Study results revealed a significant effect of the intervention throughout the study period among all participants with respect to the number of cigarettes smoked per day, however this effect was not significant but obvious in terms of blood pressure. Furthermore, differences between participants in the control and intervention groups in terms of the cigarettes smoked per day can be considered one of the main findings of this stud. Despite randomisation of subjects into the groups, patients in the control group smoked less number of cigarettes and had lower CO level than those in the intervention group (Table 1). However, patients in the intervention group demonstrated improvements in these terms. Furthermore, we observed a clear decrease in the mean number of cigarettes smoked per day between the baseline and third visits as well as a significant difference between the two groups for first and second visits, and these results were confirmed by the multivariate longitudinal analyses. These results can direct future research in this setting. The decrease in the number of cigarettes smoked can enhance future quitting attempts and the success rate (35). Previous studies have reported conflicting results. For instance, a study conducted in Indonesia had reported a non-significant difference between the patient groups with respect to the number of cigarettes smoked (18). However, a study by Canga et al. (14) had demonstrated similar results with the current study in which the mean number of cigarettes between both groups showed significant differences in favour of the intervention group after 6 months (14).
We assume that smoking cessation is a major determinant of glycaemic control, in addition to other measures for diabetes management. Participants’ glucose control did not differ over the study period within or between the groups. It is possible that the duration of the study follow-up was insufficient to reveal a clear difference in glycaemic control. In addition, this study relies on a brief cognitive behavioural therapy (CBT) only rather than combination of CBT and pharmacotherapy which has been shown to give better abstinence rate. Therefore, the present study utilized low-intensity intervention strategy witho only 5-minute brief smoking cessation advice delivered by the physician. However, a study by Hokanson and colleagues in 2006 revealed an improvement in the HbA1c level over the study period that may have been related to the long study period of approximately three years (17). Another study in France reported a significant decrease in the glycated haemoglobin level (16). Furthermore, participants’ BP significantly improved over the study period, as confirmed by the repeated measures effects. As BP can exhibit changes faster than any other measure and many studies showed that sudden quitting can lead to an increment in the BP rather than decrement (36–39), however this study participants reduced the number of cigarette smoked rather than cut it down that aligned with BP improvement (40). The lack of differences between the two groups may relate to random patients’ selection and not according to their willingness to stop tobacco smoking based on the transtheoretical model’s stage of change. The Hokanson study yielded different results, as there were no differences in BP between the participants over the study period (17).
One limitation of the present study was the use of Smokerlyzer piCO + to measure the CO level for verification of tobacco cessation. This tool cannot be considered as accurate as urine cotinine, because patients can inhale environmental CO from other sources that may tend to give false-positive results. The patients’ CO levels decreased over the study period, consistent with the decrease in the number of cigarettes smoked; however, these results were not significant based on inferential analyses. The higher CO level in the intervention group compared with the control group comes consistent with the higher number of cigarettes smoked by them. A significant proportion of patients exhibited a reduction in the number of cigarettes smoked, but the number of patients who succeeded in quitting was small. Furthermore, there was no difference in the quitting rate between the two groups, which may be the result of the short study period (6 months only), absence of NRT to boost the intervention effect and random selection of patients in the two groups not according to their willingness to quit smoking. A randomised controlled trial in Spain reported opposite findings in the difference in the quitting rate between the two groups; the rate of quitting cessation was 7.5-fold higher in the intervention group than the control group (14). Another randomised controlled trial in Canada showed no differences between the intervention and control groups after 6 months, although there was a difference at the 3-month time point (17).
No significant differences were observed neither between patients in the two groups with respect to their lipid profile (TG, and LDL, HDL, and total cholesterol) and nor in their repeated measures over the study period. Although patients in the two groups exhibited improved total cholesterol after the study, the improvement was insignificant. To improve and identify differences in patients’ lipid profiles, long-term studies would be required.