If diabetes isn't treated, it can lead to a number of other health problems.
High glucose levels can damage blood vessels, nerves and organs.
Even a mildly raised glucose level that doesn't cause any symptoms can have long-term damaging effects.
Heart disease and stroke
If you have diabetes, you're up to five times more likely to develop heart disease or have a stroke.
Prolonged, poorly controlled blood glucose levels increase the likelihood of atherosclerosis, where the blood vessels become clogged up and narrowed by fatty substances.
This may result in poor blood supply to your heart, causing angina, which is a dull, heavy or tight pain in the chest.
It also increases the chance that a blood vessel in your heart or brain will become blocked, leading to a heart attack or stroke.
High blood glucose levels can damage the tiny blood vessels in your nerves.
This can cause a tingling or burning pain that spreads from your fingers and toes up through your limbs. It can also cause numbness, which can lead to ulceration of the feet.
Damage to the peripheral nervous system, which includes all parts of the nervous system that lie outside the central nervous system, is known as peripheral neuropathy.
If the nerves in your digestive system are affected, you may experience nausea, vomiting, diarrhoea or constipation.
Diabetic retinopathy is when the retina, the light-sensitive layer of tissue at the back of the eye, becomes damaged.
Blood vessels in the retina can become blocked or leaky, or can grow haphazardly. This prevents light fully passing through to your retina. If it isn't treated, it can damage your vision.
Annual eye checks are usually organised by a regional photographic unit. If significant damage is detected, you may be referred to a doctor who specialises in treating eye conditions (ophthalmologist).
The better you control your blood glucose levels, the lower your risk of developing serious eye problems.
Diabetic retinopathy can be managed using laser treatment if it's caught early enough. However, this will only preserve the sight you have rather than improve it.
If the small blood vessels of your kidney become blocked and leaky, your kidneys will work less efficiently.
It's usually associated with high blood pressure, and treating this is a key part of management.
In rare, severe cases, kidney disease can lead to kidney failure. This can mean a kidney replacement, treatment with dialysis or sometimes kidney transplantation becomes necessary.
Damage to the nerves of the foot can mean small nicks and cuts aren't noticed and this, in combination with poor circulation, can lead to a foot ulcer.
About 1 in 10 people with diabetes get a foot ulcer, which can cause a serious infection.
If you have diabetes, look out for sores and cuts that don't heal, puffiness or swelling, and skin that feels hot to the touch. You should also have your feet examined at least once a year.
If poor circulation or nerve damage is detected, check your feet every day and report any changes to your doctor, nurse or podiatrist.
Read more about foot care and diabetes.
In men with diabetes, particularly those who smoke, nerve and blood vessel damage can lead to erection problems. This can usually be treated with medication.
Women with diabetes may experience:
If you experience a lack of vaginal lubrication or find sex painful, you can use a vaginal lubricant or a water-based gel.
Miscarriage and stillbirth
Pregnant women with diabetes have an increased risk of miscarriage and stillbirth.
If your blood glucose level isn't carefully controlled during the early stages of pregnancy, there's also an increased risk of the baby developing a birth defect.
Pregnant women with diabetes will usually have their antenatal check-ups in hospital or a diabetic clinic, ideally with a doctor who specialises in pregnancy care (an obstetrician).
This will allow your care team to keep a close eye on your blood glucose levels and control your insulin dosage more easily, as well as monitoring the growth and development of your baby.
The Diabetes UK website has more information about diabetes complications.
Looking after your eyes
The NHS diabetic eye screening programme will arrange for you to have your eyes checked every year.
Everyone who is on a diabetes register will be given the opportunity to have a digital picture taken of the back of their eye. Speak to your GP to register.