Dr. Janice K. Louie and colleagues at California Department of Public Health in Richmond, California reported in the Feb 11, 2011 issue of Clinical Infectious Diseases that about 50 percent of Californians aged 20 or older who died from swine flu or were hospitalized for the infection in 2009 were obese.

Being obese defined as having a body mass index or BMI of greater than 30 or extremely obese defined as having a BMI of greater than 45 was associated with 200 or 300 percent increased risk of death from swine influenza virus, respectively, the researchers found.
The U.S Center for Disease Control and Prevention views obesity, particularly being morbidly obese as a serious risk factor for death from 2009 pandemic influenza H1N1 virus or swine influenza.
So why does obesity increase risk of death from influenza or flu, in this case, swine flu?
Nutrition researchers in the University of North Carolina at Chapel Hill suggested in the March 15, 2010 issue of the Journal of Immunology that obese individuals are unable to develop protective flu-specific memory T cells.
The memory T cells are generated in the body during the primary infection and they can protect against a secondary infection by targeting internal proteins found in most strains of influenza viruses, according to the researchers.
Erik Karlsson and colleagues conducted an interesting animal study demonstrating how obese mice were vulnerable to influenza viruses, compared with those lean mice.
In the study, Karlsson et al. infected lean and obese mice with a mild influenza virus. And then lean mice were fed a low-fat diet and obese mice a high fat diet. After the mice recovered from this bout of flu, they were infected with a larger dose of a more lethal flu strain.
As a result, all lean mice survived from the second infection while 25 percent of the obese mice died, the researchers reported.
Melinda Beck Ph.D. at UNC who was also the senior author of the current study and colleagues early conducted a similar study in which obese mice and lean mice were subject to a primary flu infection.
As a result, 42 percent of obese mice died while only 5.5 percent of lean mice died from the flu complications.
In practice, doctors see more obese people struggle with influenza than leaner people. Some researchers and doctors theorized that excess adipose tissue constricts lung volume or obesity causes inflammation, which in turn affects the immune response.
(Source: foodconsumer.org)