Experiencing a respiratory tract infection by the age of 6 months may raise the risk of type 1 diabetes by the age of 8 years, researchers suggest.

Respiratory tract infections are defined as any infection that affects the sinuses, throat, airways, or lungs, and they are most commonly caused by viruses.

Types of respiratory tract infections include the common cold, flu,tonsillitis, bronchitis, and pneumonia.

Children are particularly susceptible to respiratory tract infections because, unlike adults, their immune system has not acquired the immunity to stave off some of the viruses that cause them.

Respiratory syncytial virus (RSV) is one of the most common causes of respiratory tract infections among children.

The Centers for Disease Control and Prevention (CDC) state that almost all children will have experienced an RSV infection by the age of 2 years, and most children who are hospitalized due to RSV infection are under 6 months of age.

According to study co-author Dr. Anette-Gabriele Ziegler, of Helmholtz Zentrum Munchen in Munich, Germany, and colleagues, previous studies have suggested that viral infections may raise the risk for type 1 diabetes.

They note that more recent studies have also identified a link between respiratory tract infections in the first 6 months of life and greater type 1 diabetes risk.

Type 1 diabetes occurs when the body is unable to produce the hormone insulin, causing a rise in blood glucose levels. It accounts for around 5 percent of all diabetes cases.

First 6 months 'crucial for immune system development'

To investigate the link between early-life respiratory tract infections and type 1 diabetes further, Dr. Ziegler and colleagues analyzed data of 295,420 infants who were born between 2005-2007 in Bavaria, Germany, and who were followed-up for an average of 8.5 years.

During the follow-up period, 720 of the infants were diagnosed with type 1 diabetes, representing a type 1 diabetes incidence of 29 per 100,000 children each year.

Around 93 percent of children experienced at least one infection before the age of 2 years, while 97 percent of children with type 1 diabetes had at least one infection before this age.

Around 87 percent of these infections were respiratory, according to the team, and around 84 percent were viral.

The researchers found that children who experienced respiratory tract infections between birth and 2.9 months of age or between 3 and 5.9 months of age were more likely to be diagnosed with type 1 diabetes by the age of 8 years, compared with children who did not develop respiratory tract infections during those age ranges.

The risk of type 1 diabetes increased further if a child developed a respiratory tract infection during both age intervals, the team found.

Additionally, the researchers found that infants who developed a viral infection between birth and 5.9 months of age were at greater risk for type 1 diabetes by the age of 8 years than those who did not develop a viral infection.

The authors note that they were unable to adjust the results to account for factors that may influence the findings, such as family history of type 1 diabetes among the children or method of birth.

Still, they believe their findings provide further evidence that early viral respiratory tract infections may raise the risk of type 1 diabetes. The authors write:

"It is unknown whether the association with early infections reflects increased exposure to virus or an impairment of the immune system response, perhaps due to genetic susceptibility.

However, the association of respiratory tract infections in the first 6 months with T1D [type 1 diabetes] is consistent with smaller studies assessing autoantibody development, suggesting that the first half-year of life is crucial for the development of the immune system and autoimmunity."