What Causes Type 2 Diabetes?

Close up of person testing blood sugar levels

filadendron / Getty Images

Diabetes is a common disease affecting 425 million adults worldwide. That number is expected to rise to 592 million by 2035. It’s a chronic disease that causes hyperglycemia (high blood sugar levels).

Type 2 diabetes is the most common type of diabetes. Risk factors are both genetic and environmental. The main cause of type 2 diabetes is insulin resistance.

Cause

Your body converts food to glucose (sugar) and uses it for energy. Insulin, a hormone made in the pancreas, tells your body how much sugar to release into the bloodstream.

Diabetes occurs when you don’t have enough insulin or your body doesn’t use insulin properly. This causes too much sugar to stay in the bloodstream, resulting in persistent hyperglycemia (high blood sugar)

Long-term exposure to this extra sugar negatively affects how your body makes, delivers, and uses insulin. This results in insulin resistance, the main cause of type 2 diabetes.

Is Type 2 Diabetes Hereditary? 

Your genetic makeup refers to your genes or DNA (deoxyribonucleic acid). Genetic disorders are characterized by gene mutations or a change or difference in your DNA sequence. However, this doesn’t always mean that genetic mutations are inherited.

When you inherit a genetic mutation, it’s present at birth. But genes can also mutate or change based on environmental factors. Genes that mutate after birth are not inherited.

Your chance of getting type 2 diabetes increases when you have a first-degree relative who has it. First-degree relatives are your siblings, parents, and children.

One study noted the following statistics regarding family connections:

  • If you have one sibling with type 2 diabetes, your risk increases by 2-3%.
  • If you have two siblings with type 2 diabetes, your risk increases by 30%.
  • The risk is higher if the parent who has it is your mom rather than your dad.

Researchers have identified 150 genetic variations that may increase the risk of diabetes. How these mutations contribute to the disease is still unknown. Most likely, a combination of hereditary and environmental factors causes type 2 diabetes.

Do these statistics mean you inherit type 2 diabetes? Not necessarily. They just show a family connection and a possible genetic predisposition to the disease. Shared lifestyles may also contribute to the family link.

Who Gets Type 2 Diabetes? 

Type 2 diabetes is a global epidemic that affects people all across the world. But, some people are more likely to develop type 2 diabetes based on certain factors.

  • Location: Eighty percent of people with type 2 diabetes live in low and middle-income countries. Rates are also rising in Western Europe and island states in the Pacific.
  • Weight: Obesity is one of the top risk factors for type 2 diabetes. 
  • Age: Type 2 diabetes is typically seen in adults over 45. But, it can also affect children, teens, and young adults. 
  • Pre-existing conditions: Type 2 diabetes is more likely if you have specific pre-existing health conditions such as prediabetes or high blood pressure.

Type 2 diabetes is more common in those who are Asian American, African American, Hispanic/Latino, Pacific Islander, or American Indian.

Risk Factors 

Risk factors for type 2 diabetes include things you can’t change, like genetics and age. Other risks are behavioral, meaning you have more or more control over them. Those include physical inactivity or poor nutrition.

Obesity

Obesity is the greatest risk factor for type 2 diabetes. This is because adipose (fat) tissue promotes insulin resistance. It increases your risk by six times, regardless of your genetic predisposition to the disease.

Having a higher percentage of body fat alone is a risk factor. But, studies show that those with less muscle mass, excess abdominal fat, and a bigger waist circumference are most at risk. 

For those assigned male at birth, a waist circumference over 40 inches increases your risk. For those assigned female at birth, the risk increases if your waist is 35 inches or more (when not pregnant). 

Physical Inactivity

Physical inactivity increases your chance of gaining weight, causing insulin resistance. Some insulin resistance is normal with age, but physical inactivity and excessive weight gain make it worse.

Interestingly, lack of exercise increases your risk regardless of your weight. Type 2 diabetes rates are rising in countries with lower overall obesity. Researchers say this is from their decreased activity and changes in food habits.

Poor Diet or Nutrition

Excessive calories, sugary foods and drinks, saturated fats, and trans fats lead to obesity. Consistent exposure to glucose and free fatty acids affects insulin secretion, leading to insulin resistance.

Poor nutrition can start in early life as well as adulthood. Researchers have found that a higher intake of green leafy vegetables and whole grains decreases your risk of type 2 diabetes. 

Lowering your intake of the following foods also reduces your risk of type 2 diabetes:

  • Refined grains such as white bread, white rice, and corn
  • Red and processed meat
  • Sugar-sweetened beverages such as soda and juice

Age

Type 2 diabetes can occur at any age, but most commonly begins in middle age (over 45) or later. About 25% of people with type 2 diabetes are 65 years or older.

Genetics

Your risk of diabetes increases when you have a first-degree relative with diabetes. This includes siblings and parents. It’s unclear whether this is due to shared genetics or lifestyles. Most likely, it’s a combination of both.

Medical History

Certain health conditions make it more likely that you may get diabetes. This includes insulin resistance and prediabetes. Prediabetes is when your blood sugar levels are high but not high enough for you to receive a type 2 diabetes diagnosis.

In the U.S., 96 million adults (one-third of the population) have prediabetes. Researchers believe that 8 out of 10 of them are unaware. 

Other health conditions that increase your risk include:

  • Hypertension (high blood pressure)
  • Dyslipidemia (imbalance of lipids such as cholesterol in the blood)
  • Hypertriglyceridemia (increased triglycerides—a type of fat—in your blood)
  • Polycystic ovarian syndrome, or PCOS (a hormonal condition causing enlarged ovaries with cysts)
  • Acanthosis nigricans (hyperpigmentation or darker areas in the folds of the body), which is associated with insulin resistance
  • Gestational diabetes (a form of diabetes that occurs during pregnancy)
  • Atherosclerotic cardiovascular disease (build-up of fats and cholesterol in the blood vessels)

Behavioral Risk Factors

In addition to lack of exercise and poor diet, the following habits increase your risk of type 2 diabetes:

  • Sleeping fewer than five hours a night
  • Sleeping more than nine hours a night
  • Working on a rotating shift
  • Smoking cigarettes (independent of weight or other risk factors)
  • Consuming a moderate amount of alcohol 

Experts say 90% of type 2 diabetes is preventable through decreasing behavioral risk factors. This includes keeping a healthy weight, eating a healthy diet, getting 30 minutes of exercise per day, avoiding smoking, and reducing alcohol intake.

A Quick Review 

Type 2 diabetes is a chronic health condition characterized by high blood sugar levels. The most common cause of type 2 diabetes is insulin resistance due to a combination of environmental and genetic factors.

Insulin is a hormone released by the pancreas. It helps the body regulate glucose (blood) sugar that stays in the bloodstream. When your body doesn’t use insulin properly (insulin resistance), too much sugar stays in the blood.

While type 2 diabetes can occur at any age, it’s most common in adults over 45. Obesity, poor nutrition, and decreased activity are a few of the main risk factors. While there is a family connection, the exact reason for the link is still unknown.

Was this page helpful?
Sources
Health.com uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. DeFronzo R, Ferrannini E, Groop L, et al. Type 2 diabetes mellitus. Nat Rev Dis Primers. 2015;1:15039. doi:10.1038/nrdp.2015.39

  2. Goyal R, Jialal I. Diabetes mellitus type 2. In: StatPearls. Treasure Island (FL): StatPearls Publishing; 2022.

  3. American Diabetes Association. Type 2 diabetes: Life doesn’t end with type 2 diabetes.

  4. National Library of Medicine. Type 2 diabetes.

  5. Schnurr TM, Jakupović H, Carrasquilla GD et al. Obesity, unfavourable lifestyle and genetic risk of type 2 diabetes: A case-cohort study. Diabetologia. 63:1324–1332 (2020). doi:10.1007/s00125-020-05140-5

  6. Khan MAB, Hashim MJ, King JK, Govender RD, Mustafa H, Al Kaabi J. Epidemiology of type 2 diabetes - global burden of disease and forecasted trends. J Epidemiol Glob Health. 2020;10(1):107-111. doi:10.2991/jegh.k.191028.001

  7. Centers for Disease Control and Prevention. Type 2 diabetes.

  8. National Institute of Diabetes and Digestive and Kidney Diseases. Type 2 diabetes.

  9. Centers for Disease Control and Prevention. Diabetes fast facts.

Related Articles