Summary of a Canadian Study of Smoking and Health

The object of this study was to investigate the relationship between residence, occupation and smoking habits, and mortality from chronic diseases, particularly lung cancer. It was a prospective study, initiated by a questionnaire sent to Canadian veteran pension recipients. The study was based on the replies of 78,000 males and 14,000 females, together with data on the deaths occurring among these respondents over a six-year follow-up period—July 1, 1956 to January 30, 1962.

The outstanding finding of this study was that cigarette smokers compared to non-smokers had excessive mortality, particularly from heart and circulatory diseases, lung cancer, and bronchitis and emphysema. The mortality ratios for heart and circulatory diseases were elevated even for those who smoked cigarettes less than five years, and remained relatively constant as the duration of smoking increased. The mortality ratios for lung cancer increased markedly as the duration of smoking increased. A small excess in mortality was noted among urban residents. An association between cause of death and occupation was not evident in this study.

Findings based on the data on smoking collected in this study were incorporated into the Report of the U.S. Surgeon-General's Advisory Committee on Smoking and Health.

     

Deaths in Canada from lung cancer due to involuntary smoking.

Recently published evidence indicates that involuntary smoking causes an increased risk of lung cancer among nonsmokers. Information was compiled on the proportion of people who had never smoked among victims of lung cancer, the risk of lung cancer for nonsmokers married to smokers and the prevalence of such exposure. On the basis of these data we estimate that 50 to 60 of the deaths from lung cancer in Canada in 1985 among people who had never smoked were caused by spousal smoking; about 90% occurred in women. The total number of deaths from lung cancer attributable to exposure to tobacco smoke from spouses and other sources (mainly the workplace) was derived by applying estimated age- and sex-specific rates of death from lung cancer attributable to such exposure to the population of Canadians who have never smoked; about 330 deaths from lung cancer annually are attributable to such exposure.     

Modifying risk of developing lung cancer by changing habits of cigarette smoking

Data from a hospital based case-control study of lung cancer in Western Europe were used to examine changes in the risk of developing lung cancer after changes in habits of cigarette smoking. Only data for subjects who had smoked regularly at some time in their lives were included. The large size of the study population (7181 patients and 11 006 controls) permitted precise estimates of the effect of giving up smoking. Risks of developing lung cancer for people who had given up smoking 10 or more years before interview were less than half of those for people who continued to smoke. The reduction in risk was seen in men and women and in former smokers of both filter and non-filter cigarettes but varied by duration of smoking habit before giving up. The protective effect of giving up became progressively greater with shorter duration of smoking habit. The risks after not smoking for 10 years for both men and women who had previously smoked for less than 20 years were roughly the same as those for lifelong non-smokers. Reducing the number of cigarettes smoked a day or switching from non-filter to filter cigarettes also lowered the risk of developing lung cancer but not to the extent associated with giving up smoking.     

Patterns of tobacco smoking in Australia.

A large representative sample of Australians aged 14 years or more was interviewed about smoking. Forty-one per cent of the males and 29% of the females aged 16 years and over currently smoked cigarettes. Smoking rates for both sexes were highest in the 20 to 24 years age group. People in metropolitan areas smoked more than those in rural areas. There was a clear excess of smoking among British immigrants. Higher socioeconomic level was associated with lower smoking rates, with higher ex-smoking rates and with more frequent choice of low-tar brands. Low-tar cigarrettes were used more where health education had emphasized the importance of tar content. Choice of brands among young smokers appeared related to the advertising strategies employed by cigarette companies. The majority of ex-smokers over 60 years of age had given up more than five years previously. Although comparison with earlier surveys of smoking habits is difficult, the results suggested a decrease in cigarette smoking among males and a slight increase among females.     

Lung cancer mortality among nonsmoking uranium miners exposed to radon daughters

Radon daughters, both in the workplace and in the household, are a continuing cause for concern because of the well-documented association between exposure to radon daughters and lung cancer. To estimate the risk of lung cancer mortality among nonsmokers exposed to varying levels of radon daughters, 516 white men who never smoked cigarettes, pipes, or cigars were selected from the US Public Health Service cohort of Colorado Plateau uranium miners and followed up from 1950 through 1984. Age-specific mortality rates for nonsmokers from a study of US veterans were used for comparison. Fourteen deaths from lung cancer were observed among the nonsmoking miners, while 1.1 deaths were expected, yielding a standardized mortality ratio of 12.7 with 95% confidence limits of 8.0 and 20.1. These results confirm that exposure to radon daughters in the absence of cigarette smoking is a potent carcinogen that should be strictly controlled.     

Trends in mortality among California physicians after giving up smoking: 1950-79

A study was conducted to assess how lung cancer and other mortality trends among California physicians had been influenced by the high proportion who had given up smoking since 1950. Several sample surveys indicated that the proportion of California physicians who currently smoked cigarettes had declined dramatically from about 53% in 1950 to about 10% in 1980. During the same period the proportion of other American men who smoked cigarettes had declined only modestly, from about 53% to 38%. Using the 1950 American Medical Directory a cohort of 10 130 California male physicians was established and followed up for mortality till the end of 1979, during which time 5090 died. The information from follow up and death certification was exceptionally good. The standardised mortality ratio for lung cancer among California male physicians relative to American white men declined from 62 in 1950-9 to 30 in 1970-9. The corresponding decline in standardised mortality ratio was from 100 to 63 for other smoking related cancer, from 106 to 71 for ischaemic heart disease, and from 62 to 35 for bronchitis, emphysema, and asthma. The standardised mortality ratio remained relatively constant for other causes of death not strongly related to smoking. The overall ratio declined in all age groups at a rate of about 1% a year. The total death rate among all physicians converged towards the rate among non-smoking physicians. By the end of the study period physicians had a cancer rate and total death rate similar to or less than those among typical United States non-smokers. This "natural experiment" shows that lung cancer became relatively less common on substantial elimination of the primary causal factor, cigarette smoking. Other smoking related diseases also became relatively less common, though factors other than cigarette smoking may have contributed to this change.     

Australian patterns of tobacco smoking in 1986

A total of 9440 Australian men and women of over 15 years of age was interviewed at home in 1986 to determine the prevalence and consumption levels of tobacco products. Current smokers were defined as those who smoked any combination of cigarettes, cigars or pipes regularly. The percentage of current smokers among men was 32.9% and among women was 28.5%, and the peak prevalence of smoking was in the age-group 20-24 years for both men (40.5%) and women (40.8%). Among men, 27.7% were past smokers, and among women, 16.5% were past smokers. The proportion of past smokers among those who had ever smoked was higher in men (0.46) than among women (0.37), but in the younger age groups there was no relative excess among men. Male smokers consumed more cigarettes per day than did female smokers and men were exposed to a higher daily average amount of cigarette tar. Sociodemographic variables that were associated with smoking in both men and women included age and educational and occupational level. Asian-born persons had a significantly lower prevalence of smoking than did persons who were born in Australia.     

Respiratory effects of non-tobacco cigarettes

Data from the Tucson epidemiological study of airways obstructive disease on smoking of non-tobacco cigarettes such as marijuana were analysed to determine the effect of such smoking on respiratory symptoms and pulmonary function. Among adults aged under 40, 14% had smoked non-tobacco cigarettes at some time and 9% were current users. The prevalence of respiratory symptoms was increased in smokers of non-tobacco cigarettes. After tobacco smoking had been controlled for men who smoked non-tobacco cigarettes showed significant decreases in expiratory flow rates at low lung volumes and in the ratio of the forced expiratory volume in one second to the vital capacity. This effect on pulmonary function in male non-tobacco cigarette smokers was greater than the effect of tobacco cigarette smoking. These data suggest that non-tobacco cigarette smoking may be an important risk factor in young adults with respiratory symptoms or evidence of airways obstruction.     

Studies in the distribution of body fat. III. Effects of cigarette smoking

Cross-sectional associations between smoking habits, body mass index, and waist-hip ratio (WHR) were examined in 1122 men aged 19 to 102 years. Weight and body mass index were significantly lower in cigarette smokers than in nonsmokers when age was taken into account. The WHR in smokers was significantly higher than in nonsmokers. A graded dose-response relationship was found between the number of cigarettes smoked and the WHR. Longitudinal associations between changes in smoking habits and changes in the WHR were examined during follow-up visits. In the period between these pairs of visits, weight increased when subjects quit smoking and decreased when they started smoking, as expected. The increase in WHR among those who quit smoking was, however, significantly less than the expected increase if smoking had continued. The WHR in those who started smoking actually increased despite their loss of weight. These paradoxical changes in WHR indicate that there are harmful effects of cigarette smoking on the pattern of distribution of body fat. These facts introduce still another reason to suggest that the decision to initiate or to continue smoking to control body weight is unwise.     

Inhaling and lung cancer: an anomaly explained

An objective index of inhaling cigarette smoke based on carboxyhaemoglobin concentrations and the carbon monoxide yields of cigarettes was used to investigate possible systematic differences in the extent of inhaling among light and heavy smokers when classified according to their self described inhaling habits. A total of 2108 men who smoked cigarettes were studied. Heavy smokers (20 or more cigarettes a day) had a higher average inhaling index than light smokers (fewer than 20 cigarettes a day) both among those who said that they inhaled and among those who said that they did not. This observation, together with indirect evidence that heavy smokers who inhale deeply may to some extent avoid depositing smoke condensate on their main bronchial epithelium, explains a hitherto unresolved anomaly--namely, that the risk of lung cancer is less among heavy cigarette smokers who say that they inhale than it is among those who say that they do not inhale.     

Smoking prevalence and associated risk factors in Canadian adults. Canadian Heart Health Surveys Research Group.

OBJECTIVE: To describe the prevalence and patterns of smoking among Canadian adults, the relation of smoking to other cardiovascular disease risk factors and the awareness of the causes of heart disease. DESIGN: Population-based cross-sectional surveys. SETTING: Nine Canadian provinces, from 1986 to 1990. PARTICIPANTS: A probability sample of 26,293 men and women aged 18 to 74 was selected from the health insurance registries in each province. Of these, 20,585 completed a questionnaire on smoking habits during a home interview. MAIN RESULTS: Approximately 29% of the Canadian population 18 years of age and over were regular cigarette smokers, and over 13% of regular smokers smoked more than 25 cigarettes per day. The proportion of women who had never smoked was higher (37%) than men (24%), except for young women aged 18 to 24. For all participants, there was a lower prevalence of high blood pressure and overweight among smokers than non-smokers. The prevalence of sedentary lifestyle, diabetes and elevated blood cholesterol was positively associated with smoking. The proportion of subjects who identified smoking as a cause of heart disease was higher among smokers, and over 90% believe that heart disease is preventable. CONCLUSION: Because smoking is positively associated with other cardiovascular risk factors, multifactorial and comprehensive approaches are needed in the implementation of cardiovascular disease prevention programs. Knowledge regarding the heart health hazards of smoking is high even among smokers. Motivational approaches that go beyond health risk messages are needed in cessation programs.     

Lung function in an Australian population: 2. Spirometric performance and cigarette-smoking habits.

The FEV1, FVC and FEV1/FVC% in 12016 females and 18 359 males were related to cigarette-smoking habits. Over all, non-smokers had significantly better lung function than cigarette smokers. Ex-smokers of either sex had significantly higher FEV1 and FEV1/FVC% than cigarette smokers, but the FVC values were higher only in females. With consumption in excess of 10 cigarettes per day, deterioration in lung function was manifest in both sexes, but was greater in males than females. The mean chronological age of males who smoked from 30 to 50 cigarettes per day was 12.9 years and 9.6 years less than would have been predicted on the basis of their FEV1 and FVC values respectively. The corresponding values in women were 9.3 years and 7.9 years respectively. Additionally, the deterioration in lung function with increasing age was greater in cigarette smokers than in non-smokers.     

Blood carboxyhaemoglobin, plasma thiocyanate, and cigarette consumption: implications for epidemiological studies in smokers

Carboxyhaemoglobin and plasma thiocyanate concentrations were found to be significantly correlated with self-reported daily cigarette consumption in 360 smokers (r = 0.416 and 0.412 respectively; p less than 0.001). The extent to which inhalation patterns affected the intake of cigarette smoke constituents was determined from the partial correlation between carboxyhaemoglobin and plasma thiocyanate concentrations after the number of cigarettes smoke per day had been allowed for (r = 0.48). Thus 23% of the variation in carboxyhaemoglobin and thiocyanate concentrations was accounted for by the was a cigarette was smoked and a further 21% by the number smoked a day. Furthermore, the relation between carboxyhaemoglobin or plasma thiocyanate and daily cigarette consumption was not linear but reached an asymptote at consumption rates above 25 cigarettes a day. These results suggest that by itself daily cigarette consumption will not identify those smokers most at risk and will also underestimate and dose-response relationship between smoking and selected diseases.     

Health Education and Cigarette Smoking: A Report on a Three-Year Program in the Winnipeg School Division, 1960-1963

The smoking habits of Winnipeg school students were surveyed before and after a three-year program of health education on the hazards of smoking, directed to 8300 out of 48,000 students. The program consisted of informal approaches to students in elementary schools and a formal program of talks, lectures, films, and student participation for older students.

There were fewer students at all ages who had never smoked a cigarette at the time of the second survey. There was a slight decrease in the number of regular smokers in high school, most marked in the school where the program was enthusiastically received and student participation was most active. A direct relationship between parental smoking and that of the student, and an inverse relationship between academic achievement and student smoking, were shown on both surveys. The majority of students believed that smoking caused lung cancer and other hazards to health, although this was less marked among smokers.

The results indicated that an intensive program of health education directed to the teenagers in school was a potentially useful approach to the problem of cigarette smoking.

     

Laryngeal cancer and alcohol consumption in Australia.

Whereas lung cancer is strongly associated with cigarette smoking, and upper alimentary tract cancers with both alcohol and cigarettes, the situation has been less clear-cut for laryngeal cancer. This century's time trends in laryngeal cancer death rates in Australia follow those of oesophageal cancer rather than lung cancer. Further, the trends correlate with those for alcohol consumption rather than cigarette consumption. The separate analyses of trends in age-specific death rates for men and women reveal a pattern of laryngeal cancer risk variation between successive generations which is consistent with a causal role of alcohol consumption. Biological mechanisms, and synergism, between alcohol and cigarette consumption are discussed.     

Smoke exposure in pipe and cigar smokers. Serum thiocyanate measures

Pipe or cigar smoking traditionally has been considered a less risky alternative to cigarette smoking. Some surveys and experimental studies have suggested, however, that former cigarette smokers who switch to cigars and/or pipe (CP) are more likely to inhale then CP users who never smoked cigarettes; but this relationship has not been consistently noted. To clarify smoke-exposure levels from CP smoking, smoking histories and serum thiocyanate (SCN) levels were studied in 9,106 adults aged 25 to 74 years in population-based surveys of seven upper Midwestern communities. Analyses of the 306 male CP smokers indicated a significantly higher SCN level in the ex-cigarette-smoking CP users vs the CP users who never smoked cigarettes. Serum thiocyanate levels of both CP groups were significantly higher than those of nonsmokers and lower than cigarette-only smokers. However, the number of pipe bowls or cigars smoked per day was also significantly related to SCN levels, and this could account for much of the association between SCN and previous cigarette smoking status. Individuals currently smoking four or more pipe bowls or four or more cigars per day had an elevated smoke exposure equivalent to about ten cigarettes per day, whether or not they previously smoked cigarettes. Because of these findings and because former cigarette smokers were more likely to report heavy CP usage, cigarette smokers should be advised to quit rather than to switch to a pipe or cigar.     

Cigarette smoking among school children in Singapore. Part II--Development of the smoking habit

The second in this series on smoking among school children in Singapore aims to define the characteristics of young smokers. Results show that of respondents who had ever smoked, the median age of experimentation with smoking was 12 years. This was seen among boys as well as girls. The median age at which current smokers went on to smoke regularly was 14 years, approximately two years after trying their first cigarette. Friends and parents were the main sources of the first cigarette for all categories of smokers, whether they be ex smokers, experimenters or current smokers. Among the reasons as to why current smokers smoked, the leading two were "to relax" (46.4%) and "out of sheer curiosity" (22.3%). Boys tend more to smoke with friends of the same sex (40.6%) whilst girls preferred mixed company (45.5%) when they smoked. Fathers played a major role in the development and continuation of smoking among those who had ever smoked before--52.0% of boys and 51.6% of girls currently smoking reported that their fathers smoked as well.     

Mortality rates among employees potentially exposed to chrysotile asbestos at two automotive parts factories.

A study of the mortality rates among 1657 employees at two Ontario automotive parts factories that manufactured friction materials containing chrysotile asbestos was initiated in response to the workers' concerns about the effects of asbestos on their health. A total of 1194 men and 258 women had had their first potential exposure at least 10 years before the end of the study period; 563 of the men and 138 of the women had had such an exposure at least 20 years before the end of the study period. A significantly increased rate of death from laryngeal cancer and an elevated rate of death from lung cancer were observed in a cohort analysis. One or two deaths might have been due to pleural mesothelioma. There was no increase in the rate of death from gastrointestinal cancer or from nonmalignant respiratory disease. Case-control analysis showed no association between the risk of laryngeal or lung cancer and the total duration of employment (a surrogate for the extent of ambient exposure to asbestos or other workplace toxic substances) or employment in departments where asbestos had been used. An association between risk of death and occupational exposure is uncertain.     

Carbon monoxide yield of cigarettes and its relation to cardiorespiratory disease

Estimates of the carbon monoxide yield of their cigarettes have been obtained for 4910 smokers (68% of all smokers) in the Whitehall study of men aged 40 to 64. In the 10 years after examination 635 men died. When men smoking cigarettes with high carbon monoxide yield were compared with those smoking cigarettes with a low yield, and after adjusting for age, employment grade, amount smoked, and tar yield, the risk of death was 32% lower for coronary heart disease, 49% higher for lung cancer, and 10% lower for total mortality; these differences were not statistically significant. Among men who said that they inhaled the risk of fatal coronary heart disease was 51% lower in the high carbon monoxide group (p less than 0.01), while the risk of lung cancer was 75% higher. These results provide no evidence that a smoker can reduce his risk of death by smoking a brand with a low carbon monoxide yield; he might even increase it. The complex interactions between characteristics of the smoker, smoking behaviour, constituents of tobacco smoke, and health are again demonstrated.     

Risk of death due to hepatocellular carcinoma among smokers and ex-smokers. Univariate analysis of JACC study data

Hazard ratios (HR) of death due to hepatocellular carcinoma (HCC) were analyzed by gender and age strata (40-59 and 60-79) among smokers and ex-smokers in 65,528 eligible subjects from a large cohort of males and females aged 40-79 years, based on information about several smoking-related characteristics. Both current smokers and ex-smokers among total older males had hazard ratios (HR) for dying from HCC that were 2 to 4 times higher than those who had never smoked at the baseline survey. When subjects were restricted to those without history of liver disease (LD), older male (60-79) ex-smokers presented a statistically significant HR of 5.0. Earlier age at start of smoking (15 to 19) showed a significantly increased HR of 4 to 8 for both current and ex-smokers. Moderate number of cigarettes smoked per day showed an increased HR, and later age at cessation of smoking had a higher HR compared to earlier cessation. Larger cumulative amount of smoking resulted in an elevated HR of 11 times than in those who had never smoked. Cigarette smoking was suggested to be an important risk factor for death from HCC regardless of whether the smoking habit was in the past or was continuing at present. To eliminate confounding effects and interaction with other risk factors of HCC and to clarify the net association between smoking habits and HCC, farther careful analysis using multivariate models is needed.