Poor Immune System Response Associated With Obesity

Obese individuals are at higher risk for bacterial infection, and the reason is likely due to poor immune responses. A study was recently conducted at Boston University that more definitively showed the connection between obesity and poor immune response.

Diet Induced Obesity (DIO), as opposed to obesity caused by genetic defects (specifically the leptin gene), was of primary focus in the study. The DIO model was selected for study, says lead author Dr. Salomon Amar, “because most obese individuals suffer from over-nutrition and only a small number of individuals are obese due to mutations in the leptin gene.”

Mice of normal weight and health, and mice with DIO, were subjected to the bacteria Porphyromonas gingivalis, known to be strongly associated with periodontitis (a disease characterized by inflammation of the tissue surrounding the teeth, and suffered by more than 20% of Americans). In previous studies, there have been indications that Porphyromonas gingivalis is also connected to more harmful and life-threatening diseases, such as diabetes and cardiovascular disease.

Past studies have shown a strong correlation between obesity and periodontitis, with the conclusion that “Individuals who maintained a normal weight, pursued regular exercise, and consumed a diet in conformity with the Dietary Guidelines for Americans and the Food Guide Pyramid recommendations were 40% less likely to have periodontitis.”

The recent Boston University study was able to demonstrate that the reason for the obesity-periodontitis correlation is due to the poor immune response in obese individuals to the bacteria Porphyromonas gingivalis,

The mice with DIO had slowed immune response to the bacteria, inhibiting the ability to battle the infection, and had slowed wound-healing mechanisms. Further evidence was that DIO mice “exhibited a 40% increase in bone loss 10 days after the first bacterial inoculation, a time frame consistent with pronounced changes in immune response,” said Dr. Amar.

The DIO mice were also observed to have a much lower white blood cell count than their normal-weight counterparts. White blood cells are the body’s main source of defense against infection, and are responsible for signaling the body’s defense against inflammation caused by periodontitis.

Given the previously shown strong connection between obesity and periodontitis in humans, as well as the general connection between obesity and the decreased ability to battle infection, it’s fair to conclude that the mechanisms observed in the DIO mice would be present in DIO humans as well.

With greater than 30% of Americans classified as obese, and this number predicted to grow, there is extreme importance in better understanding the connection between immune response dysfunction and obesity. While Dr. Salomon Amar, lead investigator of the study, does not claim it to be conclusive, the results are a major step in explaining why obese people have such trouble dealing with infection.

Source: Defeat Diabetes Foundation: Amar, Salomon. Zhou, Qingde. Shaik-Dasthagirisaheb, Yazdani. Leeman, Susan. Proceedings of the National Academy of Sciences. “Diet-induced obesity in mice causes changes in immune responses and bone loss manifested by bacterial challenge.” November 2007.