Obesity hurts immune system, according to a new study

The flu puts 114,000 Americans into the hospital every year and kills approximately 36,000. Thus, the rise in obesity is leaving the US more vulnerable to the expected flu pandemic.

• The findings indicate that obesity in humans has a similar effect, said scientists at the University of North Carolina at Chapel Hill School of Medicine.
• Compared to mice of normal weight, which were otherwise identical, obese mice were 10 times as likely to die when infectedwith the flu virus.
• Four percent of lean mice died during the experiments, compared with 40 percent of the extra fat ones, the study showed.
• Presented at an American Society of Nutritional Sciences meeting this weekend in San Diego, California, the study is the first of its kind to examine the effects of obesity on the immune response to infection with influenza.
• In this research, 35 mice fed a high-fat, high-sugar diet for five months grew 37 percent heavier than 35 mice fed a regular rodent diet high in carbohydrates.
• Following influenza infection at five months, which is adulthood for mice, the obese mice demonstrated significantly decreased capacity in every step of the inflammatory immune response in the lungs necessary to stop spread of the virus, Beck said.
• The immune response after infection with influenza virus begins with the production of cytokines whose function is to control the spread of infection and turn on various immune system components, she said.
• There were considerable differences between the obese and lean animals in both gene expression and protein expression of several antiviral and pro-inflammatory cytokines, the researchers said.
• Similarly, someof the pro-inflammatory cytokines, which induce fever, swelling, and recruitment of immune cells, were also significantly lower in obese animals in the early days of infection when they were most needed.
• Another important finding in the obese animals was the reduced ability of natural killer cells, which limit viral replication by killing infected cells and play a central role in the early immune response.