Insulin Resistance and diabetes development

A large number of people have asked me to write about insulin resistance. No surprises. Because doctors here will be mentioning about it frequently as India is one of the countries where most number of diabetics exist.

So here we go...

Insulin is a hormone made in the pancreas, an organ located behind the stomach. The pancreas contains clusters of cells called islets of Langerhans, the regions of the pancreas that contain its endocrine (i.e., hormone-producing) cells . Beta cells within the islets make insulin and release it into the blood.

Pancreatic islets

Insulin plays a major role in metabolism—the way the body uses digested food for energy. The digestive tract breaks down carbohydrates—sugars and starches found in many foods—into glucose. Glucose is a form of sugar that enters the bloodstream. With the help of insulin, cells throughout the body absorb glucose and use it for energy.

When blood glucose levels rise after a meal, the pancreas releases insulin into the blood. Insulin and glucose then travel in the blood to cells throughout the body.

• Insulin helps muscle, fat, and liver cells absorb glucose from the bloodstream, lowering blood glucose levels.
• Insulin stimulates the liver and muscle tissue to store excess glucose. The stored form of glucose is called glycogen.
• Insulin also lowers blood glucose levels by reducing glucose production in the liver.

In a healthy person, these functions allow blood glucose and insulin levels to remain in the normal range.

In insulin resistance, muscle, fat, and liver cells do not respond properly to insulin and thus cannot easily absorb glucose from the bloodstream. As a result, the body needs higher levels of insulin to help glucose enter cells.

The beta cells in the pancreas try to keep up with this increased demand for insulin by producing more. As long as the beta cells are able to produce enough insulin to overcome the insulin resistance, blood glucose levels stay in the healthy range.

Over time, insulin resistance can lead to type 2 diabetes and prediabetes because the beta cells fail to keep up with the body's increased need for insulin. Without enough insulin, excess glucose builds up in the bloodstream, leading to diabetes, prediabetes, and other serious health disorders.

Now what causes insulin resistance?

Although the exact causes of insulin resistance are not completely understood, scientists think the major contributors to insulin resistance are excess weight and physical inactivity.

Some experts believe obesity, especially excess fat around the waist, is a primary cause of insulin resistance. Scientists used to think that fat tissue functioned solely as energy storage. However, studies have shown that belly fat produces hormones and other substances that can cause serious health problems such as insulin resistance, high blood pressure, imbalanced cholesterol, and cardiovascular disease (CVD).

Belly fat plays a part in developing chronic, or long-lasting, inflammation in the body. Chronic inflammation can damage the body over time, without any signs or symptoms. Scientists have found that complex interactions in fat tissue draw immune cells to the area and trigger low-level chronic inflammation. This inflammation can contribute to the development of insulin resistance, type 2 diabetes, and CVD. Studies show that losing the weight can reduce insulin resistance and prevent or delay type 2 diabetes.

Many studies have shown that physical inactivity is associated with insulin resistance, often leading to type 2 diabetes. In the body, more glucose is used by muscle than other tissues. Normally, active muscles burn their stored glucose for energy and refill their reserves with glucose taken from the bloodstream, keeping blood glucose levels in balance.

Studies show that after exercising, muscles become more sensitive to insulin, reversing insulin resistance and lowering blood glucose levels. Exercise also helps muscles absorb more glucose without the need for insulin. The more muscle a body has, the more glucose it can burn to control blood glucose levels.

Other causes of insulin resistance may include ethnicity, certain diseases, hormones, steroid use, some medications, older age, sleep problems- especially sleep apnea and cigarette smoking.

Insulin resistance increases the risk of developing type 2 diabetes and prediabetes. Prediabetes usually occurs in people who already have insulin resistance. Although insulin resistance alone does not cause type 2 diabetes, it often sets the stage for the disease by placing a high demand on the insulin-producing beta cells. In prediabetes, the beta cells can no longer produce enough insulin to overcome insulin resistance, causing blood glucose levels to rise above the normal range.

Once a person has prediabetes, continued loss of beta cell function usually leads to type 2 diabetes. People with type 2 diabetes have high blood glucose. Over time, high blood glucose damages nerves and blood vessels, leading to complications such as heart disease, stroke, blindness, kidney failure, and lower-limb amputations.

Research has shown that most people with prediabetes develop type 2 diabetes within 10 years, unless they change their lifestyle. Lifestyle changes include losing 5 to 7 percent of their body weight by making changes in their diet and level of physical activity.

Insulin resistance and prediabetes usually have no symptoms. People may have one or both conditions for several years without knowing they have them. Going for tests is the only way to tell whether a person has prediabetes or diabetes. 

However, people with a severe form of insulin resistance may have dark patches of skin, usually on the back of the neck. Sometimes people have a dark ring around their neck. Dark patches may also appear on elbows, knees, knuckles, and armpits. This condition is called acanthosis nigricans.

What are the risk factors for prediabetes?

In addition to being overweight or obese or being age 45 or older— the risk factors include the following: being physically inactive, having a parent or sibling with diabetes, having a family background of diabetic predisposition, giving birth to a baby weighing more than 9 pounds, being diagnosed with gestational diabetes—diabetes that develops only during pregnancy, having high blood pressure—140/90 mmHg or above—or being treated for high blood pressure, HDL cholesterol level below 35 mg/dL or a triglyceride level above 250 mg/dL, having polycystic ovary syndrome (PCOS), having prediabetes, impaired fasting glucose (IFG), or impaired glucose tolerance (IGT) on an earlier testing, having other conditions associated with insulin resistance, such as obesity or acanthosis nigricans, having Cardio vascular disease (CVD).

Metabolic syndrome, also called insulin resistance syndrome, is a group of traits and medical conditions linked to overweight and obesity that puts people at risk for both CVD and type 2 diabetes. Metabolic syndrome is defined as the presence of any three of the following:

• large waist size—waist measurement of 40 inches or more for men and 35 inches or more for women
• high triglycerides in the blood—triglyceride level of 150 milligrams per deciliter (mg/dL) or above, or taking medication for elevated triglyceride level
• abnormal levels of cholesterol in the blood—HDL, or good, cholesterol level below 40 mg/dL for men and below 50 mg/dL for women, or taking medication for low HDL
• high blood pressure—blood pressure level of 130/85 or above, or taking medication for elevated blood pressure
• higher than normal blood glucose levels—fasting blood glucose level of 100 mg/dL or above, or taking medication for elevated blood glucose .

Doctors use blood tests to determine whether a person has prediabetes or diabetes but they do not usually test specifically for insulin resistance. Insulin resistance can be assessed by measuring the level of insulin in the blood.

Once diagnosed, the conditions can be reversed, physical activity and weight loss help the body respond better to insulin.

People can also decrease their risk by eating a healthy diet and reaching and maintaining a healthy weight, increasing physical activity, not smoking and taking medicines prescribed by doctors.