EVIDENCE ON THE EFFECTS OF GIVING UP CIGARETTE SMOKING

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.

Disability and cognitive impairment are risk factors for pneumonia-related mortality in older adults

The role of functional and cognitive limitations in the risk of pneumonia-related mortality in older adults was examined. As part of a cohort study in 3 communities (East Boston, MA; New Haven, CT; and Iowa and Washington Counties, IA), 6,234 women and 4,035 men ages 65 or older completed baseline interviews between 1981 and 1983 and were followed for up to 6 years. Sex-specific Cox proportional-hazards regression models were used to examine the association of baseline physical and cognitive functioning with report of pneumonia (ICD9 480-486) as an underlying, immediate, or contributing cause of death. During followup, a total of 243 men and 160 women died with pneumonia. Adjusting for age, race, education, evidence of five chronic diseases, and smoking status, a significantly increased risk of pneumonia mortality (P < 0.05) was found for limitations in activities of daily living and cognitive impairment among both men and women. Inability to walk a half mile, climb stairs, or perform heavy housework was significantly associated with increased risk of pneumonia mortality for women but not for men in the same multivariate models. Men and women whose body-mass index was above the median had significantly lower risk of pneumonia mortality compared with those in the lowest quartile. Further elucidation of the sequence between physical and cognitive impairment and risk of pneumonia will be important in reducing pneumonia-associated morbidity and mortality.

Iron miners--a ten year follow-up

1167 workers of Lorraine (France) iron mines, a random sample of 5600 workers aged 35 to 55 years, at work in 1975 constituted the initial cohort that was examined twice at 5-year intervals after the first examination. A questionnaire on respiratory symptoms and smoking habits (MRC questionnaire) plus questions on the work history of each participant was completed, vital capacity (VC), forced expiratory volume in one second (FEV1.0), residual volume (RV) and fractional uptake of CO (FuCO) were measured at the first examination and repeated five and ten years later. At the end of the ten year follow-up, 522 subjects were re-examined, 186 were lost to follow-up, 328 answered a mail questionnaire, and 111 had died. The total number of deaths was not different from that of the general population, but for lung cancer the standardized mortality ratio (SMR) was significantly increased (SMR = 3.7). For the miners re-examined, frequency of bronchitis and decrease of functional tests were more related to age and smoking habits than to occupation.

The impact of quitting smoking on symptoms of chronic bronchitis: results of the Scottish Heart Health Study

Scotland has high rates of death from diseases of the respiratory system and high rates of smoking, especially among women. Data on self reported smoking and prevalence of chronic cough and chronic phlegm among 10,359 men and women aged 40-59 years were obtained from the Scottish Heart Health Study. Overall, current cigarette smokers had rates of chronic cough and chronic phlegm four to five times those of never smokers after standardisation for age (32.3% v 6.5% for men and 24% v 5.5% for women for chronic cough; 31% v 8.3% for men and 21% v 5.5% for women for chronic phlegm). Ex-smokers' symptom rates were a little above those of never smokers and were significant for chronic cough among women and chronic phlegm among men. Men had higher symptom rates than women and this was true for smokers, ex-smokers, and never smokers. The higher rates among men could not be explained by higher cotinine concentrations. Tests to detect "deceivers" among ex-smokers and never smokers using biochemical validation suggested that 87 (1.5%) respondents were in fact smoking; they were excluded from analyses. There were substantially lower rates of chronic cough and chronic phlegm within a year of stopping smoking, and two to four years after stopping 89-99% of the difference between current smokers and never smokers was accounted for (99% and 93% for men and women with chronic cough, 96% and 89% for men and women with chronic phlegm). Even 10 years after stopping, rates of symptoms among ex-smokers remained a little above those of never smokers (except for women with chronic phlegm), though these differences were not statistically significant. Former heavy smokers continued to have rates of chronic cough and chronic phlegm that were higher than those of former light and moderate smokers (though not significantly so). These are cross sectional data, but they emphasise the importance for chronic bronchitis symptoms of giving up cigarette smoking, though the amount previously smoked continues to exert a small influence.

Oral N-acetylcysteine speeds reversal of cigarette smoke-induced mucous cell hyperplasia in the rat

We set out to determine whether or not the "mucolytic" drug N-acetylcysteine would speed the reversal of cigarette smoke-induced secretory-cell hyperplasia to normal, similar to that found previously for two nonsteroidal antiinflammatory drugs. Cigarette smoke alone significantly (p less than 0.01) increased the number of secretory cells in seven out of eight airway levels studied and maintained a significant increase in five of the levels at least 3 weeks after cessation of exposure. Treatment of rats with N-acetylcysteine, as 1% of their drinking water during the recovery period, reduced the time taken for secretory cell number to return to normal to between 4 days and 3 weeks, depending on airway level.

Indomethacin and flurbiprofen speed recovery of rat bronchial epithelium after exposure to cigarette smoke

The cigarette smoke-induced rat model of chronic bronchitis was used to study the time course of the return of cigarette smoke-induced secretory cell hyperplasia to the normal and the capacity of two non-steroidal anti-inflammatory drugs to speed this recovery. Cigarette smoke alone significantly increased (P less than 0.05) the number of secretory cells in all of the eight airway levels studied to between 52-225% above control values. After cessation of exposure, recovery was complete by 9 days in the trachea, between 10-21 days in 'proximal' intrapulmonary airways and 43-84 days in distal bronchioli. Indomethacin and flurbiprofen, given by intraperitoneal injection at 4 mg/kg body weight for 21 days of the recovery period, significantly reduced the time taken for recovery to between 4 and 9 days in intrapulmonary airways but had no effect in the trachea.