Type 1 diabetes (T1D) is a chronic autoimmune disease that affects blood sugar levels. While the exact cause is unknown, environmental factors, such as infections, likely play a role.

Diabetes is a group of diseases that can change the way the body manages blood sugar levels. Diabetes can affect the body in one of two ways: The pancreas may not produce enough of the hormone insulin, or the body may not respond effectively to insulin. When this happens, glucose builds up in the bloodstream, raising a person’s blood sugar levels.

Type 1 diabetes (T1D) is a form of the disease in which the immune system mistakenly attacks the cells in the pancreas that produce insulin. While the exact cause is unknown, T1D may result from a combination of a person’s genetics and certain environmental factors.

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Environmental factors are exposures to substances, viruses, other infections, or behaviors that increase a person’s risk of developing a health condition. When an environmental factor directly leads to the development of a health condition such as T1D, it is known as an environmental trigger.

According to a 2022 research review, environmental factors can play a role in triggering T1D or speeding up the disease process. These factors can include viral infections, dietary habits, and changes in gut bacteria.

A 2019 review suggests that, while several viral infections can trigger T1D, the largest amount of evidence relates to a group of viral infections known as enteroviruses. Enteroviruses typically enter the gut as a result of inadequate hygiene or sanitation.

The following types of viral infections can also trigger T1D:

  • Herpesviridae viruses: These viruses can lead to conditions such as chickenpox, shingles, and genital herpes.
  • Parvoviridae viruses: These can cause symptoms such as a facial rash, pain, swelling in the joints, and anemia.
  • Togaviridae: This category of viruses, which includes rubella, can lead to symptoms such as fever, fatigue, headaches, and skin rash.
  • Paramyxoviridae viruses: Measles and mumps fall into this category of viruses, which can lead to symptoms such as fever, cough, congestion, and skin rash.
  • Retroviridae viruses: These viruses can lead to conditions such as arthritis, osteopetrosis, and anemia.
  • Picornaviridae viruses: These can lead to the common cold, conjunctivitis, and inflammation of the heart muscle.
  • Influenza viruses: These viruses can cause the flu.
  • SARS-CoV-2: This virus can lead to coronavirus disease (COVID-19).

The intestinal microbiota, or gut microbiome, is a group of bacteria in the gastrointestinal tract. The role of the intestinal microbiota is to regulate and help maintain the function of the immune system. Changes in the intestinal microbiota can lead to immune system dysfunction and inflammation.

Factors that can change a person’s intestinal microbiota include:

  • the method of childbirth through which they are born
  • the foods they eat
  • medications they take, including antibiotics
  • the pH levels of the water they drink

A 2018 review suggests that there is a close relationship between intestinal microbiota dysfunction and the development of T1D. It is possible that intestinal microbiota dysfunction affects the immune system or that bacteria build up in the intestines and trigger inflammation. The inflamed cells can then travel into the pancreas and trigger T1D.

The hygiene hypothesis is a theory suggesting that children need exposure to bacteria and viruses to build up an immune system response and that, as a result of this exposure, a child may be less likely to develop allergies because their immune system has learned to recognize and fight infections.

A 2021 review suggests that the hygiene hypothesis now extends to the development of autoimmune conditions, including T1D.

There is little evidence to suggest that the foods and drinks a person consumes can lead to T1D. In fact, the Centers for Disease Control and Prevention (CDC) states that diet and lifestyle habits do not cause the condition.

However, a 2021 review suggests that a person’s diet in childhood can affect their risk of developing T1D later in life. The research suggests that breastfeeding and introducing solid foods such as gluten, fruit, and cow’s milk at a later stage can decrease the risk of T1D.

According to a 2023 review, the number of people — particularly children and young people — who have both T1D and obesity is increasing.

A 2022 study suggests that if a person has obesity as a child, they may be more at risk of developing T1D in early adulthood.

Epigenetics is the study of DNA changes that determine whether certain genes are turned on or off. Health experts may also refer to this as gene expression. These changes attach to DNA but do not change its sequence.

Because epigenetic changes help determine gene activity, they influence the production of proteins and how this can affect the body. A 2024 review notes that epigenetic changes may play a role in the development of T1D.

Epigenetics change and develop throughout a person’s life as a result of environmental factors, including aging, infections, diseases, and exposure to toxins such as smoking. These environmental factors interact with the genes a person inherits.

A person may be born with certain genes that put them at a higher risk of developing T1D. However, a 2017 review suggests that epigenetics can determine whether a person with these susceptible genes develops the condition.

Other evidence highlights the role of genetics in the development of T1D. The authors of a 2021 analysis state that more than 200 gene variants may affect a person’s risk of developing the condition.

Currently, the exact cause of T1D is unknown. However, it likely results from a combination of genetics and environmental factors.

Type 1 diabetes (T1D) is an autoimmune disease that can cause high blood sugar levels. Health experts do not yet know the exact cause, but research suggests that environmental factors interact with a person’s genes and can increase the risk of developing T1D.

Environmental factors are any factors beyond a person’s genetics that can contribute to the development of a health condition. Several environmental factors, including viral infections and a person’s diet during childhood, may increase the risk of T1D.