factsheet no:23

Smoking and diabetes

Action on Smoking and Health – November 2002

What is diabetes?

Diabetes occurs when the glucose level in the blood is too high because the body cannot use it properly.  Glucose is a sugar that the body makes mainly from the carbohydrates in food.  Glucose comes from the digestion of starchy foods such as bread, potatoes, chapatis, from sugar and other sweet foods and from the liver which makes glucose   Glucose levels are controlled by the hormone insulin which is made and stored in the pancreas.  Insulin helps glucose to enter the cells where it is used as fuel by the body and consequently  the amount of glucose left in the bloodstream goes down.

Types of Diabetes

There are two types of diabetes:  People with Type 1 diabetes (insulin-dependent) do not produce any insulin.  People with Type 2 (non-insulin dependent) diabetes do not produce enough insulin, or the insulin that the body does produce doesn’t work properly.

Type 1 diabetes is the less common form.  This type usually develops in children and young adults but can occur at any age.  It is thought that Type 1 diabetes occurs when the body’s immune system destroys the cells that produce insulin but it’s not known what causes this to happen.

About 90% of people with diabetes have Type 2 diabetes.  This condition tends to develop gradually after the age of 40.  However, increasingly,  Type 2 diabetes is being diagnosed in younger people, including children.  It appears that this is largely due to the fact that individuals have less active lifestyles and an increasing number are overweight.   Both genetic and environmental factors contribute to the development of diabetes but  the development of Type 2 diabetes is more likely if some or all of the following factors are also present:  physical inactivity; being overweight; family history of Type 2 diabetes; previous diabetes in pregnancy. The condition is also more common in people of Asian and African-Caribbean origin. [1]

Prevalence of diabetes

In the UK, there are about 1.4 million people diagnosed with diabetes and a further 1 million are believed to be undiagnosed.  It is estimated that there will be up to 3 million people with diabetes by 2010.  There are about 33,000 deaths in the UK attributable to diabetes – about 1 in 7 of all deaths.  At least half of these deaths are from cardiovascular disease. [2]

Health consequences

People with  diabetes are at greater risk of raised blood pressure, heart disease, stroke, kidney disease, nerve damage and eye complications such as retinothapy (disorders of the retina). [3]  

Links between smoking and diabetes

There is a growing body of evidence to suggest that smoking is an independent risk factor for diabetes and that among people with diabetes, smoking aggravates the risk of serious disease and premature death.

In the US Nurses’ Health Study, 114,247 women were followed for 8 years and 2,333 cases of type 2 diabetes were confirmed.  After controlling for multiple risk factors,  the relative risk of diabetes was 1.42 among women who smoked 25 or more cigarettes a day compared with non-smokers, suggesting a moderate association between smoking and the subsequent development of diabetes. [4]

A similar study of 41,810 middle aged men found that those who smoked more than 25 cigarettes daily had a relative risk of diabetes of 1.94 compared with non-smokers. [5]  

A prospective study of Japanese men concluded that age of smoking initiation and number of cigarettes smoked were major risk factors for developing diabetes. [6]    Similarly, data from the US Cancer Prevention Study 1 found that as smoking increased so the rate of diabetes increased for both men and women. [7]

People with diabetes already have an increased risk of heart disease, which is further elevated if they smoke.  Diabetes acts in several ways to damage the heart: high glucose levels affect the walls of the arteries making them more likely to develop fatty deposits which in turn makes it more difficult for the blood to circulate. People with diabetes are more likely to have high blood pressure and high levels of fats such as triglycerides.  They are also more likely to have lower levels of the protective HDL cholesterol^. 1

Insulin Resistance

Smoking has also been identified as a risk factor for insulin resistance which can lead to diabetes.  People with insulin resistance cannot properly use insulin and such people may initially have higher than normal amounts of insulin circulating in their blood, a condition known as hyperinsulinemia. 

Several factors, including genetics and obesity, increase a person’s risk of insulin resistance and smoking has also been shown to increase the risk of this condition.  It is believed that catecholamines, a type of hormone, are produced in greater quantity in smokers and act as an antagonist to insulin action. 3   A study of 40 patients with Type 2 diabetes found insulin resistance was markedly aggravated among those who smoked. [8]    

Smoking, diabetes and premature death

The elevated risk of heart disease among people with diabetes increases the risk of premature death.  In one study of women aged 60 to 79 who smoked and developed Type 2 diabetes, an estimated 65 per cent of the cardiovascular disease deaths among the subjects was attributed to the interaction of cigarette smoking and diabetes. [9]  The same study suggested that smoking may trigger fatal events in people with diabetes whose circulation has been compromised due to vascular disease, or blood vessels damaged by a combination of smoking and diabetes.  A large prospective study of US nurses found that among those with diabetes the relative risks of mortality were 1.31 for past smokers, 1.43 for current smokers of 1-14 cigarettes per day, 1.64 for smokers of 15-34 cigarettes per day, and 2.19 for current smokers of 35 or more cigarettes per day. [10] 

The effect of smoking on complications of diabetes

Smoking is associated with multiple complications of diabetes.  Nephropathy (kidney disease) has been shown to be common in Type 1 diabetic patients who smoke [11]  and smoking increases the risk of albuminuria in both types of diabetes. [12] [13] (Albuminuria refers to the presence of protein  in the urine and can indicate signs of kidney disease.)  Another small study of 33 people with type 2 diabetes with kidney disease found that smokers’ kidney function declined more rapidly than that of non-smokers, despite drug treatment, suggesting that smoking cessation could slow the progression of kidney disease in people with diabetes who use ACE inhibitors. [14]

The relationship between cigarette smoking and retinothapy (disorders of the retina) is less well defined than that of other microvascular complications of diabetes.[15]  However, some studies have found an association between smoking and diabetic retinopathy. [16]  11

Smoking is also a documented risk factor for both the development and progression of various types of neuropathy (damage to the peripheral nervous system).  A retrospective case control study of type 1 and type 2 diabetic patients found that current or ex-smokers were significantly more likely to have neuropathy than individuals who never smoked (64.8% vs. 42.8%).[17]  A more recent prospective study found that cigarette smoking was associated with a 2-fold increase in risk.[18]   

Benefits of smoking cessation

There is overwhelming evidence that stopping smoking reduces the risk of cardiovascular disease, lung disease, cancer and stroke. [19]  (See also ASH Fact sheet 11: What happens when you give up smoking.)   As diabetes increases the risk for heart disease and stroke, it follows that stopping smoking will reduce the risk of complications from diabetes such as heart disease.   Few studies have evaluated smoking cessation treatment specifically for people with diabetes but the limited research available suggests that smokers with diabetes may be less successful in quitting than smokers without diabetes and that intensive strategies should be considered to optimise successful cessation. 15

One possible explanation for the lower quitting rates among people with diabetes is the fact that stopping smoking is associated with weight gain and this is likely to be of concern in people who have diabetes and are already overweight.  One US study found that concerns about weight gain among smokers with Type 1 diabetes were particularly prevalent among women, obese smokers, and those in poor metabolic control. [20]  Fear of weight gain was cited by 49% of smokers.

A recent British prospective study of 7,735 men aged 40-59 years found that cigarette smoking was associated with a significant increase in risk of diabetes, even after adjustment for age, body mass index, and other potential confounding factors.  The benefit of giving up smoking was only apparent after  5 years of smoking cessation and risk reverted to that of never-smokers only after 20 years.  Men who gave up smoking during the first 5 years of follow-up showed significant weight gain and subsequently higher risk of diabetes than continuing smokers.  However, the authors concluded that in the long term, the benefits of giving up smoking outweigh the adverse effects of early weight gain. [21]

Stopping smoking also reduces the risk of premature death.  The US Nurses’ Study found that among women with Type 2 diabetes who had stopped smoking for 10 or more years had a mortality relative risk of 1.11 compared with diabetic women who were never smokers.10

In the light of the growing evidence demonstrating that smoking is an independent risk factor for diabetes and that it is also an aggravating factor for diabetes complications, smoking cessation advice should be a routine component of diabetic care.  Concerns about weight gain should be addressed by health care providers whilst emphasising the fact that the health benefits of smoking cessation far outweigh post cessation weight gain, even in people who are focused on weight management.