Diabetes is a chronic disease that occurs when the body cannot produce enough insulin or cannot
use insulin effectively.1 Insulin is a hormone produced in the pancreas that allows glucose from
food to enter the body’s cells where it is converted into energy needed by muscles and tissues
to function. A person with diabetes does not absorb glucose properly, and glucose remains
circulating in the blood (a condition known as hyperglycaemia) damaging body tissues over time.
This damage can lead to disabling and life-threatening health complications.
There are three main types of diabetes:
• type 1 diabetes
• type 2 diabetes
• gestational diabetes
Type 1 diabetes
Type 1 diabetes is caused by an autoimmune reaction, where the body’s defence system attacks
the insulin-producing beta cells in the pancreas. As a result, the body can no longer produce
the insulin it needs. Why this occurs is not fully understood. The disease can affect people of
any age, but usually occurs in children or young adults. People with this form of diabetes need
insulin every day in order to control the levels of glucose in their blood. Without
insulin, a person with type 1 diabetes will die.
Type 1 diabetes often develops suddenly and can produce symptoms such as:
• abnormal thirst and a dry mouth
• frequent urination
• lack of energy, extreme tiredness
• constant hunger
• sudden weight loss
• slow-healing wounds
• recurrent infections
• blurred vision
People with type 1 diabetes can lead a normal, healthy life through a combination of daily
insulin therapy, close monitoring, a healthy diet, and regular physical exercise.
The number of people who develop type 1 diabetes is increasing. The reasons for this are still
unclear but may be due to changes in environmental risk factors, early events in the womb, diet
early in life, or viral infections.
Type 2 diabetes
Type 2 diabetes is the most common type of diabetes. It usually occurs in adults, but is
increasingly seen in children and adolescents. In type 2 diabetes, the body is able to produce
insulin but either this is not sufficient or the body is unable to respond to its effects (also
known as insulin resistance), leading to a build-up of glucose in the blood.
Many people with type 2 diabetes remain unaware of their illness for a long time because
symptoms may take years to appear or be recognised, during which time the body is being damaged
by excess blood glucose. They are often diagnosed only when complications of diabetes have
already developed (see below, Diabetes complications).
Although the reasons for developing type 2 diabetes are still not known, there are several
important risk factors. These include:
• obesity
• poor diet
• physical inactivity
• advancing age
• family history of diabetes
• ethnicity
• high blood glucose during pregnancy affecting the unborn child
In contrast to people with type 1 diabetes, the majority of those with type 2 diabetes usually
do
not require daily doses of insulin to survive. Many people are able to manage their condition
through a healthy diet and increased physical activity or oral medication. However, if they are
unable to regulate their blood glucose levels, they may be prescribed insulin.
The number of people with type 2 diabetes is growing rapidly worldwide. This rise is associated
with economic development, ageing populations, increasing urbanisation, dietary changes, reduced
physical activity, and changes in other lifestyle patterns.2
Gestational diabetes
Women who develop a resistance to insulin and subsequent high blood glucose during pregnancy
are said to have gestational diabetes (also referred to as gestational diabetes mellitus or
GDM). Gestational diabetes tends to occur around the 24th week of pregnancy. The condition arises
because the action of insulin is blocked, probably by hormones produced by the placenta.
As gestational diabetes normally develops later in pregnancy, the unborn baby is already wellformed but still growing. The immediate risk to the baby is therefore not as severe as for those
whose mother had type 1 diabetes or type 2 diabetes before pregnancy (a condition known as
diabetes in pregnancy). Nonetheless, uncontrolled gestational diabetes can have serious
consequences for both the mother and her baby. Poorly managed blood glucose during pregnancy
can lead to a significantly larger than average baby (a condition known as fetal macrosomia),
which makes a normal birth difficult and risky. The newborn will be at risk for shoulder injury
and breathing problems. In many cases, a caesarean section is necessary, putting the mother’s
health at risk, particularly in low-resource settings, where access to good healthcare is
limited. For women living in outlying rural areas there is a life-threatening risk from
prolonged obstructed labour. There also exists the risk of preeclampsia, a condition
where sudden high blood pressure threatens the health (and in some cases the life) of the mother
and her baby. Gestational diabetes in mothers normally disappears after birth. However, women
who have had gestational diabetes are at a higher risk of developing gestational diabetes in
subsequent pregnancies and of developing type 2 diabetes later in life. Babies born to mothers
with gestational diabetes also have a higher lifetime risk of obesity
and developing type 2 diabetes. Women with gestational diabetes or diabetes in pregnancy need to
monitor and control their blood glucose levels to minimise risks to the baby.
Normally, this can be done by taking up a healthy diet and moderate exercise, but in some cases
insulin or oral medication may be needed as well.
Impaired glucose tolerance and
impaired fasting glucose
People whose blood glucose levels are high but not as high as those in people with diabetes are
said to have impaired glucose tolerance (commonly referred to as IGT) or impaired fasting
glucose (IFG). IGT is defined as high blood glucose levels after eating; whereas IFG is defined
as high blood glucose after a period of fasting. The term ‘prediabetes’ is also used to
describe people with these conditions – a ‘grey area’ between normal glucose
levels and diabetes. People with IGT are at high risk of developing type 2 diabetes.
Unsurprisingly, IGT shares many characteristics with type 2 diabetes and is associated with
obesity, advancing age and the inability of the body to use the insulin it produces. Not
everyone with IGT goes on to develop type 2 diabetes: a large bank of evidence supports the
effectiveness of lifestyle interventions – healthy diet and physical exercise
– to prevent the progression to diabetes.3
Diabetes complications
People with diabetes are at risk of developing a number of disabling and life-threatening health
problems. Consistently high blood glucose levels can lead to serious diseases affecting the
heart and blood vessels, eyes, kidneys, and nerves. People with diabetes are also at increased
risk of developing infections. In almost all high-income countries, diabetes is a leading cause
of cardiovascular disease, blindness, kidney failure, and lower-limb amputation. As the
prevalence of type 2 diabetes grows in low- and middle-income countries, so too does the impact
of these costly – in both human and economic terms – complications.
Maintaining blood glucose levels, blood pressure and cholesterol close to normal can
help delay or prevent diabetes complications. People with diabetes need regular monitoring for
complications.
Cardiovascular disease
Cardiovascular disease is the most common cause of death and disability among people with
diabetes. The cardiovascular diseases that accompany diabetes include angina, myocardial
infarction (heart attack), stroke, peripheral artery disease, and congestive heart failure. In
people with diabetes, high blood pressure, high cholesterol, high blood glucose and other risk
factors contribute to the increased risk of cardiovascular complications.
Kidney disease
Kidney disease (nephropathy) is far more common in people with diabetes than in people without
diabetes; and diabetes is one of the leading causes of chronic kidney disease. The disease is
caused by damage to small blood vessels, which can cause the kidneys to be less efficient, or to
fail altogether. Maintaining near-normal levels of blood glucose and blood pressure can greatly
reduce the risk of nephropathy.
Eye disease
Many people with diabetes develop some form of eye disease (retinopathy), which can damage
vision or provoke blindness. Persistently high levels of blood glucose, together with high blood
pressure and high cholesterol, are the main causes of retinopathy. The network of blood vessels
that supply the retina can become blocked and damaged in retinopathy, leading to permanent loss
of vision. Retinopathy can be managed through regular eye checks and by keeping blood glucose
levels close to normal.
Nerve damage
When blood glucose and blood pressure are excessively high, diabetes can provoke damage to
nerves throughout the body (neuropathy). This damage can lead to problems with digestion and
urination, erectile dysfunction and a number of other functions. The most commonly affected
areas are the extremities, particularly the feet. Nerve damage in these areas is called
peripheral neuropathy, and can lead to pain, tingling, and loss of feeling. Loss
of feeling is particularly dangerous because it can allow injuries to go unnoticed, leading to
serious infections and ulceration, diabetic foot disease, and major amputations.
Diabetic foot
People with diabetes may develop a number of different foot problems as a result of damage to
nerves and blood vessels. These problems can easily lead to infection and ulceration, which
increase a person’s risk of amputation. People with diabetes face a risk of amputation that may
be more than 25 times greater than that in people without diabetes.4 However, with good
management, a large proportion of amputations can be prevented. Even when a person undergoes
amputation, the remaining leg – and the person’s life – can be saved by good follow-up care
from a multidisciplinary foot team.4 People with diabetes must examine their feet regularly.
Pregnancy complications
Women with any type of diabetes during pregnancy risk a number of complications if they do
not carefully monitor and manage their condition. Women with diabetes require detailed planning
and close monitoring before and during pregnancy to minimise complications. High blood glucose
during pregnancy can lead to fetal abnormalities and cause it to gain excess size and weight,
and overproduce insulin. These can lead to problems at delivery, injuries to the child and
mother, and a sudden drop in blood glucose (hypoglycaemia) in the child after birth. Children
who are exposed for a long time to high blood glucose in the womb are at higher risk of
developing type 2 diabetes later in life.