blood pressure level, the positive dose-response relationship between smoking and risk of CVD and all-cause mortality remained in systolic blood pressure (SBP) groups (140-159and≥160mmHg), diastolic blood pressure (DBP) groups (<90,90-99and≥100mmHg), pulse pressure (PP) groups (50-69, and≥70mmHg) and all stages of hypertension (all P for linear trends≤0.05).In general, a synergistic effect on the risk of CVD and all-cause mortality existed between cigarette smoking and blood pressure category in hypertensive patients. Compared with never smokers with SBP<140mmHg, the RRs (95%CIs) for heavy smokers with SBP≥160mmHg were substantially increased to2.34and3.03for CVD and all-cause mortality, separately. Heavy smokers with DBP≥100mmHg respectively experienced177%and130%excess risk for CVD and all-cause mortality compared to never smokers with DBP<90mmHg. In addition, compared to never smokers with PP <50mmHg, heavy smokers with PP>70mmHg were significantly associated with a122%and183%greater risk of CVD and all-cause mortality, respectively. The respective RRs (95%CIs) for CVD and all-cause mortality were2.31(2.07,2.59) and2.30(1.99,2.65) in heavy smokers with stage2and3hypertension compared with never smokers with stage1hypertension.The dose response relationship existed even after excluding hypertensive patients who were former smokers, taking anti-hypertensive medications within two weeks before baseline, or who died during the first1year of follow-up.ConclusionsSmoking not only significantly increased the risk of CVD and all-cause mortality among hypertensive groups, but the combined effect on the risk of CVD and all-cause mortality existed between cigarette smoking and blood pressure category. Cigarette smoking does exacerbate the effect of blood pressure on the risk of cardiovascular and all-cause mortality in hypertensive patients. Given high prevalences of both smoking and hypertension in China, besides hypertension management, smoking cessation should be an essential component for preventing deaths related to smoking for hypertensive patients. |
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