Smoking and diabetes

King James 1st of England announced: ‘this Tobacco, is not simply of a dry and hot qualitie; but rather hath a certaine venemous facultie joyned with the heate thereof, which makes it have an Antipathie against nature, as by the hatefull smell thereof doeth well appeare.’ He considered smoking ‘A custome lothsome to the eye, hatefull to the Nose, harmefull to the braine, dangerous to the Lungs.’1 Doll and Peto's landmark study of 34 439 male British doctors is well-known – their 50-year analysis concluded: ‘A substantial progressive decrease in the mortality rates among non-smokers over the past half century (due to prevention and improved treatment of disease) has been wholly outweighed, among cigarette smokers, by a progressive increase in the smoker v non-smoker death rate ratio due to earlier and more intensive use of cigarettes.’ ‘On average, cigarette smokers die about 10 years younger than non-smokers. Stopping at age 60, 50, 40, or 30 gains, respectively, about 3, 6, 9, or 10 years of life expectancy.’2 The Surgeon General reached this conclusion after a meta-analysis of 46 studies including over 3.9 million people among whom 140 813 had diabetes. Analyses were controlled for age, sex, ethnicity, BMI, waist circumference/waist-hip ratio, diet, physical activity, alcohol intake, family history of diabetes, education, fasting glucose, insulin, and lipid profile. The relative risk of new diabetes in people who smoked was 1.37 (95% CI 1.31–1.44). Even when the largest studies were excluded, or potential publication bias was corrected, smokers had a significantly increased risk of newly-diagnosed diabetes. Compared with people who had never smoked, the relative risk among former smokers was 1.14 (1.09–1.19); light smokers 1.25 (1.14–1.37), and heavy smokers 1.54 (1.40–1.68).3 A meta-analysis of 88 studies in 2015 including 5 853 952 participants found a relative risk of new type 2 diabetes of 1.37 (1.33–1.42) among current smokers compared with non-smokers. Stopping smoking reduced the relative risk of diabetes to 1.14 (1.10–1.18) compared with never-smokers. Passive smoking increases the risk of diabetes too – never smokers exposed to passive smoke had a relative risk of 1.22 (1.10–1.35) compared with those not exposed. The authors state: ‘Based on the assumption that the association between smoking and diabetes risk is causal, we estimated that 11.7% of cases of type 2 diabetes in men and 2.4% in women (ie, about 27.8 million cases in total worldwide) were attributable to active smoking.’ Twenty-seven million! Stopping smoking reduces the risk of developing diabetes. In one study, when compared with people who never smoked, smokers who stopped less than five years ago had a relative risk of 1.54 (95% CI 1.36–1.74), while those who stopped 10 or more years ago had a relative risk of 1.11 (1.02–1.20).4 Smokers who quit should avoid substantial weight gain. Analysis of three cohort studies found that the risk of developing type 2 diabetes increased during two to six years after stopping (hazard ratio 1.22; 1.12–1.32) compared with current smokers. Thereafter the risk gradually fell. This temporary increase in risk was proportional to weight gain and was not seen in those who did not gain weight. However, regardless of weight gain, after smoking cessation, cardiovascular and all-cause mortality fell.5 Discuss this with patients – various diabetes forums emphasise the increased risk of dia-betes after smoking cessation. Smoking kills, whether one has diabetes or not. Having diabetes confers an increased risk of cardiovascular disease. Smoking exacerbates this. A meta-analysis including a total of 89 cohort studies concluded that, among those with diabetes, ‘The pooled adjusted relative risk associated with smoking was 1.55 (1.46–1.64) for total mortality (48 studies with 1 132 700 participants and 109 966 deaths), and 1.49 (1.29–1.71) for cardiovascular mortality (13 studies with 37 550 participants and 3163 deaths).’ Stopping smoking reduces this risk: ‘In comparison with never smokers, former smokers were at a moderately elevated risk of total mortality (1.19; 1.11–1.28), cardiovascular mortality (1.15; 1.00–1.32), cardiovasc-ular disease (1.09; 1.05–1.13), and coronary heart disease (1.14; 1.00–1.30), but not for stroke (1.04; 0.87–1.23).’6 In the ADVANCE study, those men and women who stopped smoking had a 30% reduction in all-cause mortality.7 Smoking is linked with the development, progression, and poor healing of diabetic foot disease.8 In a meta-analysis, smokers were more likely to have a diabetic foot amputation (major or minor) than non-smokers (odds ratio 1.65; 1.09–2.50).9 Smoking (presumably via nicotine) decreases retinal blood flow in addition to its wider effect of reducing the oxygen-carrying capability of the blood via increased carboxyhaemoglobin. Hypoxia increases the risk of progression of diabetic retinopathy.10 So smokers would seem more likely to have diabetic retinopathy than non-smokers. Studies of the effect of smoking on retinopathy give variable results. A recent meta-analysis concluded that, in type 1 diabetes, smoking increased the risk of both diabetic retino-pathy in general, and of proliferative retinopathy in particular, when compared with non-smokers. Surprisingly, overall, smokers with type 2 diabetes had less retinopathy than non-smokers.11 A meta-analysis compared people with nephropathy, with and without diabetes. The odds risk of smoking among those with diabetic nephropathy was 1.70 (1.48–1.95), compared with those with non- diabetic nephropathy.12 ‘There's nothing like that first heady pull – preferably, if you ask me, on a fire escape in winter, with a good mate and a mug of whiskey. There's also the supreme pleasure derived from doing something so despised by a vast array of people… Where there's a “No Smoking” sign, you can bet I'm somewhere close at hand… And look, I know all about the warning label affixed to every pack of Marlboro Reds I buy. I know – and believe – what the surgeon general says… In short: I get it, smoking kills. And I fully intend to quit. Just … not yet.’13 ‘I found stopping smoking one of the most difficult things I ever faced in life… I am so glad I did stop because with the numerous health problems I have now I doubt I'd be coping very well at all with it all… As it is I've more or less turned the T2 around and I doubt I could have done that whilst gasping and wheezing.’14 NICE supports the following evidence-based interventions to help adults stop smoking: behavioural support (individual and group); bupropion, nicotine replacement therapy; short- and long-acting varenicline; very brief advice.15 It is obviously best not to use nicotine products at all. However, many people find giving up smoking impossible. E-cigarettes are regarded as about 95% safer than traditional cigarettes16 but, although they do not contain tar, they still contain nicotine, delivery compounds, and flavourings. They have not been in wide use for long enough for evaluation among people with diabetes, but it is unlikely that people with dia-betes differ from those without diabetes in their response to e-cigarettes. A systematic review did not find evidence of efficacy of intensive interventions for smoking cessation among people with diabetes.17 However, a recent study in people with diabetes compared the intensive Ottawa Model for Smoking Cessation programme (OMSC), delivered by specially-trained diabetes educators, with people given usual advice. ‘Smokers in the OMSC group received counseling, a discount card to partially cover the cost of smoking cessation medication, and follow-up telephone calls over a 6-month period.’ Biochemically confirmed smoking cessation at six months in those on the OMSC was 11.1% compared with 2.6% in the control group (odds ratio 3.73; 1.20, 11.58).18 Stopping smoking may affect blood glucose balance which should be monitored to allow diabetes treatment adjustment. I thank Professor John Britton for reminding me of the importance of this topic and for introducing me to some of the recent literature.

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