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Indian Journal of Community Medicine

Smoking, Alcohol Consumption & Coronary Heart Disease - A Risk Factor Study

Author(s): Subrata Bagchi, Ranadeb Biswas*, Uchhal K. Bhadra, Aniruddha Roy**, Malay Mundle, Pradip Kr Dutta***

Vol. 26, No. 4 (2001-10 - 2001-12)

Deptt. of Community Medicine, IPGME&R, Calcutta *Deptt. of PSM, All India Institute of Hygiene & Public Health, Calcutta **Deptt. of Medicine, R.G. Kar Medical College, Calcutta ***Deptt. of Medicine, Calcutta National Medical College, Calcutta

Abstract:

Research question: What is the relationship between smoking, alcohol consumption and CHD?

Objective: To study the association of smoking and alcohol consumption with CHD.

Study design: Case-control. Setting: Medical College Hospital, Calcutta.

Participants: Indoor patients of cardiology and surgery departments.

Sample size: 100(50 cases, 50 controls).

Study variables: Smoking, number of cigarettes smoked, duration of smoking, alcohol consumption.

Outcome variables: CHD.

Statistical analysis: Chi-square test, odds ratio, 95% confidence interval by Taylor Series approximation.

Results: Strong statistical association was found between smoking and CHD (odds ratio 5.06). Risk of CHD increased with number of cigarettes smoked and duration of smoking. No statistical association was found between habit of drinking and CHD.

Keywords: Coronary heart disease (CHD), Smoking, Alcohol

Introduction:

Coronary heart disease (CHD) ranks first as a cause of premature death in industrialized countries. Developing countries are increasingly being exposed to similar experiences as they progress with their socio-economic development1. Multifactorial aetiology in the genesis of CHD is now well understood. In India, over the last two decades, a few epidemiological studies have revealed increasingly high magnitude of CHD with considerable regional variations ranging from 64.8 per thousand2 to 96.7 per thousand3 among urban adults and from 22.8 per thousand to 38 per thousand among rural adult population4. Heavy smoking is responsible for CHD in a good number of cases5. High consumption of alcohol is an important preventable cause of death. There is evidence that the influence of smoking is independent of, but synergistic with, other risk factors. Major effects of smoking on cardiovascular system are stimulation of central nervous system by nicotine and displacement of oxygen from haemoglobin by carbon monoxide. Also, repetitive toxic injury to endothelial cells occurs by smoke, thereby accelerating atherogenesis. Significant proportion of all deaths due to CHD under 65 years of age are attributable to cigarette smoking. It seems to be particularly important in causing sudden death in CHD, especially in men under 50 years of age. On an average, 50 to 150 mcg of nicotine is absorbed through lungs and oral mucosa with each puff of tobacco or about 1 to 2 mg per cigarette. Those who stop smoking show a prompt decline in risk and may reach the risk level of non-smokers as early as after 1 year of cessation. For those who have a myocardial infarction, the risk of fatal recurrence may be halved after cessation of smoking6. While heavy drinking increases mortality, moderate drinking may be beneficial through an increase in HDL or changes in the clotting mechanism. The consumption of two or more ounces of alcohol per day is associated with hypertension and CHD mortality7.

Material and Methods:

The study was conducted in Medical College Hospitals, Calcutta. The participants were indoor patients of cardiology and surgery departments. The study was designed as a case-control type. Fifty cases and fifty pair-matched controls were taken over a period of twelve months in 1997. Persons with history of first ischaemic attack only were included in the study. Data was collected on a pre-designed and pretested proforma. The two variables - smoking and alcohol consumption were analysed in cases and controls to study the risk factors of coronary heart disease. The smokers were stratified according to the number of cigarettes smoked per day and the duration of smoking. Odds ratio for each risk factor was calculated and 95% confidence interval computed from Taylor Series approximation.

Results:

Table I: Distribution of cases and controls by smoking habit (n=100)

Category Cases No. (%) Controls No. (%) Total Odds Ratio 95% CI*
Smoker 32 (64) 13 (26) 45 5.06 -0.86, 31.52
Non-Smoker 18 (36) 37 (74) 55 1  
Total 50 (100) 50 (100) 100    

*Taylor Series approximation; X2=14.58, df=1, p<0.001

Table I shows that 32(64%) cases and 13(26%) controls were smokers. An odds ratio of 5.06 (95% CI:-0.86, 31.52) here means a strong association between smoking and CHD (*2=14.58, df=1, p<0.001).

Table II: Frequency of smoking among cases and controls (n=100)

No. of Cigarettes Cases No. (%) Controls No. (%) Total Odds Ratio 95% CI*
0 18 (36) 37 (74) 55 1  
Upto 20 22 (44) 10 (20) 32 4.52 3.58, 5.46
21-40 10 (20) 3 (6) 13 6.85 5.44, 8.26
Total 50 (100) 50 (100) 100    

*Taylor Series approximation; X2 with Yates' correction=14.45, df=2, p<0.001

Table II shows the classification of study population in three categories according to the frequency of smoking. 22(44%) cases and 10(20%) controls had smoked up to 20 cigarettes per day giving an odds ratio of 4.52 (95% CI: 3.58, 5.46). Similarly, 10(20%) cases and only 3(6%) controls had smoked more than 20 cigarettes daily, giving an odds ratio of 6.85 (95% CI: 5.44, 8.26). Difference in the number of cigarettes smoked by cases and controls was statistically significant (*2 with Yates' correction=14.45, df=2, p<0.001).

Table III: Duration of smoking among cases and controls (n=100)

Duration of Smoking (Years). Cases No. (%) Controls No. (%) Total Odds Ratio 95% CI*
0 18 (36) 37 (74) 55 1  
1- 20 14 (28) 9 (18) 23 3.2 2.19, 4.21
>20 18 (36) 4 (8) 22 9.25 8.03, 10.47
Total 50 (100) 50 (100) 100    

*Taylor Series approximation; X2 with Yates' correction=16.04, df=2, p<0.001

Table III shows that, with an odds ratio of 3.2 (95% CI: 2.19, 4.21), 14(28%) cases and 9(18%) controls had smoked for up to 20 years, while 18(36%) cases and 4(8%) controls smoked for more than 20 years with an odds ratio of 9.25 (95% CI: 8.03, 10.47). Again, the difference in the occurrence of CHD according to the duration of smoking was found to be significant (*2 with Yates' correction=16.04, df=2, p<0.001).

Table IV: Alcohol consumption among cases and controls (n=100)

Category Cases No. (%) Controls No. (%) Total Odds Ratio 95% CI*
Non-Drinking 42 (84) 48 (96) 90    
Drinking 8 (16) 2 (4) 10 4.57 2.97, 6.17
Total 50 (100) 50 (100) 100    

*Taylor Series approximation; X2 with Yates' correction=2.8, df=1, p>0.05

Table IV shows that only 8(16%) cases and 2(4%) controls consumed alcohol occasionally, with an odds ratio of 4.57 (95% CI: 2.97, 6.17), no significant correlation of alcohol with CHD was elicited (*2 with Yates' correction=2.8, df=1, p>0.05).

Discussion:

A statistical association of smoking and coronary heart disease was found (p<0.001). The odds ratio is 5.06. It means that the risk of CHD is 5.06 times greater in smokers than in non-smokers. Alessandro et al also found a strong association of smoking with CHD, odds ratio being 6.758. Sinha et al found similar results2. Compared to non-smokes, odds ratio of occurrence of CHD was 4.52 among cases who smoked up to 20 cigarettes per day and 6.85 among those who smoked more than 20 cigarettes per day, indicating a dose-response relationship. Kaufman et al observed that risk of CHD increased 2.8 times with the number of cigarettes smoked9. Statistical association between the duration of smoking and occurrence of CHD was elicited. Compared to non-smokers, odds ratio of the occurrence of CHD was found 3.2 among cases smoking cigarettes up to 20 years and 9.25 among those who smoked for twenty or more years. All the observed differences were found to be statistically significant at the level of 95% confidence interval.

In this study, no significant statistical association was found between the habit of drinking alcohol and CHD. However, odds ratio for drinking alcohol and occurrence of CHD was 4.57 (95% CI: 2.97, 6.17). Stason et al analysed Framingham study cohorts and found 0.7 as the relative risk of those drinking 30 or more ounces of ethanol per month compared to those drinking less than this10. Dyer et al did not find any association between alcohol intake and CHD11. Rimm et al, however, observed that the relation between alcohol consumption and risk of CHD was causal12.

However, inspite of pair-matched sampling of controls, the inherent limitation of confounding error adversely influencing the results of univariate analysis done in this study cannot be ignored. Interaction or effect modification due to synergism of multiple variables was not explored due to small size of the sample. To obtain the relative importance of various risk factors, multivariate analysis using forward stepdown logistic regression statistical model is recommended for further research.

References:

  1. World Health Organization. Smoking and cardiovascular morbidity. In: TRS 678, Geneva, WHO, 1982.
  2. Sinha PR. Prevalence of CHD in an urban community in Varanasi. IJCM 1990; XV: 82-4.
  3. Chadha SL et al. Epidemiological study of coronary heart disease in urban population of Delhi. IJMR 1990; 92: 424-30.
  4. Dewan BD et al. Epidemiology of coronary heart disease in India. Ind Heart J 1974; 26: 68.
  5. Sinha BC. Pattern of ischaemic heart disease in India. J Ind Med Asson 1970; 55: 171.
  6. Wilhelmsson C. Risk factors of coronary artery disease. Lancet 1975; 1: 415.
  7. Gotto AK. Risk factors of coronary artery disease. In: Braunwald E, ed, Heart disease. W.B. Saunders, 1988; 1153-83.
  8. Alessandro RD. Snoring every night as a risk factor for myocardial infarction - A case-control study. BMJ 1990; 300: 1957.
  9. Kaufman D. Nicotine and carbon monoxide content of cigarette smoke and risk of myocardial infarction in young men. New England J Med 1983; 305: 409.
  10. Stason WB. Alcohol consumption and non-fatal myocardial infarction. American J Epid 1976; 104: 603.
  11. Dyer AR. Alcohol consumption, cardiovascular risk factors and mortality in two Chicago epidemiological studies. Circulation 1977; 56: 1067.
  12. Rimm EB. Prospective study of alcohol consumption and risk of coronary disease in men. Lancet 1991; 338: 464.
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