Body Weight
Obesity linked to weakened immunity
By Sue Mueller
Dec 12, 2007 - 9:43:09 PM

WEDNESDAY DEC 12, 2007 (Foodconsumer.org) -- A new animal study showed that obese mice were more likely to get infected with bacteria than lean mice, adding to a growing body of evidence that obesity is linked to a series of health conditions including diabetes as reported early.

A scientist affiliated with foodconsumer.org quickly pointed out that obesity may as well be a sign, but not necessarily the cause of weakened immunity although obesity may have a secondary impact.

The foodconsumer.org scientist cautioned that another possibility is that the animals might use a bad diet which led to both obesity and a weakened immune system.

In the study, researchers in the School of Dental Medicine at the University of Boston Medical Center used a bacterium that causes periodontal disease in both obese mice and lean mice to test how these two groups resist bacterial infections.

They found obese mice had the worse response to the infection and increased their vulnerability to gum disease compared to the lean mice.

In addition, the obese mice had a 40 percent higher rate of alveolar bone loss ten days after they were infected with the bug known as Porphyromonas gingivalis, the study showed.

Previous studies revealed obese people are more likely to suffer from periodontal disease, but the cause remained unknown.  The researchers of the current study provided an explanation why obese mice tend to have a weakened immunity. The key the researchers found is that the production of cytokines in obese mice was altered compared to the lean mice.

Cytokines are compounds that direct immune cells such as T-cells and macrophages to travel to the site of infection, meaning that one part of the immune defense system went wrong in the obese mice.

The researchers also found the levels of the signaling molecules in macrophages from the obese mice were significantly lower and the expression profile of inflammation-related genes was also modified compared to the lean mice.

The researchers suspected that obesity may comprise the immune system through its involvement with a transcription factor NF-kB, which plays a key role in the immune response.

The results of the study were published in the journal, The Proceedings of the National Academy of Sciences.