Diabetes occurs when the body has trouble using the sugar it gets from food for energy. Sugar builds up in the bloodstream. High blood sugar can have immediate effects, like blurry vision. It can also cause problems over time, like heart disease and blindness.

There are two main types of diabetes: type 1 diabetes and type 2 diabetes. Both are caused by problems making or using insulin, a hormone that makes it possible for cells to use glucose, also known as blood sugar, for energy.


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What is diabetes?

Diabetes (known formally as diabetes mellitus) is a chronic illness affecting more than 37 million Americans—about one out of every 10 people. Its primary feature is high blood sugar levels, also called blood glucose levels. But what is glucose, and how is having too much of it in your bloodstream harmful?

When you digest your food, chemical processes take place in your body that break down food, primarily carbohydrates, into sugars, or glucose. Glucose is an important fuel for cells throughout your body. But those cells can’t get access to this critical fuel source without a substance, produced naturally by your pancreas, called insulin.

In someone without diabetes, an increase in blood sugar, usually after a meal, causes the pancreas to release insulin into the bloodstream so that glucose can move into the body’s cells and be used as fuel. Once the sugar is in the cells and no longer in the bloodstream, the person has normal glucose levels.

But with diabetes, that process stops working, either because the pancreas fails to produce sufficient insulin, or because the body’s cells become resistant to insulin (or both). As a result, the glucose, unable to enter the cells, lingers in the bloodstream, circulating throughout the body and causing damage to blood vessels, nerves and organs.

How is diabetes diagnosed? Normally, adults have their blood-sugar levels monitored as part of their regular wellness checkups. Several tests may be used to diagnose diabetes, including those that assess sugar levels while fasting, after having consumed sugar, at random times or as an average over recent months. If a patient does not have normal blood sugar levels—especially if they’re experiencing symptoms—they will likely be diagnosed with diabetes or pre-diabetes.

However, sometimes diabetes is not detected until someone shows high blood sugar symptoms. The two most common symptoms are excessive urination and increased thirst. If left untreated, it can lead to dehydration, confusion, and extreme weakness.

What is prediabetes?

Just as the name implies, pre-diabetes is a condition that’s often—though not always—a precursor to full-blown diabetes. If you’re diagnosed with prediabetes, that’s a warning sign to manage your blood sugar levels through lifestyle changes and possibly medication to prevent it from developing into diabetes.

How is prediabetes diagnosed? Doctors use the same tests for prediabetes as they do for diabetes. Most such tests measure the amount of glucose in the blood, expressed as micrograms per deciliter, or mc/dL. A reading above the normal range but not yet in the range of diabetes results in a prediabetes diagnosis. For example, on a fasting glucose test, a normal level would be below 100 mc/dL, prediabetes would be diagnosed for someone in the range of 100-125 mc/dL, and someone with a result higher than 125 mc/dL would receive a diabetes diagnosis.

Another test to diagnose prediabetes is a blood test that measures hemoglobin A1C (HbA1c). This test can be done any time during the day and does not require fasting. It reflects your average blood sugar over the past three months. A normal reading is below 5.7%. A reading of 5.7% to 6.4% means prediabetes, and people with diabetes have reading of 6.5% or higher.

About one in 10 people diagnosed with prediabetes will go on to develop type 2 diabetes in the next 12 months. The lifetime risk of this happening is about 70%. Fortunately, however, a prediabetes diagnosis does not mean you’re destined to develop diabetes.

It’s possible not only to avoid developing diabetes but to reverse prediabetes. The key is to battle insulin resistance, which is linked to body fat, especially around the belly. Therefore, regular exercise—at least 30 minutes each day—and eating healthy foods are crucial.

While there is no prescribed “prediabetes diet,” there are certain guidelines you should follow to help avoid disease progression. For example, eating too many carbohydrates—especially of the refined and processed varieties—will cause your blood sugar to spike. Vegetables, beans and whole grains are good forms of carbohydrates. Eating too many calories causes your body to store the extra energy as fat, making insulin resistance worse. So get your protein from lean meats, poultry, fish and legumes. Avoid sugary beverages and instead drink lots of water.

What are the symptoms of diabetes?

Diabetes symptoms don’t always appear until the disease has progressed, which is why it’s important to have a periodic wellness visit with your primary care clinician that includes lab work. The earlier the disease is detected, the better able you’ll be to manage it.

One of the key diabetes signs is a cluster of symptoms that include excessive thirst and urination. This happens because the kidneys must release the extra glucose into the urine. That means the kidneys need to also release large amounts of water along with the glucose. Expelling so much fluid makes you dehydrated, which is why you become so thirsty.

Sometimes, because the cells are deprived of glucose, they turn to another fuel source called ketones, which are produced by the liver. Ketones are acidic, and an accumulation of them in the bloodstream can lead to a dangerous condition called ketoacidosis

Long-term, diabetes can cause several serious health problems. Excessive blood sugar damages blood vessels in the eyes, causing a condition called retinopathy, which can lead to blindness if left untreated. High blood glucose also damages nerves, often in the feet, legs and hands. People with diabetes sometimes develop sores on their feet which they cannot feel because of nerve damage. When those sores go untreated, they can become deep skin ulcers that can take months to heal. Also, diabetes raises the risk of heart and kidney disease.

What’s the difference between Type 1 diabetes and Type 2 diabetes?

Both type 1 diabetes and type 2 diabetes share the key connection between blood sugar and insulin. And the same criteria are used to diagnose both types. But the reasons why each happens differs.

During digestion, food is broken down into basic components. Carbohydrates are broken down into simple sugars, primarily glucose. Glucose is a critically important source of energy for the body's cells. To provide energy to the cells, glucose needs to leave the blood and get inside the cells.

The hormone insulin produced by the pancreas and released into the bloodstream signals the body’s cells to take up glucose. When levels of glucose in the blood rise, like following a meal, the pancreas normally produces more insulin.

Type 1 diabetes occurs when some or all of the insulin-producing cells in the pancreas are destroyed. This leaves the patient with little or no insulin. Without insulin, sugar accumulates in the bloodstream rather than entering the cells. As a result, the body cannot use this glucose for energy. In addition, the high levels of glucose that remain in the blood cause excessive urination and dehydration, and damage tissues of the body.

Type 1 diabetes is an autoimmune disease. This means it begins when the body's immune system attacks cells in the body. In type 1 diabetes, the immune system destroys insulin-producing cells (beta cells) in the pancreas.  

Type 2 diabetes occurs when your body's cells resist the normal effect of insulin, which is to drive glucose in the blood into the inside of the cells. This condition is called insulin resistance. As a result, glucose starts to build up in the blood.

In people with insulin resistance, the pancreas "sees" the blood glucose level rising. The pancreas responds by making extra insulin to maintain a normal blood sugar. Over time, the body's insulin resistance gets worse. In response the pancreas makes more and more insulin. Finally, the pancreas gets "exhausted".  It cannot keep up with the demand for more and more insulin. It poops out.  As a result, blood glucose levels start to rise.

Can diabetes be prevented?

Type 1 diabetes cannot be prevented. But you can prevent type 2 diabetes even if it runs in your family.

If a close relative—particularly, a parent or sibling—has type 2 diabetes, or if your blood glucose test shows “pre-diabetes” (defined as blood glucose levels between 100 and 125 mg/dL), you are at increased risk for developing type 2 diabetes. You can help to prevent type 2 diabetes by

  • maintaining your ideal body weight.
  • exercising regularly—such as a brisk walk of 1-2 miles in 30 minutes—at least five times a week, even if that does not result in you achieving an ideal weight. That’s because regular exercise reduces insulin resistance even if you don’t lose weight.
  • eating a healthy diet.
  • taking medication. The medication metformin (Glucophage) offers some additional protection for people with pre-diabetes.

If you already have type 2 diabetes, you can still delay or prevent complications by doing the following.

Keep control of your blood sugar. This helps reduce the risk of most complications.

Lower your risk of heart-related complications. Aggressively manage other risk factors for atherosclerosis, such as:

  • high blood pressure
  • high cholesterol and triglycerides
  • cigarette smoking
  • obesity

Visit an eye doctor and a get a foot exam every year. This can help you reduce the risk of eye and foot complications.

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