Discussion
In the present study, HRQL improved significantly during the 3-month follow-up period among smokers who participated in a smoking cessation programme. Our smoking cessation programme improved HRQL not only in quitters but also in continuous smokers; no significant differences existed between quitters and continuous smokers with regard to HRQL improvement. Furthermore, we found that the average nicotine addiction level was associated with a clinically significant improvement in HRQL. These findings highlight an additional effect of smoking cessation treatment not previously discussed.
There is currently little information about potential changes in HRQL that can be provided to smokers who are trying to quit. Several previous studies6 ,8 ,16 showed that smoking cessation leads to improvement in HRQL. Our results support such findings. Therefore, when promoting smoking cessation to smokers, the impact on HRQL is highlighted as well as on longer term disease effects. What then about the quality of life of patients who fail to quit smoking?
There are conflicting findings about HRQL in patients who failed to quit smoking. McClave et al17 found that HRQL outcomes among current smokers who had unsuccessfully attempted to quit were worse than outcomes among former smokers. Croghan et al18 also found that continuous smokers treated for nicotine dependence reported less improvement in HRQL compared with those who stopped smoking. These studies suggested that HRQL in unsuccessful quitters may have been negatively affected by their failure to actually quit smoking. On the other hand, Wiggers et al19 examined the extent to which smoking cessation leads to changes in HRQL in cardiovascular patients. Multilevel modelling showed that generic and disease-specific HRQL in atherosclerotic patients improved significantly. No main differences were found between quitters and smokers in terms of improvement in HRQL. In fact, some subgroups reported a poorer HRQL after smoking cessation. Thus, atherosclerotic patients who quit smoking did not experience more improvement in HRQL compared with those who continued smoking. Quist-Paulsen et al16 reported that quitters and sustained smokers with coronary artery disease had similar improvements in HRQL from baseline to the 12-month follow-up. Similar to these reports (although they relate to patients with specific diseases), our results showed that improvements in HRQL were not significantly different in quitters compared to continuous smokers. Furthermore, after adjustment for comorbidities, the quit status after smoking cessation therapy was not associated with a clinically significant improvement in HRQL. Hays et al20 suggested that the positive impact on HRQL was mediated primarily by abstinence from smoking, but there also appeared to be direct effects of pharmacological treatment (eg, amelioration of withdrawal symptoms) that directly contributed to improved self-control and health transition.
Although the main focus in our study was on smoking cessation, the reduction in smoking in our study was notable. Even continuous smokers reported that the maximal numbers of cigarettes smoked daily during the previous 4 weeks ranged from 1 to 60 (median 5 cigarettes), with a corresponding low median exhaled CO level of 7 ppm, which was comparable to the ‘abstinent range’. This suggested that even though the participants in this group did not quit smoking completely they might have markedly reduced the number of cigarettes smoked. This might have led to an improvement in HRQL similar to the quitters, although changes in exhaled CO levels from baseline to 12 weeks were not related to an improvement in HRQL. Therefore, knowledge of the impact of smoking cessation therapy on HRQL may be important in encouraging smokers to participate in a smoking cessation programme. Improvement in health status or HRQL has been identified as an outcome criterion for the effectiveness of treatment for addictions.21
Furthermore, we found that after adjustment for baseline characteristics and comorbidities, the average nicotine addiction level was associated with a clinically significant improvement in HRQL. To the best of our knowledge, this is the first study to elucidate factors influencing the improvement in HRQL after smoking cessation therapy. In addition, the relationship between the nicotine addiction level and HRQL has not been elucidated to date. Although we made a diagnosis of nicotine dependence using the TDS test, this test was initially developed to screen for cases with nicotine dependence according to the DSM-III-R (Diagnostic and Statistical Manual of Mental Disorders), DSM-IV and ICD-10 (International Classification of Diseases).10 Thus, the TDS is regarded as a measure of the psychological and behavioural aspects of nicotine dependence.10 Such aspects of dependence may be important for prediction of changes in HRQL. Furthermore, nicotine dependence is a significant factor preventing smoking cessation. Ota et al22 reported high predictability of the TDS concerning smoking cessation among patients with coronary heart disease. Thus, our results encourage smokers, even if they are highly nicotine dependent and likely to quit smoking with difficulty, to participate in the smoking cessation programme to improve their health status.
When evaluating HRQL, both generic questionnaires and disease-specific questionnaires are available. Disease-specific questionnaires are likely to be more sensitive to particular symptoms and to slight responses to therapeutic interventions than are generic measures.23 Previous studies on the association between smoking cessation and HRQL used generic questionnaires such as the SF-36,6 ,8 ,9 ,18 ,20 the most popular generic instrument, EuroQOL6 or CDC HRQOL-4.17 In the present study, we used the SGRQ to measure HRQL in our cohort, which consisted of healthy smokers or smokers with various underlying diseases. The SGRQ, a respiratory-specific instrument, is especially designed to measure HRQL in patients with COPD.14 The reason we used the SGRQ was described in Methods section because our cohort consisted of smokers at risk of developing COPD or with early stages of COPD with a Brinkman Index ≥200. As we expected, previous studies using the SGRQ to measure HRQL in smoking cessation have been limited to those for patients with COPD. Tønnesen et al24 described changes in the SGRQ score in a smoking cessation study by nicotine replacement therapy for 370 smokers with COPD. A characteristic of their study is that the outcome of the smoking cessation therapy was divided into three groups: sustained abstainers, continuous smokers with no reduction and reducers. They found that reducers and sustained abstainers had both clinically and statistically significant improvements in all SGRQ scores and, with the exception of the activity score, improvements were greater in sustained abstainers than in reducers. No improvements in any of the SGRQ scores were shown in continuous smokers with no reduction. From these observations our results can be interpreted as follows. That is, most continuous smokers in our study might be considered as reducers as shown by the low exhaled CO levels at 12 weeks and the improvement in their SGRQ scores as well as those of quitters. Chen et al25 also reported changes in SGRQ scores by individual smoking cessation counselling for 85 smokers with COPD. They found that SGRQ scores were significantly improved in patients who abstained from smoking compared with those who failed to stop smoking. In that study, they did not mention the reduction in the number of cigarettes smoked or the exhaled CO level among patients with COPD who failed to stop smoking.
This study has some limitations. First, it was limited to one medical centre; therefore, the small sample size weakens the power of the study. Second, diagnoses of complications were self-reported and may underestimate the true population of participants with these complications. Third, we did not evaluate the follow-up HRQL in the dropout group, which might have biased the results. However, our study has highlighted the importance of completion of the smoking cessation treatment in improving HRQL regardless of quit status. An effort is needed to increase the completion rate of the smoking cessation programme in the future. Fourth, although we showed a short-term effect of smoking cessation therapy on improvements in HRQL, information on the long-term effects is not yet available. Continued improvement in HRQL with longer continuous abstinence has been confirmed.18 ,20 Therefore, long-term changes in HRQL, in particular in patients who failed to quit smoking, should be elucidated in the future. Finally, as we used a disease-specific HRQL measure, rather than a global measure designed to capture multiple important life domains such as the Quality of Life Inventory,26 our results should apply to only disease-specific HRQL.
In conclusion, HRQL of participants in the smoking cessation programme, being those who successfully quit as well as those who failed, improved significantly after the treatment. Baseline nicotine addiction level measured by the TDS was a predictor of that improvement. Further studies are needed to clarify the long-term effect of smoking cessation therapy on HRQL.