Type 2 diabetes mellitus happens when the body can’t use insulin properly — a condition called insulin resistance. Insulin is a hormone made by the pancreas that helps cells take in glucose (sugar) to use as energy. When cells stop responding to insulin, sugar builds up in the blood instead of being absorbed.

At first, the body tries to make more insulin to fix the problem, but over time, the pancreas can’t keep up. This leads to symptoms like high blood sugar (also called hyperglycemia), which can damage nerves, blood vessels, and organs.

According to the American Diabetes Association, both genetic and environmental factors can increase a person’s risk of type 2 diabetes. However, having these risk factors doesn’t mean the person will definitely develop diabetes. Once high blood sugar occurs, people with any form of diabetes are at risk for the same chronic health issues, though they may show up differently for each person.

If you’ve wondered, “How does type 2 diabetes develop?” or “What is the leading cause of type 2 diabetes?” here’s what you should know.

Age

The risk of diabetes increases with age. People aged 35 and older are more likely to develop type 2 diabetes, making diabetes screening more important as you get older. Adults of any age who have a body mass index (BMI) score in the overweight or obese range and have at least one diabetes risk factor should also get screened.

Hereditary Risk Factors

Hereditary risk factors for type 2 diabetes are risk factors you can’t change. They include factors like a 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, siblings, or children who have type 2 diabetes are at higher risk than those with no family history of diabetes.

However, genes alone don’t 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’s difficult to separate genetic factors from other family-related factors, such as shared exercise and eating habits.

Racial or Ethnic Background

According to the American Diabetes Association, certain groups are at higher risk, including:

• American Indians/Alaskan Native adults
• Non-Hispanic Black adults
• Hispanic adults

The reasons for higher risk among these groups aren’t 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

People who have diabetes during pregnancy, called gestational diabetes, or those who give birth to a baby weighing more than 9 pounds, are at a higher risk of getting type 2 diabetes later in life.

Also, those with polycystic ovary syndrome (PCOS) have 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 higher body weight and family history may be contributing factors.

Being diagnosed with metabolic dysfunction-associated steatotic liver disease (MASLD) also increases your risk of developing insulin resistance and type 2 diabetes.

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 having a BMI score in the obese range is linked to type 2 diabetes more than any other factor. Obesity is defined as having a BMI score of 30 or higher. Some research says this accounts for 80 percent to 85 percent of the risk for type 2 diabetes.

Studies show that our genes may affect our body size and how we process energy, which can impact weight. It has been estimated that genetics could explain between 40 percent and 70 percent of a person’s tendency toward higher body weight. Genetics might play a bigger role than we fully understand, so weight may not be something we can completely control. However, diet and lifestyle choices matter, and it’s always necessary to talk to a specialist about your specific situation.

Sometimes people ask, “How does obesity cause type 2 diabetes?” It’s not clear that obesity directly causes type 2 diabetes, but it is a risk factor for the condition. Some scientists believe that abdominal fat releases chemicals that can increase inflammation in the body, making it less sensitive to insulin, but still there is some debate about how this exactly happens.

Another theory suggests that having a higher body weight can change the way the body makes, stores, and uses energy (also called metabolism). These metabolic changes can lead to insulin resistance. Having a larger amount of body fat is also linked to 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 5 percent to 10 percent of one’s body weight can make a difference. However, adopting healthy habits like eating whole foods, quitting smoking, and exercising regularly can also help reduce the risk for type 2 diabetes, regardless of weight. Talk with your doctor about which health-promoting behaviors are best for your needs.

Weight isn't the only risk factor for type 2 diabetes. Many people with BMI scores in the obese range never develop diabetes, and many people with type 2 diabetes aren’t overweight.

Physical Activity

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

About 34 percent of Americans with diabetes don’t get any exercise, and only 24 percent meet the recommended amount of 150 minutes per week. Being active can lower the chance of getting type 2 diabetes by 42 percent. Walking quickly for one hour a day can reduce the risk by 34 percent.

Smoking

Research has shown that smoking is a significant risk factor for type 2 diabetes. In fact, people who quit smoking have a 30 percent to 40 percent lower chance of developing the condition than people who smoke.

Even if you’ve already been diagnosed with type 2 diabetes, stopping smoking could help. It can aid you in keeping type 2 diabetes under control and make it less likely you’ll have to deal with complications. Researchers aren’t exactly sure how this all works yet, but smoking seems to influence how well the body deals with blood sugar levels. People who smoke and have type 2 diabetes have a higher risk of developing peripheral arterial disease (PAD) in the legs or lower extremities. PAD happens when blood vessels that carry blood from the heart to the legs become narrow or blocked.

On DiabetesTeam, members regularly talk about quitting smoking. One shared, “I quit smoking four months ago and that has really helped.” Another said, “Today was day one of no more smoking and taking my illness seriously.”

If you need help to stop smoking, talk to your doctor about medications and support.

Certain Health Conditions

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

Diabetes is also associated with another health condition called atherosclerosis, which is the hardening and narrowing of arteries due to a buildup of plaque (made up of fats, cholesterol, and other substances). Atherosclerosis blocks blood flow and can lead to heart attack or stroke. Low levels of high-density lipoprotein — “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 metabolic dysfunction-associated steatotic liver disease (MASLD) is five times more likely to develop diabetes. It’s important to note that improving MASLD can reduce the risk of diabetes.

MASLD 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 MASLD, but it's thought to be linked to obesity, insulin resistance, high blood sugar, and high levels of fats in the blood.

Alcohol

Can alcohol cause type 2 diabetes? Consuming high amounts of alcohol can cause inflammation in the pancreas, which affects insulin production. Alcohol also contributes sugar and starch to your diet that must either be used or stored as fat. Excessive alcohol use is considered a risk factor for developing type 2 diabetes.

Diet

Have you asked yourself, “What foods cause type 2 diabetes?” or “Does sugar cause type 2 diabetes?” While no single food directly causes type 2 diabetes, diet plays an important role.

One study found that people who drink one or two servings of sugary drinks each day were up to 25 percent more likely to develop type 2 diabetes compared to those who drink little to no sugary drinks. Other studies show that switching from sugary drinks to coffee or tea can lower the risk of diabetes by about 20 percent. Sugary drinks include sodas, sports drinks, energy drinks, sweet tea, and many types of fruit juices.

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

Notice if after eating a meal you crave a sugary snack, chocolate, or other sweets. That could mean you’re developing mild hypoglycemia (low blood sugar) after eating, which may indicate insulin resistance.

One DiabetesTeam member found that changing their diet helped a lot. “Keeping blood sugar levels under 120 naturally by diet. Happier with no meds!” they said. While these results aren’t guaranteed, it can be encouraging to know others have found success managing type 2 diabetes.

Is Type 2 Diabetes Only Caused by Sugar?

Sugar certainly gets a bad rap when it comes to type 2 diabetes, and the research above shows us why. However, it’s important to remember that sugar isn’t the only cause of type 2 diabetes, even though the condition involves high blood sugar levels. Type 2 diabetes can have many causes or even a combination of causes, both genetic and environmental. People with a variety of diets, lifestyles, and body sizes can develop diabetes.

Can Type 2 Diabetes Be Prevented?

According to the Centers for Disease Control and Prevention (CDC), type 2 diabetes can be prevented, or you can at least delay its onset. They suggest making lifestyle changes like shifting your diet, losing a little weight, and adding more physical activity to your routine if you’re at risk for diabetes. Between 5 percent and 10 percent of people with prediabetes develop diabetes each year. So, having prediabetes doesn’t mean you’ll definitely get type 2 diabetes.

The American Diabetes Association offers standards of care, which suggest losing 7 percent of your body weight to prevent or delay the development of type 2 diabetes. The standards also suggest adding 700 calories worth of exercise every week. Activities like brisk walking and strength training contribute to that goal.

Weight loss is not always an appropriate goal for everyone, depending on individual health needs. Together, you and your doctor can determine if your weight is a significant risk factor and you should pursue weight loss to prevent type 2 diabetes. They can help you with support for nutrition and exercise plans, and there are also medications that may help. Some of these are newly on the market, so you’ll want to talk over the pros and cons with your health care provider. They can help you choose the treatment plan that is right for you.

COVID-19 and Type 2 Diabetes

Researchers have found that COVID-19 can increase the risk of developing type 2 diabetes, especially for people with more severe cases. According to a study from The Lancet, people who were hospitalized with COVID-19 were more likely to develop diabetes than those who weren’t. The risk was even higher for patients who had to stay in the intensive care unit (ICU).

The study also found that people who had a low risk of diabetes before getting COVID-19 were more likely to develop it after the infection. Those who were already at a higher risk for diabetes may see their condition progress more quickly after they have COVID-19.

Recent research shows people with diabetes are not only at a higher risk of severe illness from COVID-19 but may also experience serious diabetes-related complications, like diabetic ketoacidosis and insulin resistance. Fortunately, the outcomes for people with diabetes and COVID-19 have improved over time, thanks to better treatments and higher vaccination rates.

Find Your Team

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Are you living with diabetes? Have any of these risk factors influenced your diabetes diagnosis or care? Share your experience in the comments below, or start a conversation by posting on your Activities page.