What causes diabetes?

What happens during diabetes is clear: Too much sugar circulates in the bloodstream. What’s murkier is why some people get diabetes — whether that’s prediabetes, type 1, type 2, or gestational (during pregnancy). Some factors that raise your risk are beyond your control, such as your family history, race, age, and even things like past viral infections or where you live. Fortunately, some other risk factors, like food choices, living with excess weight, or a lack of physical activity, are things you can potentially work to change, reducing your risk. One great resource is WeightWatchers’ Diabetes Plan, which guides you to make healthier food choices that can lead to weight loss and a reduction in A1c.

Read on for the various causes of different types of diabetes, and ways to manage your risks.

How is prediabetes different from regular diabetes?

Prediabetes means your blood sugar is higher than normal, but not high enough for a diabetes diagnosis. A fasting blood sugar level of 100 to 125 mg/dl (milligrams per deciliter) indicates you have prediabetes, while 126 and above indicate diabetes.

The specific cause of prediabetes is not well understood, but genetics, excess weight (especially around the belly), and lack of physical activity play a role. Risk factors are the same as with type 2 diabetes: family history, race, age, living with excess weight or obesity, a lack of activity, and a history of other conditions like high blood pressure, high cholesterol, and cardiovascular disease.

What causes type 1 diabetes?

Type 1 diabetes (T1D) is a lifelong autoimmune disease. It strikes when the body’s immune system attacks and destroys cells in the pancreas that produce insulin, a hormone needed to lower the amount of sugar in your bloodstream. As a result, the body ends up with too little insulin and too much blood sugar.

“Because the immune system destroys these insulin-producing cells in the pancreas, the pancreas can’t produce insulin, which means that patients become dependent on insulin therapy to remain healthy,” says Dr. Tom Donner, M.D., an associate professor of medicine and the director of the Johns Hopkins Diabetes Center.

Type 1 diabetes is largely believed to be the result of genetics and environmental factors that aren’t yet understood. We know people can be genetically predisposed to T1D, but we’re not sure why the disease is triggered in some people with the predisposition and not others, says Dr. Jane Reusch, M.D., a professor of medicine, bioengineering, and biochemistry and the associate director of the Ludeman Family Center for Women’s Health Research at the University of Colorado. That’s what leads many experts to surmise that environmental factors play a part.

Is type 1 diabetes just for kids?

No. Sometimes called “juvenile diabetes,” type 1 diabetes (T1D) was thought to emerge only in childhood, but researchers now know it can develop in people of all ages. In fact, one analysis (which was limited to individuals of white European descent) found that 37% of those living with T1D were diagnosed after age 30.

That said, although T1D can appear at any age, when it does emerge in childhood, it tends to peak at two distinct times: between ages 4 and 7 and between ages 10 and 14.

What raises your risk of type 1 diabetes?

Scientists believe family history (i.e., you have a parent or sibling who has the disease) is the biggest risk factor. According to the American Diabetes Association, if both parents have T1D, a child’s risk is between 10-25% of developing it.

Increasingly, researchers are learning about other potential contributing risk factors for type 1 diabetes, including higher maternal age at birth (defined as over 35), childhood obesity, higher-sugar diets, and viral infections either in utero or very early on in childhood. Geography is also thought to play a role. It’s unclear why, but studies show those living at higher latitudes are more likely to have T1D; Finland consistently reports the highest incidence rate of T1D in the world.

The factors behind type 2 diabetes

Type 2 diabetes (T2D) is the most common form of diabetes, comprising up to 95% of diabetes diagnoses.

Unlike T1D, people with T2D do make some insulin — but their bodies can’t use it properly. People with type 2 diabetes also tend to be insulin-resistant, meaning the body thwarts insulin from doing its job of moving glucose from the bloodstream into cells, providing energy to fuel the body. Because glucose gets stuck in the blood, it causes high blood sugar. This is all coupled with a decreased ability to produce insulin overall.

T2D is caused by a combo of genetics and lifestyle factors, including having excess weight or obesity and a lack of physical activity. Studies show there is a clear link between T2D and obesity, as obesity can cause insulin resistance.

Factors that can contribute to developing T2D include things that you can’t change (your family history, race, age), as well as some things that you can make progress with (having excess weight, your food choices, and not getting enough physical activity). Here’s a closer look at how these factors play a part.

Excess weight

Excess weight (defined as a body mass index of 30 or above) is connected to T2D because when you’re carrying extra pounds, glucose can’t get into cells as easily, which causes insulin resistance — and that’s a proven risk factor for type 2 diabetes.

Where you carry your weight matters, too. Extra body fat, particularly in your belly, can contribute to insulin resistance. Known as visceral fat, this is the type of fat you can’t see because it surrounds internal organs and causes inflammation throughout your body.

A diet high in sugar and fat

A diet that’s high in sugar and saturated fat can lead to excess weight, which can then lead to type 2 diabetes. But these saboteurs can also directly drive up your risk of T2D by negatively impacting insulin. The American Diabetes Association recommends a diet that includes:

• Fruits and vegetables
• Whole grains (like brown rice and whole-grain bread)
• Skinless poultry
• Fish
• Legumes (like lentils and chickpeas)
• Non-tropical vegetable oils (like olive, not coconut)
• Unsalted nuts and seeds

In addition, the American Heart Association offers these guidelines for people with diabetes:

• Reduce salt intake
• Limit red and processed meats
• Limit refined carbohydrates
• Limit sweetened beverages
  
  

Not enough exercise

Working out less than three times a week has been shown to increase your risk of T2D because, according to studies and guidelines from the American Heart Association, at least 150 minutes of exercise per week is needed to help control blood sugar. Remember that exercise counts as any activity that gets you moving: walking, doing chores, keeping up with a small child, etc. When combined with a comprehensive lifestyle change program, 30 minutes of moderate-intensity physical activity daily reduces the risk of developing type 2 diabetes by 58%.

High blood pressure

Also known as hypertension, high blood pressure stresses the heart and tends to co-occur in those with diabetes. Research shows the prevalence of hypertension is two times more likely in people with diabetes. Plus, people with hypertension are more likely to experience insulin resistance, and therefore diabetes as well.

High cholesterol

Low levels of HDL cholesterol — sometimes called good cholesterol — and/or high levels of triglycerides can increase the risks of type 2 diabetes and cardiovascular disease by directly impacting blood sugar levels.

Health disparities and diabetes

Researchers have found that certain racial and ethnic groups and those in a low income bracket face powerful inequities when it comes to social determinants of health, which puts them at a greater risk of developing T2D. For example, according to the Office of Minority Health at the U.S. Department of Health and Human Services, Black adults in the U.S. are 60% more likely than white adults to be diagnosed with diabetes and they are twice as likely to die from the disease.

Why are minority populations more likely to develop diabetes?

There are so many systemic factors at play that make minority groups more prone to diabetes — from genetics to a lack of walkability in neighborhoods that are home to primarily communities of color to decreased access to quality health care and a dearth of healthy food options. This last factor is sometimes referred to as food apartheid, and it’s essentially a lack of agency over the food available within a community and a preponderance of fast food. Ultimately, these forces can lead to having excess weight or obesity, as well as other risk factors for diabetes, says Donner.

Do those factors increase the risk of complications from diabetes too?

Unfortunately, yes. T2D tends to develop at an earlier age in many minority populations, and it’s often less treated, which can lead to other issues. “Complications like kidney disease are more common in racial and ethnic minority patients with diabetes,” Donner says. Why? Because it’s harder to get the right care. Screenings for complications are performed less frequently, due to lower rates of health care coverage and also less support from the health care system, including facing medical racism. When it comes to the prevention and diagnosis of diabetes, white patients receive more access and a higher quality of care than any and all minority groups, according to the National Healthcare Quality and Disparities Report by the U.S. Department of Health and Human Services.

Can where you live affect your diabetes risk?

Our environment profoundly affects our health, and that also applies to diabetes. If you live somewhere without access to safe recreational areas or to healthcare providers, as is the case in rural and urban communities alike, you’re more likely to develop health conditions like diabetes. Plus, says Donner, you will often be diagnosed with diabetes at later stages.

Gestational diabetes during pregnancy

Gestational diabetes is a type of diabetes that is unique to pregnancy, affecting nearly 10% of pregnant people each year. Researchers suspect it develops due to a mix of hormonal and genetic factors.

For starters, the placenta produces hormones like estrogen and cortisol that can block the work of insulin — carrying sugar from the bloodstream to the cells — resulting in insulin resistance.

While pretty much everyone develops a degree of insulin resistance during pregnancy, the pancreas makes up for it in most cases by churning out more and more insulin. When that’s not enough, though, the blood sugar tide rises and rises and gestational diabetes sets in.

Somewhat unsurprisingly, this tends to happen as the placenta grows and its hormone production scales, says Nicole Lynch, a nurse practitioner at the Utah Diabetes & Endocrinology Center at the University of Utah.

The good news is that “once the placenta is delivered, the person does not experience this resistance any longer and the diabetes goes away,” Lynch says.

It’s worth noting, however, that having gestational diabetes does increase your risk of T2D. Nearly half the number of women with gestational diabetes go on to develop T2D later in life. (Though your risk of T2D increases with age regardless of gestational diabetes.)

Risk factors for gestational diabetes

In addition to hormones and genetics, there are some other factors that can make you more susceptible.

• Previous gestational diabetes
  While gestational diabetes disappears after the baby is delivered, it does significantly increase your chances of getting it again during later pregnancies. In fact, studies show someone who has had gestational diabetes is nearly 50% more likely to have it again.

• Having a big baby
  Previously giving birth to a baby weighing more than nine pounds increases the chances of developing gestational diabetes during future pregnancies. This is because delivering a larger baby — known as a macrosomic infant — is a sign of insulin resistance, Lynch says.

• Excess weight or obesity
  Having excess weight or obesity prior to pregnancy can increase your risk of gestational diabetes. Studies show age heightens those risks. The older you are and the higher your pre-pregnancy BMI, the greater your chances of developing the condition.

• An age of 25 years or older
  The older you are, the longer your pancreas has worked, so its ability to keep up with your insulin needs during pregnancy may be diminished.

• Family history of type 2 diabetes
  If a parent or sibling has T2D, you’re predisposed to diabetes, including the gestational kind. Know that predisposition alone isn’t definitive — lifestyle factors can have a major influence.

• Polycystic ovary syndrome (PCOS)
  Polycystic ovary syndrome (PCOS) is a condition where the ovaries produce an abnormal amount of androgens; Women with PCOS often have insulin resistance, according to the CDC. This can spur elevated blood glucose levels that can lead to gestational diabetes, prediabetes, and T2D.

• Socioeconomic status
  Lower-income individuals are more likely to live in under-resourced neighborhoods. Within these communities, social determinants — such as poverty, lack of access to healthy food and safe places to exercise, inadequate employment, and limited educational opportunities — can result in a variety of negative health outcomes, including an increased chance of developing gestational diabetes and T2D.

• Race
  People in marginalized racial and ethnic communities (including African American, Alaska Native, American Indian, Asian American, Hispanic and Latinx, Native Hawaiian, and Pacific Islander) are most affected by gestational diabetes (as well as T2D). Research indicates that this is largely due to decreased access to health-related resources (like medical insurance), increased stress, and lower socioeconomic status more likely impacting under-resourced communities.

The bottom line

While researchers aren’t sure exactly why some people get diabetes and others don’t, there are some factors that make it more likely. Unfortunately, some of those factors you can’t change, such as your family history, race, age, and even things like past viral infections or where you live. But the upside is that there are several important risk factors — like food choices, living with excess weight, or a lack of physical activity — that you can potentially work to change, reducing your risk.