Not everyone with type 2 diabetes is overweight, but obesity and an inactive lifestyle are two of the most common causes of type 2 diabetes. These things are responsible for about 90%-95% of diabetes cases in the U.S.
What Causes Type 2 Diabetes?
When you're healthy, your pancreas (an organ behind your stomach) releases insulin to help your body store and use sugar from the food you eat. Diabetes happens when one or more of the following happens:
- Your pancreas doesn't make any insulin.
- Your pancreas makes very little insulin.
- Your body doesn’t respond to insulin the way it should.
Unlike people with type 1 diabetes, people with type 2 diabetes do make insulin. But the insulin their pancreas releases isn’t enough, or their body can't recognize and use the insulin properly. (Doctors call this insulin resistance.)
When there isn't enough insulin or it isn't used as it should be, glucose (a type of sugar) can't enter your cells. It builds up in your bloodstream instead. This can damage many areas of the body. Also, because cells aren't getting the glucose they need, they don't work the way they should.
Weight and diabetes
When you're overweight, you're at a higher risk for type 2 diabetes. This is especially true if your extra weight is in your belly. Extra weight leads to insulin resistance and dysfunction of specific cells in your body.
One measure of obesity is body mass index (BMI), which estimates body fat based on weight and height. For men and those assigned male at birth who are older than 18, the lifetime risk of getting type 2 diabetes with a BMI of 18.5 or lower is 7%. The risk increases as your BMI increases. If your BMI is higher than 35, your risk of type 2 diabetes is 70%. For women and those assigned female at birth who are older than 18, the diabetes risk at 18.5 BMI is 12%, which grows to 74% with a BMI of 35 or greater.
Losing 5%-10% of your overall body weight can improve your odds.
Diet and diabetes
Everything you eat affects your blood sugar levels. But foods that are high in simple carbohydrates, fat, and calories have a significant impact. Studies have found that eating lots of red meat, sweets, and fried food can lead to insulin resistance. Eating too much of these foods also contributes to weight gain, which increases your chances of diabetes.
Diabetes and metabolic syndrome
When you have metabolic syndrome, you have a set of risk factors that are linked to heart disease, diabetes, and stroke. Those things include:
- Extra weight that you carry in your belly. One measure of this is your waist size. Anything above 35 inches (for women) and 40 inches (for men) is a risk factor.
- High blood pressure
- High triglyceride levels
- Low levels of LDL, or "good" cholesterol
- Impaired fasting blood glucose readings
Most people with metabolic syndrome have insulin resistance.
Diabetes and PCOS
When you have polycystic ovary syndrome (PCOS), small cysts develop on your ovaries. Experts aren't really sure what causes PCOS, but weight and genes may play a role. Many people with PCOS have insulin resistance, which puts them at a higher risk for type 2 diabetes.
Medications causing diabetes
Some medicines you take for other conditions can make your blood sugar spike. The types of drugs linked to diabetes include:
- Steroids
- Antipsychotic drugs
- Antiretrovirals
- Some chemotherapy drugs
- Immunosuppressants taken after transplants
- Thiazide diuretics
- Niacin and statins taken to lower cholesterol
- Beta-blockers
Gestational diabetes
This is a type of diabetes that begins when you're pregnant. Experts aren't exactly sure what causes it, though excess weight can play a role. The hormonal changes in your body during pregnancy may make it harder for your body to regulate your blood sugar. Usually, your blood sugar will return to normal once you've given birth. But gestational diabetes does raise your risk of having type 2 diabetes in the future. Your baby also has a higher risk of type 2 diabetes in the future.
Smoking and diabetes
If you smoke cigarettes, you're 30%-40% more likely to develop diabetes than a nonsmoker. The more you smoke, the more your risk increases. And when you have type 2 diabetes, smoking can make it harder to manage your condition and get your insulin dose right.
Sleep and diabetes
Sleep problems are associated with diabetes. If you don't get enough sleep, your body may not be sensitive enough to insulin. Disrupted sleep also can interfere with the hormones that control your body's glucose. One common sleep problem is sleep apnea, which is linked to obesity, another factor in diabetes. Diabetes itself can disturb your sleep -- for instance, if you have diabetes you may wake up often during the night to get a drink or pee.
Type 2 Diabetes Risk Factors
Many things can add to the risk of type 2 diabetes.
Diabetes and family history
Type 2 diabetes is believed to have a strong genetic link, meaning that it tends to run in families. If you have a parent, brother, or sister who has it, your chances are higher. Several genes may be related to type 2 diabetes.
Health conditions related to diabetes
If you have any of these conditions, you may want to ask your doctor about a diabetes test:
- High blood pressure
- High triglyceride levels (it's too high if it's over 500 milligrams per deciliter (mg/dL))
- Low HDL cholesterol level (it's too low if it's less than 40 mg/dL for men and less than 50 mg/dL for women)
- Gestational diabetes or giving birth to a baby weighing more than 9 pounds
- Prediabetes (when your blood sugar level is above normal, but you don't have the disease yet)
- Heart disease
- Obesity or being overweight. Research shows this is a top reason for type 2 diabetes. Because of the rise in obesity among U.S. children, this type is affecting more teenagers.
- Polycystic ovary syndrome (PCOS)
- You’ve had an organ transplant. After an organ transplant, you need to take drugs for the rest of your life so your body doesn’t reject the donor organ. These drugs help organ transplants succeed, but many of them, such as tacrolimus (Astagraf, Prograf) or steroids, can cause diabetes or make it worse.
- Impaired glucose tolerance. Prediabetes is a milder form of this condition. It can be diagnosed with a simple blood test. If you have it, there’s a strong chance you’ll get type 2 diabetes.
Diabetes and race
African Americans, Native Americans, Hispanic Americans, and Asian Americans are more likely to get type 2 diabetes than non-Hispanic whites.
Diabetes and alcohol
Drinking a lot of alcohol is linked to diabetes, though the relationship isn't entirely clear. Among other things, heavy drinking might cause you to gain weight, which is a risk factor for diabetes.
LGBTQ and diabetes risk
If you're lesbian, gay, bisexual, transgender, or queer, you have an increased risk of developing type 2 diabetes. The reasons are complicated. Lesbian and bisexual women and transgender men are more likely to be overweight, a risk factor for diabetes. Studies suggest LGBTQ people may have more disrupted sleep, another factor that contributes to diabetes risk. Extra weight and disrupted sleep are both linked to long-term stress, and studies have found that LGBTQ people have extra stress in their lives because of their minority status. Other health conditions that may be more prevalent among LGBTQ people include HIV, PCOS, high blood pressure, heart disease, and kidney disease. All of these conditions can raise your diabetes risk.
Diabetes and age
The risk of type 2 diabetes begins to rise significantly around age 45 and rises considerably after age 65.
Other risk factors
Lifestyle issues can play a role in your diabetes risk. If you're not physically active, your risk goes up. Your risk also is increased if your diet is high in fat and simple carbohydrates. That can be the result of where you live and lack of access to healthy food.
A proper diet and healthy lifestyle habits, along with medication, can help you manage type 2 diabetes the same way you manage other areas of your life. Be sure to seek the latest information on this condition as you become your own health advocate.
The Role of Insulin in Type 2 Diabetes
To understand why insulin is important, it helps to know more about how your body uses food for energy. Your body is made up of millions of cells. To make energy, these cells need food in a very simple form. When you eat or drink, much of the food is broken down into a simple sugar called glucose. It moves through your bloodstream to these cells, where it provides the energy your body needs for daily activities.
Insulin and other hormones control the amount of glucose in your bloodstream. Your pancreas is always releasing small amounts of insulin. When the amount of glucose in your blood rises to a certain level, the pancreas will release more insulin to push more glucose into the cells. This causes the glucose levels in the blood (blood glucose levels) to drop.
To keep blood glucose levels from getting too low (hypoglycemia, or low blood sugar), your body signals you to eat and releases some glucose from the stores kept in the liver. It also tells the body to release less insulin.
People with diabetes either don't make insulin or their body's cells can no longer use their insulin. This leads to high blood sugar. By definition, diabetes is:
- A blood glucose level greater than or equal to 126 milligrams per deciliter (mg/dL) of blood after an 8-hour fast
- A non-fasting glucose level greater than or equal to 200 mg/dL, along with symptoms of diabetes
- A glucose level greater than or equal to 200 mg/dL on a 2-hour glucose tolerance test
- A1c greater than or equal to 6.5%. Unless the person is having obvious symptoms of diabetes or is in a diabetic crisis, the diagnosis must be confirmed with a repeat test.
Takeaways
When you have type 2 diabetes, your body doesn't make enough insulin, or it can't use the insulin it makes correctly. That causes glucose to build up in your blood, something that's called high blood sugar. The main causes of type 2 diabetes are obesity and an inactive lifestyle. But other conditions and even medicines you take can play a role. Many things can increase your risk of diabetes, including your family history, race, and age.
What Causes Type 2 Diabetes FAQs
What are the major risk factors for type 2 diabetes?
Many things can increase your risk of diabetes, including your genes, age, and certain health conditions. Those include high blood pressure, high triglycerides, and low levels of LDL or "good" cholesterol.
What are the causes of type 2 diabetes?
The two main causes of type 2 diabetes are carrying excess weight -- especially in your belly -- and not getting enough exercise.
