Researchers from the University of National Institutes of Health found immune cells located in the body fat of mice, which have the ability to “remember” previous exposure to infections, viruses, and other pathogens. If you are exposed to the same pathogen in the future, these memory T cells could help the body to trigger an appropriate immune response.

While it’s necessary to have some degree of body fat to encourage this process to take place, being overweight can have negative effects on immunity.

Fat cells can emit cytokines, which contribute to levels of inflammation in the body. Cytokines are proteins that are produced by cells, including immune cells. Under normal circumstances, they work with the immune system to regulate the immune response and maintain “normal” cellular activity.

The inflammation associated with obesity may be a factor in your immune system being on “high alert” most or all of the time. This can fool the immune system to act when it doesn’t need to, which disrupts the delicate balance between fighting pathogens and not treating non-pathogens as foreign threats.

Since obesity has been characterized by researchers as a state of low-grade chronic inflammation, excess cytokine production can be problematic for immunity. The more fat cells you have in your body, the greater the potential for cytokines and inflammation.

This can have implications for many health conditions, including flu.

Research published in the Journal of Infectious Diseases indicated that obese people who develop symptoms of influenza A may continue to shed for longer than their slimmer counterparts.

During the H1N1 flu pandemic, obese patients were more likely to die from complications, particularly if their BMI scored above 30.

Being overweight can be a significant risk factor for developing more serious health problems too.

Researchers in Canada have found strong links between obesity and being hospitalized for respiratory conditions. Their findings led them to conclude that an immune response may be triggered for obese patients.

Obesity-related inflammation can also be a factor in heart disease. The cytokines produced by fat cells can damage the arteries and raise blood pressure.

If the body produces too many cytokines, it can also lead to autoimmune conditions. An overproduction of interleukins can be present in conditions such as rheumatoid arthritis, according to research published in Microbiology and Molecular Biology Reviews.