Course and prognosis of diabetes

Diabetes can now be controlled with great success.
Diabetes can now be controlled with great success.

Course of type 1 diabetes

For more than 25 years, it has been proposed that type 1 diabetes is the result of both genetic and environmental factors. These factors can lead to an autoimmune reaction in which the pancreatic beta cells are destroyed, leading to type 1 diabetes and a lifelong dependence on insulin.

In both children and adults, the rate of progression from the onset of beta-cell destruction to glucose intolerance, and then to symptomatic disease, is variable. We now know that this process can last from only a few months to several decades.

With new and ongoing studies, type 1 diabetes can be identified at earlier, pre-symptomatic stages. The condition can now also be staged, starting with the detection of two or more islet auto-antibodies in the blood (stage 1) and progressing at a variable rate to a second stage of glucose intolerance or an abnormality in blood-glucose stability (stage 2), before becoming clinically symptomatic (stage 3).

Stage 3 represents manifestations of the typical symptoms and signs of diabetes, which may include frequent urination, excessive thirst, weight loss and fatigue.

Prognosis of type 1 diabetes

Untreated type 1 diabetes is a fatal condition as a result of diabetic ketoacidosis – a complication that is characterised by severe disturbances in carbohydrate, protein and fat metabolism. Poorly controlled type 1 diabetes is a risk factor for chronic complications such as blindness, renal failure, foot amputation, and heart attack.

But there is good news: in type 1 diabetes, the incidence of microvascular disease (e.g. damage to the smaller blood vessels) and macrovascular disease (e.g. damage to the large blood vessels) can be dramatically reduced with tight control of blood-glucose levels.

If you manage to control your condition well, the decreased incidence of macrovascular disease can persist for up to 30 years. Even a few years of intensive glucose control translates into reduced rates of microvascular and macrovascular complications 10 years later. Most people with type 1 diabetes should aim to achieve and maintain a target HbA1c of less than 7% to prevent microvascular disease.

Cardiovascular disease (CVD), which falls into the macrovascular disease category, is a major cause of death and morbidity in people with diabetes. CVD includes heart disease, stroke and all other diseases of the heart and circulation, including hardening and narrowing of the arteries supplying blood to the legs (peripheral arterial disease).

One analysis of people with type 1 diabetes who were diagnosed before the age of 15 found that the leading cause of death before the age of 30 years was acute complications of diabetes. After the age of 30, CVD was predominant – although death attributable to acute complications was still important in this age group.

Life expectancy is reduced, on average, by more than 20 years in people with type 1 diabetes who have not controlled their condition. It’s also worth taking note of the risks during pregnancy. Babies of women with type 1 diabetes are:

  • Five times as likely to be stillborn.
  • Three times as likely to die in their first few months of life.
  • Twice as likely to have a major congenital anomaly.

However, with careful planning and adequate treatment, most women with type 1 diabetes can have successful pregnancies.

Course of type 2 diabetes

Type 2 diabetes can be a progressive disease in which the risks of macrovascular disease, microvascular disease and death are all strongly associated with hyperglycaemia (elevated blood glucose levels).

The course of the disease is characterised by a decline in beta-cell function and progressive insulin resistance – when the cells in the muscles, fat and liver don’t respond well to insulin and can’t easily take up glucose from the blood.

The process involves the degeneration of multiple parameters, including haemoglobin A1C (HbA1c), fasting blood glucose (i.e. your blood-glucose levels after a period of fasting) and postprandial glucose levels (i.e. your blood-glucose levels after consuming a meal).

In type 2 diabetes, the beta cells in the pancreas fail to adjust to impaired glucose tolerance, which leads to a decline in their function. Progressive loss of beta-cell function and, to a lesser extent, reduced beta-cell mass, lead to worsening glycaemic control and the development of complications.

Many of the current therapies don’t completely stop this progressive loss of beta-cell function, even though they lower blood-glucose levels, and unfortunately their use is also associated with hypoglycaemia (low blood glucose) and weight gain. 

Prognosis of type 2 diabetes

By the time they’re diagnosed, 50% of people with type 2 diabetes already show signs of complications. These complications may begin 5-6 years before diagnosis, while the diabetes itself may start 10 years or more before the clinical diagnosis is made.

CVD is a major cause of death and disability in people with type 2 diabetes, accounting for 52% of fatalities in this group. People with type 2 diabetes have a two-fold increased risk of stroke within the first five years of diagnosis compared with the general population.

Other possible complications include:

  • Kidney disease. Diabetes is the single most common cause of end-stage kidney disease and about one in three people with type 2 diabetes develop overt kidney disease. Kidney disease accounts for 11% of deaths in people with type 2 diabetes.
  • Depression. The prevalence of depression is approximately twice as high in people with diabetes as it is in the general population.
  • Neuropathy (nerve damage). Damage to the nerves that transmit impulses to and from the brain and spinal cord to the muscles, skin, blood vessels and other organs may affect up to 50% of people with diabetes. It can also cause erectile dysfunction and chronic pain.
  • Limb amputation. Diabetes is the most common cause of lower-limb amputation. About one in every 20 people with diabetes will develop a foot ulcer in any given year and more than one in ten foot ulcers result in the amputation of a foot or leg. Up to 70% of people die within five years of having an amputation as a result of diabetes.

Life expectancy is reduced, on average, by up to 10 years in people with type 2 diabetes.

Course of gestational diabetes

Gestational diabetes is a form of diabetes that causes high blood glucose levels during pregnancy. If left untreated, it can lead to several complications for both mother and baby.

The mother is at increased risk for pre-eclampsia, a condition characterised by high blood pressure, and there’s an increased risk of birth complications, including premature birth, still birth, macrosomia (a large baby), hypoglycaemia of the newborn, jaundice and mineral deficiencies.

Researchers have found that women who gain excessive amounts of weight later in pregnancy (between 28 and 36 weeks) are more likely to have a difficult labour, requiring interventions such as forceps delivery and instrumental delivery, which may lead to injury. The effects on the baby are also more significant, with a greater risk of high birth weight. The risk for complications is reduced immensely with tight blood glucose control and weight management. In most cases, the gestational diabetes is resolved after the baby is born.

Prognosis of gestational diabetes

A previous diagnosis of gestational diabetes carries a lifetime risk of progression to type 2 diabetes. In fact, women with a history of gestational diabetes are around seven times more likely to develop type 2 diabetes than women who had a normal pregnancy. If the woman with gestational diabetes needed insulin injections to control her blood glucose during pregnancy, her risk for type 2 diabetes is further increased.

When compared to women who don’t develop gestational diabetes, women with a history of the condition are also at greater risk for CVD events – especially heart attack – later in life. However, women who maintain a healthy lifestyle throughout their middle years may reduce their CVD risk, despite having a history of gestational diabetes.

The risk of a mother getting gestational diabetes again in a future pregnancy is between 30% and 84%. If the second pregnancy occurs within a year of the first, the risk of recurrence is higher.

Babies born to mothers who had gestational diabetes are at greater risk of developing obesity and type 2 diabetes later in life.

Overall prognosis of diabetes

While diabetes can reduce a person’s life expectancy, it’s a condition that can now be controlled with great success.

The general statistical prognosis is that 15% of people with type 1 diabetes will die before the age of 40. But thanks to advances in the understanding of the condition, this number is much lower than it was a few decades ago. Sensible blood glucose control, along with a healthy, active lifestyle, can help people with type 1 diabetes lead long, productive lives.

A type 2 diabetes diagnosis in your 40s cuts 5-10 years off your average life expectancy. This is also a vast improvement on what the prognosis used to be. Medical science has now also made it possible to live a full, productive life with fewer complications if you’ve been diagnosed with type 2 diabetes.  

With both type 1 and type 2 diabetes, a multi-disciplinary team approach is required to manage the condition effectively. It’s important to look for a diabetes clinic that has dedicated, appropriately trained staff, where you can do both individual consultations as well as group education sessions. There should be adequate protocols that cover screening and regular care, including referrals to other health professionals.

Apart from the recommended monitoring that should be done at your clinic or doctor’s rooms, you should also be guided in terms of vaccination (e.g. you may need to be vaccinated against influenza, pneumococcal pneumonia and hepatitis).

You should go for a yearly dental examination and visit the oral hygienist twice a year to control gum disease, which both contributes to and worsens high blood glucose levels. Gum disease is more prevalent in adults with type 2 diabetes and severe infections can lead to heart problems which, in turn, affect life expectancy.

People with autoimmune diabetes are also more likely to have thyroid disease, coeliac disease and depression. Talk to your doctor about the symptoms of these diseases and don’t delay getting treatment if you suspect you may be affected.

Information supplied by Jeannie Berg, diabetes educator and Chairperson of the Diabetes Education Society of South Africa (DESSA), and reviewed by Dr Joel Dave (MBChB PhD FCP Cert Endocrinology), Senior Specialist in the Division of Diabetic Medicine and Endocrinology, University of Cape Town. August 2018.

Read more:

Risk factors for diabetes

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