Global estimates indicate that more than half of all adults are either overweight or obese. Obesity carries many health risks because it impairs the body’s immune response and creates a pro-inflammatory environment. In particular, being obese increases the disease severity of influenza infection. A recent study suggests that the impaired immune response commonly exhibited in people who are obese promotes the emergence of more virulent influenza strains.

Influenza is a highly contagious respiratory infection caused by the influenza virus. More than 20,000 people die every year in the United States from influenza-related complications. Many different influenza viruses exist, and they undergo constant change, necessitating regular changes to influenza vaccines. Some of the changes to the influenza virus are due to the health and nutritional status of infected hosts. For example, diet-induced oxidative stress, micronutrient status, and aging can influence influenza virus virulence.

The authors of the study serially infected lean and obese mice with the influenza virus to replicate the spread of influenza within the real-world setting. They found that serial infection of obese mice promoted changes in the virus that produced more virulent strains of the virus. The key driver associated with these changes was an impaired interferon response. Interferons are proteins produced by the body’s cells as a defensive response to viruses. This delayed interferon response also occurred in obesity-derived human bronchial epithelial cells.

These findings suggest that obesity promotes influenza virus diversity and virulence and underscores concerns about the growing obesity problem.

• Link to full study (PDF).