Diabetes – Harvard Health

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 (once called juvenile-onset diabetes) and type 2 diabetes (once called adult-onset 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.

When you eat, your body breaks down carbohydrates into a simple sugar called glucose. It also produces a hormone called insulin that signals the body's cells to absorb glucose from the bloodstream. Type 1 diabetes occurs when the body doesn't make enough insulin, or stops making it altogether. Type 2 diabetes occurs when the body's cells don't respond to insulin. Either way, since sugar can't get into cells, it builds up in the bloodstream.

Too much sugar in the blood can cause a range of uncomfortable symptoms. These include:

Type 1 diabetes often comes on suddenly. It usually strikes children and teenagers, but can appear later in life. It is an autoimmune disease, meaning it happens because the body's immune system mistakenly attacks and destroys the body's insulin-making cells. Type 1 diabetes can't be cured, but it can be managed by taking insulin before eating.

Type 2 diabetes takes longer to develop. It can begin any time from childhood onward. Type 2 diabetes is usually triggered by being overweight or obese and not getting much physical activity. Treatment for type 2 diabetes includes weight loss if needed, daily exercise, a healthy diet, and medications.

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Diabetes - Harvard Health