Carbon monoxide yield of cigarettes and its relation to cardiorespiratory disease

Systematic review with meta-analysis of the epidemiological evidence in the 1900s relating smoking to lung cancer

BACKGROUND

Smoking is a known lung cancer cause, but no detailed quantitative systematic review exists. We summarize evidence for various indices.

METHODS

Papers published before 2000 describing epidemiological studies involving 100+ lung cancer cases were obtained from Medline and other sources. Studies were classified as principal, or subsidiary where cases overlapped with principal studies. Data were extracted on design, exposures, histological types and confounder adjustment. RRs/ORs and 95% CIs were extracted for ever, current and ex smoking of cigarettes, pipes and cigars and indices of cigarette type and dose-response. Meta-analyses and meta-regressions investigated how relationships varied by study and RR characteristics, mainly for outcomes exactly or closely equivalent to all lung cancer, squamous cell carcinoma ("squamous") and adenocarcinoma ("adeno").

RESULTS

287 studies (20 subsidiary) were identified. Although RR estimates were markedly heterogeneous, the meta-analyses demonstrated a relationship of smoking with lung cancer risk, clearly seen for ever smoking (random-effects RR 5.50, CI 5.07-5.96) current smoking (8.43, 7.63-9.31), ex smoking (4.30, 3.93-4.71) and pipe/cigar only smoking (2.92, 2.38-3.57). It was stronger for squamous (current smoking RR 16.91, 13.14-21.76) than adeno (4.21, 3.32-5.34), and evident in both sexes (RRs somewhat higher in males), all continents (RRs highest for North America and lowest for Asia, particularly China), and both study types (RRs higher for prospective studies). Relationships were somewhat stronger in later starting and larger studies. RR estimates were similar in cigarette only and mixed smokers, and similar in smokers of pipes/cigars only, pipes only and cigars only. Exceptionally no increase in adeno risk was seen for pipe/cigar only smokers (0.93, 0.62-1.40). RRs were unrelated to mentholation, and higher for non-filter and handrolled cigarettes. RRs increased with amount smoked, duration, earlier starting age, tar level and fraction smoked and decreased with time quit. Relationships were strongest for small and squamous cell, intermediate for large cell and weakest for adenocarcinoma. Covariate-adjustment little affected RR estimates.

CONCLUSIONS

The association of lung cancer with smoking is strong, evident for all lung cancer types, dose-related and insensitive to covariate-adjustment. This emphasises the causal nature of the relationship. Our results quantify the relationships more precisely than previously.

White cells count in smokers affected by rheumatic diseases

Evidence shows that tobacco smoking interacts with development of rheumatic diseases. Increase in white cells count (leukocytosis) is frequently present, and in smokers, it is considered a biomarker of cardiovascular risk. Aim of the study is to evaluate this biomarker in smokers with rheumatic diagnosis. We carried out an observational study on 115 rheumatic outpatients (26 men and 89 women) divided into two groups according to their smoking habit: one composed of 56 smokers, the other of 59 not smokers. Diagnosis and common routinary clinical parameters were collected. In the total sample, smokers were 48.69%. Most common diagnosis was osteoarthritis (OA) (40.87% of the total); smokers in OA women were 36.11%, smokers in OA men were 54.55%. Second most common diagnosis was rheumatoid arthritis (RA) (23.48% of the total); smokers in RA women were 40.91%; smokers in RA men were 80%. OA smokers showed a significant increase (P < 0.05) in white cells count when compared with OA not smokers. Between RA smokers and not smokers, any clinical difference was found. RA subjects following regular pharmacological treatment in the last 2 months were 84.61%. OA patients treated with drugs in the last 2 months were only 22.2%. Results seem to confirm that smoking habit may influence the development as well as gender distribution of rheumatic diseases. They show also that in absence of pharmacological treatment in smokers affected by OA leukocytosis (biomarker of cardiovascular risk) is observed.

Clinical trials methods for evaluation of potential reduced exposure products

Potential reduced exposure products (PREPs) to tobacco toxicants may have promise in reducing tobacco-related morbidity or mortality or may promote greater harm to individuals or the population. Critical to determining the risks or benefits from these products are valid human clinical trial PREP assessment methods. Such an assessment involves determining the effects of these products on biomarkers of exposure and effect, which serve as proxies for harm, and assessing the potential for consumer uptake and abuse of the product. This article identifies critical methodologic issues associated with PREP assessments, reviews the methods that have been used to assess PREPs, and describes the strengths and limitations of these methods. Additionally, recommendations are provided for clinical trial PREP assessment methods and future research directions in this area based on this review and on the deliberations from a National Cancer Institute sponsored Clinical Trials PREP Methods Workshop.

Cardiovascular biomarkers in groups of established smokers after a decade of smoking

To investigate tools for evaluation of smoking-associated disease initiation and progression, we examined basic clinical parameters and biomarkers of cardiovascular disease risk, in a group of healthy volunteers with an average 10-year smoking history. A small cross-sectional study of never-smokers, moderate smokers and smokers was performed. Caucasians were recruited to match pre-defined cigarette tar yields and cigarettes smoked per day. For haematological parameters, significant differences between never-smokers and all female smokers combined were seen for haemoglobin concentration, haematocrit, total leucocyte count, neutrophil count and lymphocyte count. For all male smokers combined, only total leucocyte count was statistically different. Analysis of exhaled CO and other smoke exposure biomarker (nicotine and its metabolites) data showed a statistically significant increase in all groups of smokers with a trend related to the number of cigarettes smoked per day. Thromboxane urinary metabolites 11-dehydro-thromboxane B(2) and 2,3-dinor-thromboxane B(2) were statistically significantly elevated in smokers. Significant statistical differences between smokers with approximately 10 years of smoking history and non-smokers in white cells count, hemoglobin and thromboxane turnover were seen, although they did not reach levels associated with overt diseases. These data could provide insight into early biomarkers predictive of risk for coronary and vascular disease.

Carboxyhaemoglobin levels and their determinants in older British men

Background

Although there has been concern about the levels of carbon monoxide exposure, particularly among older people, little is known about COHb levels and their determinants in the general population. We examined these issues in a study of older British men.

Methods

Cross-sectional study of 4252 men aged 60–79 years selected from one socially representative general practice in each of 24 British towns and who attended for examination between 1998 and 2000. Blood samples were measured for COHb and information on social, household and individual factors assessed by questionnaire. Analyses were based on 3603 men measured in or close to (< 10 miles) their place of residence.

Results

The COHb distribution was positively skewed. Geometric mean COHb level was 0.46% and the median 0.50%; 9.2% of men had a COHb level of 2.5% or more and 0.1% of subjects had a level of 7.5% or more. Factors which were independently related to mean COHb level included season (highest in autumn and winter), region (highest in Northern England), gas cooking (slight increase) and central heating (slight decrease) and active smoking, the strongest determinant. Mean COHb levels were more than ten times greater in men smoking more than 20 cigarettes a day (3.29%) compared with non-smokers (0.32%); almost all subjects with COHb levels of 2.5% and above were smokers (93%). Pipe and cigar smoking was associated with more modest increases in COHb level. Passive cigarette smoking exposure had no independent association with COHb after adjustment for other factors. Active smoking accounted for 41% of variance in COHb level and all factors together for 47%.

Conclusion

An appreciable proportion of men have COHb levels of 2.5% or more at which symptomatic effects may occur, though very high levels are uncommon. The results confirm that smoking (particularly cigarette smoking) is the dominant influence on COHb levels.

Does increased cigarette consumption nullify any reduction in lung cancer risk associated with low-tar filter cigarettes?

Epidemiological data suggest that smoking filter and lower tar cigarettes is associated with less lung cancer risk than is smoking plain and higher tar cigarettes. A recent National Cancer Institute monograph claimed these apparent benefits of lower delivery products may be illusory if relative risks are adjusted for daily consumption, and switching leads to "compensation" for reduced nicotine intake by increasing numbers of cigarettes smoked. To investigate this, we compared relative risks unadjusted and adjusted for daily cigarette consumption. Overall estimates of the filter/plain relative risk, using random-effects meta-analysis, were 0.61 (95%confidence interval 0.54 to 0.70) for unadjusted data and 0.66 (0.58 to 0.76) for adjusted data. The lower tar/higher tar relative risk was estimated as 0.60 (0.45 to 0.81) for unadjusted data and 0.73 (0.64 to 0.83) for adjusted data. The risk reductions were clearly seen regardless of gender, study location, period, or design, and when only studies providing both unadjusted and adjusted estimates were considered. Whether or not relative risk estimates are adjusted for cigarette consumption is not crucial to the conclusion of a clear advantage to filter cigarettes and tar reduction. Data on "compensation" for amount smoked were reviewed and any increase following switching to reduced-tar-yield cigarettes was shown to be quite small. Other biases in the epidemiology are also discussed, and we conclude that the apparent advantage to reduced-tar-delivery products is real and likely to be a marked underestimate of the reduction in lung cancer risk from lifetime smoking of low-tar cigarettes.

Cigarette tar yields in relation to mortality from lung cancer in the cancer prevention study II prospective cohort, 1982-8

OBJECTIVE

To assess the risk of lung cancer in smokers of medium tar filter cigarettes compared with smokers of low tar and very low tar filter cigarettes.

DESIGN

Analysis of the association between the tar rating of the brand of cigarette smoked in 1982 and mortality from lung cancer over the next six years. Multivariate proportional hazards analyses used to assess hazard ratios, with adjustment for age at enrollment, race, educational level, marital status, blue collar employment, occupational exposure to asbestos, intake of vegetables, citrus fruits, and vitamins, and, in analyses of current and former smokers, for age when they started to smoke and number of cigarettes smoked per day.

SETTING

Cancer prevention study II (CPS-II).

PARTICIPANTS

364 239 men and 576 535 women, aged > or = 30 years, who had either never smoked, were former smokers, or were currently smoking a specific brand of cigarette when they were enrolled in the cancer prevention study.

MAIN OUTCOME MEASURE

Death from primary cancer of the lung among participants who had never smoked, former smokers, smokers of very low tar (< or = 7 mg tar/cigarette) filter, low tar (8-14 mg) filter, high tar (> or = 22 mg) non-filter brands and medium tar conventional filter brands (15-21 mg).

RESULTS

Irrespective of the tar level of their current brand, all current smokers had a far greater risk of lung cancer than people who had stopped smoking or had never smoked. Compared with smokers of medium tar (15-21 mg) filter cigarettes, risk was higher among men and women who smoked high tar (> or = 22 mg) non-filter brands (hazard ratio 1.44, 95% confidence interval 1.20 to 1.73, and 1.64, 1.26 to 2.15, respectively). There was no difference in risk among men who smoked brands rated as very low tar (1.17, 0.95 to 1.45) or low tar (1.02, 0.90 to 1.16) compared with those who smoked medium tar brands. The same was seen for women (0.98, 0.80 to 1.21, and 0.95, 0.82 to 1.11, respectively).

CONCLUSION

The increase in lung cancer risk is similar in people who smoke medium tar cigarettes (15-21 mg), low tar cigarettes (8-14 mg), or very low tar cigarettes (< or = 7 mg). Men and women who smoke non-filtered cigarettes with tar ratings > or = 22 mg have an even higher risk of lung cancer.

Epidemiology of smoking-induced cardiovascular disease

Cigarette smoking is a major cause of coronary heart disease, stroke, aortic aneurysm, and peripheral vascular disease. The risk is manifest both as an increased risk for thrombosis of narrowed vessels and as an increased degree of atherosclerosis in those vessels. The cardiovascular risks owing to cigarette smoking increase with the amount smoked and with the duration of smoking. Risks are not reduced by smoking cigarettes with lower machine-measured yields of tar and nicotine, but those who have only smoked pipes or cigars seem to have a lower risk for cardiovascular diseases. Cessation of cigarette smoking reduces disease risks, although risks may remain elevated for a decade or more after cessation.

Health impact of "reduced yield" cigarettes: a critical assessment of the epidemiological evidence

Cigarettes with lower machine measured "tar" and nicotine yields have been marketed as "safer" than high tar products over the last four decades, but there is conflicting evidence about the impact of these products on the disease burden caused by smoking. This paper critically examines the epidemiological evidence relevant to the health consequences of "reduced yield" cigarettes. Some epidemiological studies have found attenuated risk of lung cancer but not other diseases, among people who smoke "reduced yield" cigarettes compared to smokers of unfiltered, high yield products. These studies probably overestimate the magnitude of any association with lung cancer by over adjusting for the number of cigarettes smoked per day (one aspect of compensatory smoking), and by not fully considering other differences between smokers of "high yield" and "low yield" cigarettes. Selected cohort studies in the USA and UK show that lung cancer risk continued to increase among older smokers from the 1950s to the 1980s, despite the widespread adoption of lower yield cigarettes. The change to filter tip products did not prevent a progressive increase in lung cancer risk among male smokers who began smoking during and after the second world war compared to the first world war era smokers. National trends in vital statistics data show declining lung cancer death rates in young adults, especially males, in many countries, but the extent to which this is attributable to "reduced yield" cigarettes remains unclear. No studies have adequately assessed whether health claims used to market "reduced yield" cigarettes delay cessation among smokers who might otherwise quit, or increase initiation among non-smokers. There is no convincing evidence that past changes in cigarette design have resulted in an important health benefit to either smokers or the whole population. Tobacco control policies should not allow changes in cigarette design to subvert or distract from interventions proven to reduce the prevalence, intensity, and duration of smoking.

Tar yield of cigarettes and risk of acute myocardial infarction. GISSI-EFRIM Investigators

OBJECTIVE

To analyse the relation between tar and nicotine yield of cigarettes smoked in the recent past and the risk of myocardial infarction.

DESIGN

Multicentre case-control study conducted between September 1988 and June 1989.

SETTING

Over 80 coronary care units in various Italian regions.

SUBJECTS

916 patients with acute myocardial infarction without history of ischaemic heart disease and 1106 controls admitted to hospital for acute conditions not related to known or suspected risk factors for ischaemic heart disease.

MAIN OUTCOME MEASURES

Relative risk of myocardial infarction according to type of cigarette smoked adjusted for identified potential confounding factors. Brands of cigarettes classified according to yield of tar and nicotine.

RESULTS

Patients with acute myocardial infarction were more often smokers and among smokers they tended to smoke more cigarettes. Compared with non-smokers their estimated relative risks were 3.8, 4.3, 3.2, and 3.7 in the four categories of tar yield (< 10, 10-15, > 15-20, and > 20 mg, respectively). No trend in risk across yields was evident when analysis was restricted to smokers and allowance was made for number of cigarettes. Compared with risks in subjects in the lowest category of tar yield the relative risks were 1.2, 0.8, and 1.0 for the subsequent yields. Compared with risks in non-smokers the relative risks ranged from 9.3 to 12.6 below the age of 50 but no trend was observed with increasing yield.

CONCLUSIONS

Changing to cigarettes with a lower tar yield is not an effective means of reducing tobacco related morbidity from myocardial infarction.

Coronary heart disease, cancer and mortality in male middle-aged light smokers

We examined the effect of light smoking in relation to incidence of coronary heart disease (CHD) in a general population sample consisting of 6879 men aged 47-55 years and free of previous myocardial infarction (MI) at baseline. After a follow-up of mean duration 11.8 years, 11.0% of men smoking 1-4 cigarettes daily (n = 228) had suffered a major CHD event, compared to 3.7% of non-smokers (n = 2049) [adjusted odds ratio 2.8 (1.7-4.7)]. No further increase in risk was observed in men who smoked more. There was an increasing risk of death from cancer with the number of cigarettes smoked per day. Mortality was increased in all categories of cigarette smokers, particularly among the very heavy smokers, who had a mortality risk of 22% compared to 6% among nonsmokers [adjusted odds ratio 4.4 (2.7-7.1)]. Data from an examination 4 years later considered only those men who stated that their smoking habits were identical on both occasions (n = 3981). Among these subjects the incidence of CHD after a mean period of 7.1 years was 10.6% in men smoking 1-4 cigarettes per day, compared to 2.6% in nonsmokers [adjusted O.R. 4.6 (2.1-10.1)]. No dose-response effect was observed. Even very light cigarette smoking considerably increases the risk of CHD in middle-aged men.

"Low yield" cigarettes and the risk of nonfatal myocardial infarction in women

Newer brands of cigarettes with reduced yields of nicotine and carbon monoxide have been promoted as being less hazardous than others. We evaluated the effect of smoking "low yield" cigarettes on the risk of nonfatal myocardial infarction in women under 65 years of age. The data were obtained in a case-control study of 910 women with a first myocardial infarction and 2375 hospital controls. The estimated relative risk for current smokers as compared with those who had never smoked increased with the number of cigarettes smoked. The estimated overall relative risk was 3.7 (95 percent confidence interval, 3.0 to 4.7). The estimated risks did not vary according to the nicotine or carbon monoxide yield of the cigarette. The estimated relative risk (4.7) in women who smoked brands with the lowest levels of nicotine (less than 0.40 mg per cigarette) was similar to that (4.2) in smokers of the higher-yield brands (greater than 1.30 mg). For exsmokers, the estimated relative risk was 1.4 (95 percent confidence interval, 1.0 to 1.8). These data suggest that women who smoke low-yield cigarettes do not have a lower risk of a first nonfatal myocardial infarction than women who smoke higher-yield brands. For smokers who wish to reduce their risk, switching to low-yield brands is a poor alternative to quitting.

Cigarette consumption and serum cotinine in relation to birthweight

The concentration of serum cotinine (the major metabolite of nicotine) was measured in sera from 4211 women at between 15 and 21 weeks gestation to determine whether a serum cotinine level was a better predictor of low birthweight than the self-reported number of cigarettes smoked per day. Both cotinine levels and smoking history were significantly associated with reduced birthweight, but cotinine correlated significantly better. Smokers of greater than or equal to 25 cigarettes per day, representing the 2.7% of women with the greatest cigarette consumption, had infants 289 g lighter than the 68% of women who were nonsmokers. Women with serum cotinine levels in the top 2.7% (greater than or equal to 284 ng/ml) had infants 441 g lighter than the 68% of women with the lowest cotinine levels (less than or equal to 24 ng/ml). Our results strengthen the evidence linking smoking with low birthweight and also demonstrate that cotinine can be satisfactorily used to assess and monitor cigarette smoking in pregnancy.

Carbon monoxide levels in the breath of smokers and nonsmokers: effect of domestic heating systems

Breath and ambient (room) carbon monoxide (CO) levels were measured in a random sample of 168 adults in their own homes. The levels of breath CO in the 69 smokers ranged from 3 ppm to over 100 ppm, 74% being above 10 ppm; mean levels in the 99 nonsmokers were lower than in the smokers, 79% being below 6 ppm. In the remaining 21% of nonsmokers with higher breath levels than expected, the ambient CO was also found to be elevated, ranging up to 38 ppm. A close correlation in the nonsmokers was found between the breath and ambient CO levels (r = 0.952, p less than 0.001). The rooms with the elevated ambient CO levels (above 5 ppm) were those which, at the time of testing, were being heated by gas radiant heaters, open fires or stoves. The maximum ambient CO in the rooms of smokers with non CO generating heating was 16 ppm. The results suggest that many people, both smokers and nonsmokers, may be at risk from CO generated by certain domestic heating systems and that nonsmokers are far more likely to be exposed to high levels of CO from these sources than from being in a room with a heavy smoker. Poor ventilation associated with the current trend towards excluding all draughts is likely to exacerbate the situation for both smokers and nonsmokers.