Double diabetes is a term that may be used to describe the development of insulin resistance in someone with type 1 diabetes.

Insulin resistance is a state in which the body’s cells develop difficulty using the hormone insulin to process glucose (blood sugar) for energy. It is a hallmark of type 2 diabetes but can also develop in some people with type 1 diabetes, especially those who become overweight or obese.

The most significant risk factor for double diabetes is obesity. A physician may suspect double diabetes in patients with type 1 diabetes who develop signs and symptoms of insulin resistance and type 2 diabetes. In some cases, the patient may have originally been diagnosed with type 2 diabetes. To establish a diagnosis, several laboratory tests may be conducted, including autoantibody testing and the C peptide test.

People with double diabetes may be more prone to certain complications, such as heart conditions. However, having double diabetes does not mean a patient will develop more problems, according to the National Diabetes Education Program.

Double diabetes is treated with medication, exercise, diet and weight loss. People can help prevent double diabetes by maintaining a healthy body weight, adhering to a healthful diet regimen, being physically active and getting regular medical care.

Double diabetes is a nonscientific term used to describe the development of insulin resistance (a hallmark of type 2 diabetes) in people with type 1 diabetes. It is a recent phenomenon and has been linked to the growing epidemic of obesity, particularly childhood obesity.

Although type 1 and type 2 diabetes share many of the same characteristics, they are different diseases. Type 1 diabetes is an autoimmune disease in which the body mistakenly attacks the insulin-producing cells of the pancreas. Insulin is a hormone needed to process glucose (blood sugar) for energy. Poorly controlled glucose damages the blood vessels, nerves and other structures. Patients with type 1 diabetes must administer insulin regularly. This disease is usually diagnosed in childhood.

Type 2 diabetes is a metabolic disorder. Generally, the body keeps making insulin but has trouble using it. Obesity is typically a factor in this insulin resistance. In addition, the pancreas’ production of insulin may decline. Some patients control type 2 diabetes through exercise and diet, but many also require oral or injectable antidiabetic agents and/or insulin.

In some cases, people with type 1 diabetes go on to develop insulin resistance, typically as a result of obesity. Excess fat makes it harder for the body to use insulin. Because they are unable to process the insulin they take by injection or other means, people with double diabetes often require higher doses of insulin to control their glucose.

Heredity is another risk factor for double diabetes. Research has found an increased chance of developing double diabetes in type 1 patients who have inherited certain genes associated with insulin resistance and type 2 diabetes.

Because patients with double diabetes may have signs and symptoms of type 1 and type 2 diabetes, diagnosis and treatment may be difficult. Additionally, insulin resistance and a related condition called hyperinsulinemia (excess insulin in the bloodstream) are associated with numerous health problems, including:

• Atherosclerosis
• High blood pressure
• Unhealthy levels of cholesterol

• Heart conditions
• Obesity
• Metabolic syndrome
• Fatty liver
• Increased risk of certain cancers
• A skin condition called acanthosis nigricans
• Polycystic ovarian syndrome, a hormonal problem that can affect women

The many potential complications of diabetes include cardiovascular disease, kidney disease (diabetic nephropathy), nerve disease (diabetic neuropathy) and eye diseases such as diabetic retinopathy and glaucoma. Some research has suggested that people with double diabetes may be at greater risk for problems such as coronary artery disease. However, having double diabetes does not mean a person will develop more complications, according to the National Diabetes Education Program.

Some research has found that 10 percent or more of diabetic children may have double diabetes. Major research projects, including the multicenter SEARCH for Diabetes in Youth study, are trying to establish reliable statistics on the incidence of the various forms of diabetes.

Double diabetes is sometimes called hybrid diabetes, mixed diabetes, type 1.5 diabetes or type 3 diabetes. However, the term “type 3 diabetes” has been used also to describe other conditions, including gestational diabetes and Alzheimer’s disease, which according to one theory involves insulin resistance in the brain. The term “type 1.5 diabetes” has been used also to refer to two disorders that do not involve insulin resistance or obesity:

• Latent autoimmune diabetes in adults (LADA). A variation of type 1 diabetes that can develop in adulthood.
  
  
• Maturity-onset diabetes of the young (MODY). A rare genetic form of diabetes that is sometimes considered a form of type 2 diabetes and is sometimes misdiagnosed as type 1.

There are a number of factors that may cause double diabetes. The most significant cause of insulin resistance in a patient with type 1 diabetes is obesity because extra fat in the body impairs the effectiveness of insulin.

A healthy weight range can be determined by a person’s body mass index (BMI) or waist-hip ratio. A person with a BMI of 25 to 29.9 is considered overweight. A person with a BMI of 30 or more is considered obese. The distribution of weight is also a factor. People with excess weight above their hips, especially around their abdomen (central obesity), are at a higher risk than those with excess weight on their hips and thighs. For more information, see Obesity & Diabetes.

Excess weight also increases the risk of many other conditions including high blood pressure, unhealthy cholesterol levels, heart conditions, stroke, certain cancers, sleep apnea and sexual dysfunction.

The risk of developing insulin resistance generally increases with age, but many of the reported cases of double diabetes have occurred in adolescents and young adults. This is believed to be due to a combination of increased incidence of type 1 diabetes and the growing epidemic of childhood obesity.

Recent research shows that the proportion of patients who were overweight when diagnosed with type 1 diabetes tripled from the 1980s to the 1990s. Scientists also found that overweight children developed type 1 diabetes at an earlier age, possibly because insulin resistance hastened the loss of insulin-producing beta cells.

Other risk factors for double diabetes include a family history of type 2 diabetes and the inheritance of certain genes linked to insulin resistance. Race may also play a role. Some research has found double diabetes to be more common in black children than in white children, though whites are at greater risk for type 1 diabetes.

The symptoms of double diabetes may vary. Physicians may suspect double diabetes in a patient with type 1 diabetes who begins to exhibit signs and symptoms of insulin resistance and type 2 diabetes.

Possible indicators that someone with type 1 diabetes may have developed or be developing double diabetes include:

• Acanthosis nigricans (dark patches in skin folds)
  
  
• Weight gain and central obesity
  
  
• Decreased effectiveness of insulin therapy or need for rising dosages
  
  
• Chronic hyperinsulinemia
  
  
• Evidence of metabolic syndrome, such as increased blood pressure and unhealthy levels of cholesterol and triglycerides
  

  

• Presence of genes linked to insulin resistance
  
  
• Polycystic ovarian syndrome in females

In some cases, a child with double diabetes may have originally been diagnosed with type 2 diabetes but actually have type 1 and insulin resistance. Distinguishing among the various types of diabetes can be difficult. The signs and symptoms of type 1 diabetes generally develop rapidly, over several weeks or months. They can include:

• Extreme thirst (polydipsia)
• Excessive urination (polyuria)
• Increased appetite (polyphagia)
• Fatigue
• Vision changes
• Unexplained weight loss
• Sweet, fruity-smelling breath

The signs and symptoms of insulin resistance, prediabetes and type 2 diabetes usually develop over a longer period of time and may go undiagnosed for years. Some of these symptoms are similar to those of type 1 diabetes. Additional symptoms may include:

• Numbness or tingling in hands or feet
• Dry, itchy skin (pruritus)
• Slow-healing sores
• Frequent infections
• Red, swollen or tender gums

There is no scientific or clinical definition of double diabetes, nor any gold standard for diagnosis. This may make diagnosis challenging. Physicians may suspect double diabetes if the patient has been diagnosed with type 1 diabetes and begins to show signs and symptoms of insulin resistance and type 2 diabetes, particularly obesity and acanthosis nigricans.

A physician suspecting double diabetes will typically begin by reviewing the patient’s medical history and performing a physical examination. Several laboratory tests may be conducted, such as:

• C-peptide test. This blood test can indicate hyperinsulinemia (excess insulin in the blood) and help distinguish type 2 diabetes from type 1.
  
  
• Autoantibody test. Antibodies are proteins released by the immune system that attack a perceived threat. The islet cell antibodies associated with type 1 diabetes are generally lacking in patients with type 2 diabetes. Patients who display the signs and symptoms of type 2 diabetes yet have these antibodies may have double diabetes.
  
  
• Glycohemoglobin test. The standard measure of long-term control of glucose (blood sugar), this blood test can suggest whether the effectiveness of a patient’s insulin therapy is declining, which could be due to insulin resistance.
  
  
• Genetic tests. These may reveal if a patient with type 1 diabetes has certain genes that have been linked to insulin resistance and type 2 diabetes. Scientists have found increasing numbers of such genes in recent years.
  
  
• Ketone test. This measures the amount of ketones, an acidic waste product, in a person’s urine or bloodstream. An excessive level of ketones (ketosis) is more common in people with type 1 diabetes.

A physician is likely to take a blood pressure reading and order a cholesterol test to see if an overweight patient has or is at risk for metabolic syndrome, which is associated with insulin resistance and double diabetes.

The goal for most patients with double diabetes is to lose weight while controlling their type 1 diabetes. The physician will recommend a healthy weight range and may be able to give advice regarding the safest and most effective way to achieve a target weight. Generally this will involve a combination of diet and exercise.

A few exercise precautions are in order for people with type 1 diabetes, especially those with hypoglycemia unawareness (difficulty sensing low glucose).

• Adequate intake of water, lean protein, “good” fats (monounsaturated and omega-3) and high-fiber, nutrient-rich complex carbohydrates
  

  

• Restrictions on alcohol, avoidance of artificial trans fats, and reduced intake of sugar, starches, processed foods, fast food and saturated fats
  
  
• An adequate breakfast and several small meals and nutritious snacks during the day, rather than two or three large meals

The coexistence of type 1 diabetes and insulin resistance may complicate the long-term treatment of patients with double diabetes. Patients with type 1 diabetes require regular insulin therapy. However, insulin promotes weight gain, and patients with double diabetes may not be able to use all the insulin that is supplied to the body. This means that patients may require more insulin to control their glucose (blood sugar) and may face the consequences of hyperinsulinemia.

The U.S. Food and Drug Administration (FDA) has approved oral antidiabetic agents only to treat type 2 diabetes. They cannot address the autoimmune dysfunction of type 1 diabetes, but they are sometimes prescribed off-label (in a manner other than that for which they were intended) for insulin resistance.

In some cases, a physician may recommend diet pills to promote weight loss. Patients who have developed high blood pressure or an unhealthy lipid profile may be prescribed antihypertensives or cholesterol drugs. For severe cases of obesity that noninvasive treatments cannot resolve, bariatric surgery is sometimes recommended.

Preparing questions in advance can help patients have more meaningful discussions with their physicians regarding their condition. Patients may wish to ask their doctor the following questions about double diabetes:

1. Am I at risk for double diabetes?
   
   
2. How do I avoid developing double diabetes if I have type 1 diabetes?
   
   
3. How do you know that my symptoms are caused by double diabetes?
   
   
4. Do I need to lose weight? How much, and at what pace?
   
   
5. What exercise program should I follow?
   
   
6. How should I improve my diet? Should I consult a registered dietitian? Can you recommend one?
   
   
7. What tests will you use to diagnose my condition? Do I need to do anything to prepare for these tests?
   
   
8. What are my treatment options, and which do you recommend?
   
   
9. Are others in my family at a higher risk for double diabetes? Should they be tested?
   
   
10. If my child has double diabetes, what else do I need to know?