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What Causes Type 2 Diabetes?

Updated on August 29, 2022
Medically reviewed by
Robert Hurd, M.D.
Article written by
Jane Chung, PharmD, RPh

Type 2 diabetes mellitus, commonly called type 2 diabetes, occurs when cells stop responding to insulin (known as insulin resistance).

Insulin, a hormone produced by the pancreas, allows cells to absorb glucose (sugar) to use as energy. When cells no longer respond to insulin, they cannot absorb glucose properly.

At first, the body makes up for this by producing more insulin. Eventually, the pancreas cannot produce enough insulin to keep up with the body’s needs. This results in glucose staying in the blood and building up, increasing blood sugar levels. Called hyperglycemia, high blood sugar can damage nerves, blood vessels, and organs.

Certain risk factors can contribute to a person’s risk of developing diabetes. However, having these risk factors does not mean the person will definitely develop diabetes.

Research shows that both hereditary (genetic) and environmental factors can influence a person’s risk of type 2 diabetes. Experts believe diabetes is most likely caused by a combination of these factors.

Age

The risk of diabetes increases with age. People aged 35 and older are more likely to develop type 2 diabetes, although children and younger adults can also be at risk.

Hereditary Risk Factors

Hereditary risk factors are considered nonmodifiable risk factors, meaning they cannot be changed. They include factors like family history of certain health conditions or your racial or ethnic heritage.

Family History

Family history may play a role in developing diabetes. People with parents or siblings who have type 2 diabetes are at higher risk than those with no family history.

However, genes alone do not determine diabetes risk. A great example is identical twins — if one twin develops type 2 diabetes, the other twin has, at most, a 75 percent chance of developing it as well. It is difficult to separate genetic factors from other family-related factors such as shared exercise and eating habits.

Race or Ethnic Background

According to the National Institute of Diabetes and Digestive and Kidney Diseases, certain groups are at higher risk, including:

  • African Americans
  • Alaska Natives
  • Asian Americans
  • Hispanics/Latinos
  • Native Americans
  • Native Hawaiians
  • Pacific Islanders

The reasons for higher risk among these groups are not fully understood. Social factors like income, access to health insurance and health care, risk factors for obesity, meal and exercise choices, and genetics are all possible reasons for the difference.

Health Conditions

Individuals who have gestational diabetes during pregnancy or those who give birth to a baby weighing more than 9 pounds are at an increased risk of developing type 2 diabetes later on.

Those with polycystic ovary syndrome (PCOS) are at an increased risk for type 2 diabetes. This is because people with PCOS are often insulin-resistant. The exact causes of PCOS are unknown, but excess weight and family history may be contributing factors.

Environmental Risk Factors

Environmental risk factors include weight, exercise, and other lifestyle choices. These can be changed, so they are considered modifiable risk factors.

Weight

Research suggests that obesity promotes diabetes more than any other factor, accounting for 80 percent to 85 percent of the risk for type 2 diabetes. Obesity is defined as having a body mass index (BMI) or 30 or higher.

Scientists believe that abdominal fat releases chemicals that can increase inflammation in the body, making it less sensitive to insulin.

Another theory suggests that obesity can change the way the body makes, stores, and uses energy (also called metabolism). These metabolic changes can lead to insulin resistance. Obesity may also cause prediabetes, which can become type 2 diabetes.

According to the American Diabetes Association, weight loss can help prevent and manage type 2 diabetes. Even losing 10 to 15 pounds (or losing 5 percent to 10 percent of one’s body weight) can make a big difference.

Weight is not the only risk factor for type 2 diabetes. Many people with obesity never develop diabetes, and many people with type 2 diabetes are not overweight or only moderately overweight.

Physical Activity

Low physical activity may promote insulin resistance, thus increasing your risk of developing diabetes. On the other hand, physical activity increases insulin sensitivity — how responsive cells are to insulin. Exercise can also lower blood glucose.

One study showed that daily exercise — 30 minutes per day of walking or other moderately intense activity — can reduce the risk of developing type 2 diabetes by 58 percent.

Diet

Diet plays an important role in type 2 diabetes. One study found that people who drink one or two servings of sugary drinks each day were 26 percent more likely to develop type 2 diabetes compared to those who drink little to no sugary drinks. These beverage include sodas, sports drinks, energy drinks, sweet tea, and many types of fruit juices.

Few studies have found a strong link between type 2 diabetes and consuming large amounts of carbohydrates and fats. On the other hand, many studies show that diets high in sugars are associated with an increased risk of developing type 2 diabetes.

Meals consumed at regular times with low fat and high fiber, including a limited amount of carbohydrates, are recommended by nutritionists. Work with your diabetes care team to develop a balanced meal plan that works for you.

Certain Conditions

When left untreated, hypertension (high blood pressure) has been linked to diabetes complications (negative effects of a condition). The American Heart Association recommends that people with diabetes maintain a blood pressure of less than 130/80 mmHg (which stands for millimeters of mercury).

Diabetes is also associated with atherosclerosis, which is the hardening and narrowing of arteries due to a buildup of plaque (made of fats, cholesterol, and other substances). Atherosclerosis blocks blood flow and can lead to heart attack or stroke. Low levels of high-density lipoprotein (HDL) — “good” cholesterol — or high levels of triglycerides increase the risk for type 2 diabetes and cardiovascular (heart and blood vessel) disease. Abnormal cholesterol levels can be controlled through a healthy diet and exercise.

According to the journal Metabolism, a person with nonalcoholic fatty liver disease (NAFLD) is five times more likely to develop diabetes. It’s important to note that improving NAFLD can reduce the risk of diabetes. NAFLD is a term used to describe a range of liver conditions affecting people who drink little to no alcohol. The condition causes too much fat to be stored in liver cells. Health experts aren’t sure what causes NAFLD, but it is thought to be linked to obesity, insulin resistance, high blood sugar, and high levels of fats in the blood.

Alcohol

Consuming high amounts of alcohol can cause inflammation in the pancreas, affecting insulin production. Alcohol contributes sugar and starch to your diet that must either be used or stored as fat.

COVID-19 and Type 2 Diabetes

Researchers have been studying the long-term effects of COVID-19.

A study from The Lancet found that people with COVID-19 were at an increased risk of developing diabetes.

In addition, the researchers found that these risks increased with the severity of COVID-19. Compared to people who were not hospitalized for COVID-19, people who were hospitalized were at a higher risk of diabetes. People who were in the intensive care unit for COVID-19 were at an even higher risk of diabetes.

The study also suggests that people who were at low risk of diabetes before exposure to COVID-19 were at an increased risk after COVID-19 infection, compared to people who never had COVID-19. Also, in people who were already at high risk of diabetes, COVID-19 may intensify those risks and speed up the occurrence of diabetes.

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References
  1. Type 2 Diabetes — Cleveland Clinic
  2. Diabetes Treatment: Using Insulin To Manage Blood Sugar — Mayo Clinic
  3. Diabetes Risk Factors — Centers for Disease Control and Prevention
  4. Symptoms & Causes of Diabetes — National Institute of Diabetes and Digestive and Kidney Diseases
  5. What’s Race Got To Do With Diabetes? — AARP
  6. Fighting Diabetes’ Deadly Impact on Minorities — U.S. Food and Drug Administration
  7. Diabetes — Mayo Clinic
  8. Risk Factors for Diabetes — National Institute of Diabetes and Digestive and Kidney Diseases
  9. Family Health History and Diabetes — Centers for Disease Control and Prevention
  10. Learn the Genetics of Diabetes — American Diabetes Association
  11. PCOS (Polycystic Ovary Syndrome) and Diabetes — Centers for Disease Control and Prevention
  12. Diabetes and Obesity — Diabetes.co.uk
  13. Extra Weight, Extra Risk — American Diabetes Association
  14. Myths About Diabetes — American Diabetes Association
  15. Diabetes Mellitus and Exercise — StatPearls
  16. Exercise and Diet Reduce Risk of Diabetes, US Study Shows — BMJ
  17. Sugary Drinks — Harvard T.H. Chan School of Public Health
  18. Effect of Diet on Type 2 Diabetes Mellitus: A Review — International Journal of Health Sciences
  19. Diabetes Risk Factors — American Heart Association
  20. Nonalcoholic Fatty Liver Disease — Mayo Clinic
  21. Non-Alcoholic Fatty Liver Disease and Diabetes — Metabolism
  22. Risks and Burdens of Incident Diabetes in Long COVID: A Cohort Study — The Lancet Diabetes & Endocrinology
  23. Sugar-Sweetened Beverages and Risk of Metabolic Syndrome and Type 2 Diabetes: A Meta-Analysis — Diabetes Care

All updates must be accompanied by text or a picture.
Robert Hurd, M.D. is a professor of endocrinology and health care ethics at Xavier University. Review provided by VeriMed Healthcare Network. Learn more about him here.
Jane Chung, PharmD, RPh earned a Bachelor of Science in Pharmacy Studies and a Doctor of Pharmacy from Northeastern University in Boston, MA. Learn more about her here.

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