Diabetes is caused by the pancreas not producing enough insulin, or the body’s cells not reacting to insulin, according to the NHS.
Without enough insulin, glucose stays in the blood and isn’t converted into energy.
The condition puts extra strain on blood vessels and patients’ vital organs.
Without proper treatment, diabetes can increase the risk of heart disease, strokes, kidney disease and even sexual dysfunction.
Heart disease
Diabetics are up to five times more likely to develop heart disease, or have a stroke, the NHS said.
“Prolonged, poorly controlled blood glucose levels increase the likelihood of atherosclerosis, where the blood vessels become clogged up and narrowed by fatty substances,” it said.
“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.”
Nerve damage
Having too much glucose in the blood can damage tiny blood vessels in your nerves.
It can lead to a tingling, or burning pain sensation in your fingers and toes.
The NHS said: “If the nerves in your digestive system are affected, you may experience nausea, vomiting, diarrhoea or constipation.”
Kidney disease
About 40 per cent of diabetes patients develop kidney disease, according to Diabetes.co.uk.
Diabetes affects the body’s arteries, and as the kidneys filter blood from many arteries, kidney problems are a common risk for patients, it added.
“To help catch kidney disease before the later stages develop, people with diabetes should be screened for kidney complications once a year.
“The screening test involves a simple urine sample which is tested to detect whether protein is present in the urine.”
Foot ulcers
Nerve damage in your feet make it difficult to notice small cuts on your feet.
Combined with poor circulation, it can lead to a foot ulcer.
A foot ulcer is an open sore, that can be very deep.
Harvard Medical School said: “A deep foot ulcer may be a crater that extends through the full thickness of the skin. It may involve tendons, bones and other deep structures.
“Among people with diabetes, most severe foot infections that ultimately require some part of the toe, foot or lower leg to be amputated start as a foot ulcer.”
Sexual dysfunction
Men with diabetes can suffer from erectile dysfunction.
It can usually be treated with medication, but those that smoke, have nerve damage, or blood vessel damage are most at risk.
“Women with diabetes may experience a reduced sex drive, less pleasure from sex, vaginal dryness, less ability to orgasm, and pain during sex,” said the NHS.