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How Does Diabetes Mellitus Occur? Types and Their Causes

Diabetes Mellitus
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Diabetes Mellitus is a group of conditions in which blood glucose (blood sugar) is too high. It can develop at any age. Insulin, a hormone made by the pancreas, helps keep the amount of glucose in your blood in a healthy range.

Your body breaks down most of the food you eat, especially carbohydrates, into glucose. According to the CDC, glucose enters the bloodstream and insulin lets it into your cells, where it is used for energy.

Glucose is the body's main source of energy, but too much of it in the blood is harmful. Over time, high blood glucose can damage the heart, blood vessels, kidneys, nerves, feet and eyes. The CDC calls diabetes the No. 1 cause of kidney failure, lower-limb amputations and adult blindness.

How Glucose Is Maintained In Blood By Insulin?

Insulin is made by the beta cells of the pancreas. When blood glucose rises after a meal, the pancreas releases insulin, which helps glucose move into muscle, fat and liver cells. This keeps blood glucose from climbing too high.

In diabetes mellitus, the body makes too little or no insulin, or the cells don't respond to insulin well. Glucose then builds up in the blood, which leads to high blood sugar and, over time, damage to blood vessels and organs.

Another hormone, glucagon, works in the opposite direction. It raises blood glucose by signaling the liver to release stored glucose. In healthy people, insulin and glucagon work together to keep blood sugar balanced.

Types of Diabetes Mellitus

The main types of diabetes are type 1, type 2 and gestational diabetes. There are also less common types.

Type 1 diabetes mellitus

Type 1 Diabetes happens when the immune system destroys the insulin-making beta cells of the pancreas, so the body makes little or no insulin. NIDDK says type 1 is usually diagnosed in children and young adults, but it can appear at any age. People with type 1 need insulin every day.

Type 2 diabetes mellitus

Type 2 Diabetes happens when the body's cells don't use insulin well and the pancreas can't make enough extra insulin to make up for it. It is the most common type, accounting for about 90% to 95% of cases. It is linked to excess weight and family history and can develop at any age, including childhood.

Gestational diabetes mellitus

Gestational diabetes mellitus develops during pregnancy in people who did not have diabetes before. Pregnancy hormones can make the body less able to use insulin. It usually goes away after birth but raises the chance of type 2 diabetes later.

Juvenile diabetes

"Juvenile diabetes" is an older name for type 1 diabetes, not a separate type. It was used because type 1 is often diagnosed in childhood.

A few rare forms of diabetes do appear in newborns or young people because of a change in a single gene. These are called monogenic diabetes.

Causes of Diabetes Mellitus

Why is diabetes becoming so common around the world, and why does it sometimes lead to amputation? High blood glucose can damage nerves and blood flow in the feet, so small wounds may go unnoticed and heal poorly.

There is no single cause of diabetes, but the following factors may be involved:

  • For Type 1 Diabetes

    • Autoimmune destruction of beta cells
    • Family history (a parent, brother or sister with type 1)
    • Genes, possibly combined with environmental triggers such as viral infections, which are still being studied

  • For Type 2 Diabetes

    • Overweight or obesity
    • Physical inactivity
    • Unhealthy eating patterns
    • Family history
    • Older age, although it can occur at any age
    • Prediabetes

  • For Gestational diabetes

    • Family history of type 2 diabetes
    • Overweight or obesity
    • Polycystic ovary syndrome (PCOS)
    • Having had a baby weighing over 9 pounds
    • Gestational diabetes in a previous pregnancy
    • Being over 25 years old

Other types of diabetes can result from:

    • Damage to the pancreas, such as pancreatitis or surgical removal of the pancreas (pancreatectomy)
    • Cystic fibrosis
    • Steroid medicines (steroid-induced diabetes)
    • Cushing syndrome

If you have symptoms such as extreme thirst, frequent urination, blurred vision or unexplained weight loss, see a health care provider for a blood glucose test.

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