Smoking and Diabetes

This fact sheet examines the association between smoking and diabetes; including smoking as a risk factor for type 2 diabetes, how smoking can lead to multiple complications of diabetes and the benefits of stopping smoking among people with diabetes.

Diabetes mellitus is a metabolic condition which causes increased glucose levels in the blood.¹ Glucose is a sugar that the body produces primarily from the digestion of carbohydrates and levels are controlled by the hormone insulin. Insulin is made and stored in the pancreas and helps glucose to enter the cells where it is used as fuel by the body.¹ It can happen either when your body doesn’t produce enough insulin or the insulin you are producing, doesn’t work properly.²

There are several types of diabetes, but the main ones are two main types of diabetes:

Type 1 diabetes develops when your body cannot make insulin. This type most commonly affects children and young adults, and is a result of your body’s immune system attacking the cells that produce insulin in the pancreas. Less than 1 in 10 people with diabetes are Type 1 (8%).^{1 2 3}

Type 2 diabetes develops when your pancreas isn’t making enough insulin or your body can no longer react to the insulin it makes.^{1 2} Type 2 diabetes is much more common than Type 1 and tends to develop gradually as people get older – usually after the age of 40. But more and more people every year are being diagnosed at a much younger age. 9 in 10 people with diabetes are Type 2.^{1 2}

In the UK, that nearly 4.1 million adults have been diagnosed with diabetes, equivalent to just over 7% of the population. It has been estimated that around 850,000 people in the UK have undiagnosed Type 2 diabetes.^{4 5} Research compiled by Diabetes UK reports that diabetes is on the rise, with 5.3 million expected to be living with the condition by 2025.⁶ Research also show that people with type 2 diabetes are 50% more likely to die prematurely.^{5 7}

It is estimated that in the UK 7,827 deaths were caused by diabetes in 8 2020. Further analysis by British Heart Foundation reported that adults with diabetes are 2-3 times more likely to develop heart and circulatory diseases, and are nearly twice as likely to die from heart disease or stroke as those without diabetes.³

Cigarette smoking is one of the most important modifiable risk factor for type 2 diabetes.^{7 8} Evidence suggests that active and passive smoking are associated with significantly increased risks of type 2 diabetes.^{7 9} A study published in 2018 shows regular smokers have a 15-30% higher risk of developing diabetes, and that there is a clear dose-response relationship with the amount smoked and the earlier a person started smoking.^{10 11 12}

According to the Surgeon General’s Report, there are several ways in which smoking may increase a person’s risk for developing type 2 diabetes.^{8 9 13} The chemicals in cigarettes cause harm to your body’s cells and can interfere with their normal function.^{8 9 10} This can cause inflammation throughout the body, which may decrease the effectiveness of insulin.^{8 9} Additionally, when chemicals from cigarette smoke meet oxygen in the body, this process can also cause cell damage, called oxidative stress. Both oxidative stress and inflammation may be related to an increased risk of diabetes.^{8 9 10}

Smokers are also at greater risk of complications from diabetes.^{9 10} Research has demonstrated that the combined harmful effects of elevated blood glucose with cigarette smoking accelerates vascular damage in people with diabetes who smoke.^{7 9} Smoking can also make managing the condition and regulating insulin levels more difficult because high levels of nicotine can lessen the effectiveness of insulin, causing smokers to need more insulin to regulate blood sugar levels.^{7 10} Findings from a 2017 meta-analysis of observational studies demonstrate an adverse impact of smoking on the development of diabetic nephropathy in patients with Type 1 diabetes and Type 2 diabetes.¹⁴ Smoking is a documented risk factor for both the development and progression of various types of neuropathy (damage to the peripheral nervous system).^{15 16} A systematic review and meta-analysis published in 2015 found that smoking increased the risk of diabetic peripheral neuropathy by 42%¹⁷ and a prospective study found that cigarette smoking was associated with a twofold increase in risk.

The role of smoking as a potential risk factor for diabetic retinopathy (disorders of the retina) has been established in patients with type 1 DM^{18 19} but its role is disputed in patients with T2DM, with many studies reporting no association or even a decreased risk of developing retinopathy in smokers.^{20 21 22 23}

People with diabetes who smoke have an increased risk of premature death and an increased risk of heart disease in comparison to non-smokers with diabetes.^{12 14 25} A large body of evidences exists demonstrating that smokers have an increased risk of cardiovascular mortality, and a number of cardiovascular events including coronary heart disease, stroke and myocardial infarction, compared to non-smokers.¹⁶

Smoking is also associated with increased risk of cardiovascular complications.¹² A 2015 systematic review and meta-analysis involving nearly 6 million participants and over 295,000 new cases of type 2 diabetes found evidence of a 37% increase in risk among current smokers relative to non-smokers (relative risk 1.37, 95% CI 1.33–1.42).⁷ This effect was exposure related, relative risk ranged from 1.21 in light smokers up to 1.57 in heavy smokers.⁷

The risk of new-onset diabetes continues to increase in the first few years after smoking cessation compared to never smokers and then begins to decline, and the risk becomes comparable to those who never smoked.⁷ Findings from meta-analysis which included 10 prospective studies (1,086,608 participants) demonstrated that when comparing never smokers with quitters, the risk of diabetes was increased, with a relative risk = 1.54 (95% CI: 1.36–1.74) for those who had quit smoking less than 5 years before baseline, relative risk decreased progressively for those who stopped for 5–9 years to a RR of 1.18 and to a RR of 1.11 for those abstaining for ≥ 10 years.⁷ These findings were in agreement with a recent 2019 meta-analysis based on data from 5 077 289 participants and 223 084 incident cases of type 2 diabetes, research findings confirmed that cigarette smoking was an important risk factor for type 2 diabetes.²⁶ Compared with non-smokers, the risk for type 2 diabetes increased by 35% for current male smokers and 27% for current female smokers, respectively.^{17 26}

Research has consistently and unequivocally demonstrated that quitting smoking could be one of the most important health decisions you ever make, irrespective whether you have diabetes or not. As well as being an independent diabetes risk factor, for people who already have diabetes smoking increases complication risk. Smoking cessation advice should be a routine component of the diabetic care team diabetic care. NICE reported that 90.2% of people with type 1 diabetes and 95.5% of people with type 2 diabetes had their smoking status checked within the last year.^{26 27}

Many diabetics do not stop because of concerns over weight gain. Research has shown that smoking cessation that was accompanied by substantial weight gain was associated with an increased short-term risk of type 2 diabetes but did not mitigate the benefits of quitting smoking on reducing cardiovascular and all-cause mortality.^{28 26 27} Further research is required to develop interventions which prevent excessive weight gain in order to maximize the health benefits of smoking cessation through reducing the short-term risk of diabetes and further lowering the long-term risk of death.^{29, 30} Concerns about weight gain should be addressed by health care providers addressing and supporting people’s concerns around weight gain and giving strategies to help prevent it. Whilst also emphasising the health benefits of smoking cessation.^{26 27 31}

It is particularly important for those who have other risk factors such as high blood pressure, raised blood cholesterol levels, diabetes, obesity, or are physically inactive to quit smoking. Smokers who wish to reduce their risk of CVD should be informed: 1) that the only reliable way of doing so is stopping smoking completely and 2) that smoking reduction alone is unlikely to reduce their risk significantly. However, if they are unable to stop smoking, they may wish to attempt smoking reduction with the help of NRT or an e-cigarette, but that their ultimate goal should be to fully quit smoking in the near future when they feel they are able to do so.

For further information on quitting smoking see:

• ASH. Stopping smoking. March 2020
• NHS advice and support on quitting

Emma Elvin, Senior Clinical Advisor, Diabetes UK.
Diabetes UK Statistics Team.