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Too much body fat makes influenza deadlier

If another really nasty flu virus comes this way, then the regular readers of this webzine will be better prepared. Their healthy fat percentage makes it less likely that they'll succumb to the influenza, according to an animal study that nutritionists at the University of North Carolina published in 2007 in the Journal of Nutrition.

A bad infection
If you are heavily overweight your immune system is compromised. That's probably because layers of fat cannot be thick and healthy at the same time. Thick fat layers are rotting: fat cells that have stored too much fat die, and have to be cleared up by immune cells. That's why there are higher concentrations of inflammatory factors such as IL-6 and TNF-alpha in the blood of obese people.

The researchers wanted to know whether a deregulated immune system makes the body more vulnerable to influenza viruses.

The researchers divided C57BL/6J mice into two groups. One group was given food containing added sugar and fat for a period of 22 weeks. The mice in this group therefore became fat. The other group got normal food and stayed slim.

At the end of the 22 weeks the researchers infected the mice with an aggressive influenza virus.

Ten days after being infected with the flu virus 42 percent of the fattened mice were no longer alive. Of the slim lab mice only 5.5 percent had died. That means that the flu virus was almost seven times more deadly for the fat mice than for the slim ones.

Too much body fat makes influenza deadlier

Three days after infecting them with the influenza virus, the researchers extracted immune cells from the mice's lungs and put them in different concentrations [E:T] in test tubes together with cancer cells. Normally the Natural Killer cells [in this case they were of the CD3-DX5+ type] attack cancer cells, and that's what happened in the test tubes. The figure on the left below shows that the Natural Killer cells destroyed more cancer cells in the slim mice than in the fattened mice.

Too much body fat makes influenza deadlier

A partial explanation for this is shown in the figure on the right above. Three days after being infected with the flu virus there were also fewer Natural Killer cells in the lungs of the fattened mice than in the lungs of the slim mice.

"The importance of the current findings is underscored by the fact that millions of people worldwide are affected by influenza infection every year and the universal prevalence of obesity has reached epidemic proportions", the researchers wrote. "In this study, we found that obesity led to dysregulated innate immune responses to influenza infection and increased mortality."

"Because the innate immune response also activates and polarizes the appropriate cell mediated response, these data indicate that overall immune function may be affected by obesity. Furthermore, these data suggest that, in addition to influenza infection, obesity may increase susceptibility to other viral infections by way of immune system dysregulation."

J Nutr. 2007 May;137(5):1236-43.

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Immune System