Learning about insulin is essential to successfully managing type 2 diabetes. Insulin controls the level of sugar, or glucose, in your blood. Normally, the body works to balance how much insulin it makes with how much it needs. But when you have diabetes, your body needs help to keep this balance.

Insulin and Your Body

When you eat, your blood sugar level rises. That's because the food you eat is broken down into sugar. Normally, certain cells in your pancreas produce insulin so your body can move that sugar from your blood into cells throughout your body, where it can either be used as energy or stored.

With type 2 diabetes, however, your body either doesn't make enough insulin or doesn't use it properly. When your body can’t effectively use the insulin it makes, the complication is known as insulin resistance.

When you first develop insulin resistance, your pancreas responds by increasing insulin production. This can help bring the level of sugar in your blood back down to normal levels. Over time, however, insulin resistance can lead to type 2 diabetes because the cells in your body that produce insulin may no longer be able to keep up with your body's rising demand for the hormone.

Insulin and Blood Sugar

Without enough insulin, sugar builds up in your blood causing high blood sugar levels. Over time, uncontrolled high blood sugar levels can lead to serious health problems such as stroke, heart disease, and nerve damage.

Some people with type 2 diabetes can control their condition with a combination of diet, exercise, and medication. Avoiding simple carbohydrates (i.e., processed foods like white bread, cake, cookies, and other sugary foods) and instead eating more complex carbohydrates (i.e., whole grains and non-starchy vegetables like broccoli, asparagus, and carrots) can also help because complex carbohydrates are broken down into sugar more slowly. Regular exercise and losing excess weight can also help your body become more sensitive to the insulin it produces.

If diet and exercise alone aren’t enough, certain medications can help your body produce more insulin and become less insulin resistant. But if these treatment options aren't able to keep blood sugar levels in check, insulin therapy may be needed, says Leann Olansky, MD, an endocrinologist at the Cleveland Clinic in Ohio.

How Insulin Therapy Works

There are many types of insulin of varying strengths available. Although they all reduce blood sugar levels, they differ in how quickly they work, when they peak, and how long they last:

  • Rapid-acting insulin starts working about 15 minutes after injected and peaks about an hour later. It will continue working for up to 4 hours.
  • Regular or short-acting insulin starts working 30 minutes after injected and peaks 2 to 3 hours later. It lasts for 3 to 6 hours.
  • Intermediate-acting insulin begins working about 2 to 4 hours after injected. It won’t peak for another 4 to 12 hours and will remain effective for up to 18 hours.
  • Long-acting insulin doesn't start working for several hours after injected and continues to work over the course of 24 hours.

Your doctor will determine what type of insulin is right for you as well as how much you need and when you should take it.

"People with diabetes who have good control of their blood sugar may follow the same insulin regimen for years," Dr. Olansky says. If you start to lose control, your doctor may need to adjust the dosage or type of insulin you take.

Possible Side Effects of Insulin Therapy

Like other medications, insulin therapy may cause side effects. "Some people experience fluid retention because insulin leads to greater reabsorption of sodium," Olansky says. More significant side effects include:

Weight gain. A review of studies, published in the Canadian journal CMAJ in 2012, found that people may gain up to 14 pounds when they begin insulin therapy. The researchers noted, however, that weight gain usually occurs within the first weeks or months of treatment and then levels off.

Low blood sugar (hypoglycemia). If you have low blood sugar, your blood sugar level has dropped too low. Also known as insulin shock, in extreme cases it can lead to coma or even death. What you eat and how active you are can affect your insulin sensitivity and risk for hypoglycemia. For example, if you’re normally sedentary and you go shopping for the afternoon, taking your normal dose of insulin could lead to low blood sugar. Olansky says that people who use insulin need to understand this interaction, anticipate the risk for hypoglycemia, and take steps to prevent their blood sugar from dropping too low, like packing an extra snack before leaving home.