Characteristics of Smoking Quitters in Type 1 and Type 2 Diabetes: A Five-Year Cohort Study

Lipid levels


Smoker
(n= 1641)


Quitter
(n=468)


Total
(n=2109)


p*




On statin therapy in 2009


87.6% (1437)


85.5% (400)


87.1%
(1837)


0.23 NS




On statin therapy in 2014


78.2% (1284)


82.3% (385)


79.1%
(1669)


0.06 NS




Decrease in total-cholesterol 2009 to 2014 (mean ± SD)


0.17±1.07


0.36±1.13


0.21±1.09


<0.01




Decrease in triglyceride 2009 to 2014 (mean ± SD)


0.37±1.62


0.37±1.99


0.37±1.71


0.96 NS




Increase in HDL-cholesterol 2009 to 2014 (mean ± SD)


0.09±0.31


0.04±0.35


0.78±0.32


<0.01

Table 5: Type 2 diabetes patients on statin therapy plus total-cholesterol,
triglyceride and HDL-cholesterol levels in smokers and quitters at the beginning
and the end of the five-year follow-up.

Mortality and survival

16.5% of the patients with type 2 diabetes died between 2009 and 2014 (1762/10664). Mortality was slightly higher among smokers (18%, 296/1641) compared to those who quit (16%, 75/468) but the difference was not significant (p=0.31, chi-square test). Survival from diagnosis was best for non or ex-smokers at the start of the study (median survival 10,053 days) followed by those who quit smoking between 2009 & 2014 (median 9199 days) and worst for those who continued to smoke (median survival 7948 days) The differences were significant (p=0.01).

Discussion

In this observational study we found that the prevalence of smoking was higher in type 1 diabetes than in type 2 diabetes. This probably reflects the age difference between the two diabetes groups and reflects the prevalence by age seen in the general population [20]. Smoking prevalence was associated with deprivation in both type 1 and type 2 diabetes again reflecting the general population [21]. Previously we have shown that the prevalence of type 1 diabetes is not associated with socioeconomic status, but the prevalence of type 2 diabetes is clearly associated with deprivation [22].

In this observational study in type 2 diabetes, we found that just over 20% of smokers with type 2 diabetes quit smoking between 2009 and 2014, which is similar to other studies [16]. Smokers were slightly younger but there was no significant difference in age between smokers and quitters. Our study confirmed the clear relationship between smoking and social deprivation [23]. Despite starting from a lower baseline, a greater percentage of smokers with type 2 diabetes in the least deprived quintile quit smoking during the study period although this did not achieve statistical significance. Previous literature suggests potential explanations for the link between smoking cessation behaviours and poverty. Individuals of a lower income and education are less knowledgeable of the hazards of smoking, the benefits of smoking cessation aids and smoking cessation programs [16,23-26]. Interestingly, in the USA it has been reported that tobacco use declined between 1999 and 2010 in people without diabetes but not with diabetes [27]. Cost is a potential barrier to accessing smoking cessation medications and lower-income groups utilize smoking cessation aids less frequently than higher-income groups. For the economically disadvantaged, there is more financial stress and less respite from life’s demands. The preoccupation with meeting the needs of daily living may discourage taking on the additional demands of quitting smoking [24,25]. Furthermore, when smokers from poorer socioeconomic groups do try to quit, they are less likely to be successful than other smokers [24-26].

We demonstrated that there was a clear relationship between the prevalence of smoking and duration of type 2 diabetes, which probably reflects increased mortality risk with duration. Quitting may also reflect patient concern about mortality risk with increasing duration of diabetes. There was no difference in the mean ages between the groups therefore age was not a factor [21].

The change in glycaemic control with quitting smoking is of interest because patients often believe that smoking cessation will lead to a large and significant deterioration in glycaemic control. In type 1 diabetes there was no significant change while in type 2 diabetes there was a small (0.1%; 2.13 mmo/mol) increase in HbA_1c. More smokers improved their BMI while more quitters increased their BMI to greater than 30kg/m². Previous studies have suggested that the overall mortality risk benefit of stopping smoking outweighed the mortality risks of weight gain and poorer glycaemic control [29]. Presumably some of the benefit of quitting smoking in type 2 diabetes is secondary to the reduction of the adverse effects of smoking on the action of insulin and function of pancreatic β-cells [4]. There needs to be greater understanding that the potential weight gain and minimal deterioration in glycaemic control, particularly in type 2 diabetes, is associated with less morbidity and mortality than continued smoking [25,29]. Unfortunately, we did not have information on individual weight changes.

In our study there was evidence to suggest that smokers with type 2 diabetes in the five-year follow-up period had a higher mortality risk, and that quitting smoking reduced mortality. Recently published data from the Framingham Heart Study indicated that among heavy smokers in a non-diabetic population, smoking cessation was associated with a significantly lower risk of cardiovascular disease within five years relative to current smokers [28].

Our study demonstrated that the presence of IHD was associated with an increased level of stopping smoking. There was no association between quitting smoking and hypertension, retinopathy, neuropathy or foot ulcers. The level of quitting with IHD may reflect peoples’ greater awareness of the association of IHD with smoking, particularly in patients with diabetes. It may also reflect targeted smoking cessation in this group such as cardiac rehabilitation classes.

The changes in the patients taking statin therapy and the changes in lipid levels are more difficult to explain. The increased number of smokers stopping their statin therapy may reflect their reduced concern about their general well-being and health including their diabetes [11]. The decrease in the total-cholesterol in the quitters may reflect the greater number staying on statin therapy plus possible changes in diet. The small but significant increase in HDL-cholesterol is much more difficult to explain.

There are several possible limitations in our observational study. The motivations behind patients quitting smoking were unknown, as were the length of time which people had quit smoking for within the 5-year period examined, the smoking relapse rate and how patient gender affected quitting smoking. In addition, data was self-reported by patients and does not specify the amount of tobacco smoked. However, we can be certain that the data that we collected from the General Practice databases were accurate, as it was based on Quality Outcome Framework data [17].

Smoking cessation is a process initiated by the intention to quit. Intention to quit is affected by individual (perceived susceptibility and benefits, severity of harms), social (social group norms, cultural acceptability), and environmental factors (barriers and accessibility to support) [23,29-30]. Using data from retrospective reports of ex-smokers, health reasons, including both smoking related symptoms (present health) and the desire to avoid future illness (future health), were by far the most frequently mentioned motives reported by the successful quitters, followed by social reasons and, less frequently, economic cost [28,29-30]. Tobacco dependency often requires multiple quit attempts and patients may relapse after several years of cessation [23,29-30].

There is a great deal of work that needs to be undertaken to reduce the prevalence of smoking in Scotland and the UK to the lower levels seen in other parts of western Europe. There needs to be a greater knowledge and understanding in the non-diabetes and diabetes populations of the deleterious effects of smoking on health. In addition, there needs to be a greater understanding that the possible weight gain in both groups and the deterioration in glycaemic control observed in type 2 diabetes is associated with less morbidity and mortality risk than continued smoking [28]. People with diabetes are faced with the challenge of making extensive changes to their lifestyle, a burden that may be increased by attempts to stop smoking. Tailoring smoking cessation programmes to the needs of people with diabetes may lead to improved outcomes, compared with the usual care, but possibly increases the burden of self-management.

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