Diabetes mellitus refers to a group of diseases that affect how the body uses blood sugar (glucose). Glucose is an important source of energy for the cells that make up the muscles and tissues. It’s also the brain’s main source of fuel.

The main cause of diabetes varies by type. But no matter what type of diabetes you have, it can lead to excess sugar in the blood. Too much sugar in the blood can lead to serious health problems.

Chronic diabetes conditions include type 1 diabetes and type 2 diabetes. Potentially reversible diabetes conditions include prediabetes and gestational diabetes. Prediabetes happens when blood sugar levels are higher than normal. But the blood sugar levels aren’t high enough to be called diabetes. And prediabetes can lead to diabetes unless steps are taken to prevent it. Gestational diabetes happens during pregnancy. But it may go away after the baby is born.

Symptoms

Diabetes symptoms depend on how high your blood sugar is. Some people, especially if they have prediabetes or type 2 diabetes, may not have symptoms. In type 1 diabetes, symptoms tend to come on quickly and be more severe.

Some of the symptoms of type 1 diabetes and type 2 diabetes are:

• Feeling more thirsty than usual.
• Urinating often.
• Losing weight without trying.
• Presence of ketones in the urine. Ketones are a byproduct of the breakdown of muscle and fat that happens when there’s not enough available insulin.
• Feeling tired and weak.
• Feeling irritable or having other mood changes.
• Having blurry vision.
• Having slow-healing sores.
• Getting a lot of infections, such as gum, skin and vaginal infections.

Type 1 diabetes can start at any age. But it often starts during childhood or teen years. Type 2 diabetes, the more common type, can develop at any age. Type 2 diabetes is more common in people older than 40.

When to see a doctor

• If you think you or your child may have diabetes.If you notice any possible diabetes symptoms, contact your health care provider. The earlier the condition is diagnosed, the sooner treatment can begin.

If you’ve already been diagnosed with diabetes. After you receive your diagnosis, you’ll need close medical follow-up until your blood sugar levels stabilize.

Causes

To understand diabetes, it’s important to understand how the body normally uses glucose.

How insulin works

Insulin is a hormone that comes from a gland behind and below the stomach (pancreas).

• The pancreas releases insulin into the bloodstream.
• The insulin circulates, letting sugar enter the cells.
• Insulin lowers the amount of sugar in the bloodstream.
• As the blood sugar level drops, so does the secretion of insulin from the pancreas.

The role of glucose

Glucose — a sugar — is a source of energy for the cells that make up muscles and other tissues.

• Glucose comes from two major sources: food and the liver.
• Sugar is absorbed into the bloodstream, where it enters cells with the help of insulin.
• The liver stores and makes glucose.
• When glucose levels are low, such as when you haven’t eaten in a while, the liver breaks down stored glycogen into glucose. This keeps your glucose level within a typical range.

The exact cause of most types of diabetes is unknown. In all cases, sugar builds up in the bloodstream. This is because the pancreas doesn’t produce enough insulin. Both type 1 and type 2 diabetes may be caused by a combination of genetic or environmental factors. It is unclear what those factors may be