In addition, certain lifestyle factors can cause type 2 diabetes in individuals with no known family history.
This complex interaction between genes, lifestyle, and environment points to the importance of taking steps to minimize individual diabetes risk.
Is type 1 diabetes hereditary?
Type 1 diabetes is a chronic autoimmune disease and is usually diagnosed during childhood.
Type 1 diabetes is an autoimmune disease, which means that it causes the body's immune system to attack healthy cells. It is often called juvenile diabetes because most people are diagnosed in childhood, and the condition then lasts their lifetime.
Doctors used to think type 1 diabetes was wholly genetic. Newer studies have shown, however, that children develop type 1 diabetes 3 percent of the time if their mother has the condition, 5 percent of the time if their father has it, or 8 percent if a sibling has type 1 diabetes.
Consequently, researchers now believe that something in the environment has to trigger type 1 diabetes.
Some risk factors include:
- Cold weather. People develop type 1 diabetes in winter more frequently than summer. It is also more common in places with cool climates.
- Viruses. Researchers think some viruses might activate type 1 diabetes in people who are otherwise vulnerable. Measles, mumps, coxsackie B virus, and rotavirus have been linked to type 1 diabetes.
Research suggests that people who develop type 1 diabetes may have autoimmune antibodies in their blood for many years before showing symptoms. As a result, the disease may develop over time, or something may have to activate the autoimmune antibodies for symptoms to appear.
Is type 2 diabetes hereditary?
The risk of type 2 diabetes is greatly increased by the combination of obesity and a family history of diabetes.
Type 2 diabetes is the more common form of the disorder, accounting for 90 percent of cases worldwide. Similarly to type 1 diabetes, type 2 diabetes is at least partially hereditary. People with a family history of the disorder are significantly more likely to develop diabetes.
Type 2 diabetes is also linked to a number of lifestyle factors, including obesity. In one study, researchers found that 73 percent of people with type 2 diabetes had moderate to high family risk factors, while just 40 percent were obese. This finding suggests that genetics may increase the risk of developing diabetes even more than obesity, at least in this study group.
When obesity and family history were both present, however, the risk of diabetes significantly increased. Overall, people who reported obesity and had a family history of diabetes had a 40 percent risk of developing type 2 diabetes.
This does not mean that type 2 diabetes is purely hereditary. Neither does it mean that a genetic risk factor means developing the disease is unavoidable.
Some lifestyle factors that can make a genetic risk factor worse, or can lead to type 2 diabetes in people with no family history, include:
- Being overweight or obese. In addition, for some people of Asian descent, a body mass index (BMI) of 23 or higher is a risk factor, even though this is not considered overweight.
- Being sedentary. Exercise can help lower blood glucose.
- Having high blood pressure, high levels of fats, called triglycerides, that are in the blood, or low HDL, so-called "good" cholesterol. A history of cardiovascular disease also increases the risk.
- A history of gestational diabetes.
- Having depression or polycystic ovarian syndrome.
The risk of type 2 diabetes increases with advancing age, such that people over the age of 45 are at a heightened risk, particularly if they have other risk factors.
It can be difficult to work out whether a family history of diabetes is genetic, due to lifestyle factors, or a combination of the two. This is because behavior also tends to run in families.
For example, many families eat meals together, so parents may influence their children's eating habits, weight, and their risk of diabetes. A family that eats large quantities of high-fat, high-sugar foods may also have a history of diabetes. This could be because family members are overweight due to unhealthy diets, because of a genetic risk for diabetes, or both reasons.
It is not always possible to work out why one person gets diabetes and another does not. That does not mean that diabetes is inevitable, even in people with significant family histories. And because most research points to the role of lifestyle and environment, even people with no family history of diabetes may be prone to the disease with enough lifestyle risk factors.
Reducing the risk of passing on diabetes
There are many strategies for reducing the risk of type 2 diabetes, including maintaining a physically active lifestyle.
Researchers have not mapped all the genetic risk factors for diabetes. However, the study mentioned above suggests that people who know that they are at a heightened risk for diabetes may take steps to reduce their risk.
Parents concerned that their children might develop type 1 diabetes should breast-feed them. The American Academy of Pediatrics advise exclusive breast-feeding until 6 months, so parents should introduce solids between 6 and 7 months.
People concerned about their risk of diabetes may wish to discuss that risk with doctors or undergo genetic testing, since research suggests that knowledge of risk can encourage people to make healthier lifestyle choices.
If someone does not have any known risk factors for type 2 diabetes, it does not mean that they will never get diabetes, however.
Many of the same lifestyle choices that help people with diabetes manage their symptoms can also reduce the risk of diabetes, particularly type 2 diabetes. Those strategies include:
- Maintaining a healthy body weight. People who are overweight or obese may reduce their risk of diabetes by losing as little as 5 to 7 percent of their starting weight, even if they remain overweight or obese.
- Keeping physically active. People should get at least 30 minutes of exercise at least 5 days per week.
- Eating healthful balanced meals. Several small meals can support feelings of fullness and reduce the risk of overeating. Fiber can lower blood glucose, so people should choose fiber-rich foods such as fruits, vegetables, and whole grains.
People at high risk of diabetes may benefit from routine blood glucose monitoring. Symptoms of diabetes, such as excessive thirst or urination, exhaustion, and frequent unexplained infections, always warrant medical attention. However, most people with diabetes have no symptoms to begin with.