Influence of Obesity on Pneumococcus Infection Risk in the Elderly

Abstract

Obesity negatively affects immune function and host defense mechanisms. Obesity is associated with chronic activation of the innate immune system and consequent local and systemic inflammation which contribute to pathologic conditions such as type-2 diabetes mellitus, cancer, psoriasis, atherosclerosis, and inflammatory bowel disease. Individuals with obesity have increased susceptibility to contract viral, bacterial, and fungal infections and respond sub-optimally to vaccination. In this review, we summarize research findings on the effects of obesity on immune responses to respiratory tract infections (RTI), focusing on Streptococcus pneumoniae ("pneumococcus") infection, which is a major cause of morbidity and mortality in the US, causing community-acquired infections such as pneumonia, otitis media and meningitis. We show that the risk of infection is higher in elderly individuals and also in individuals of certain ethnic groups, although in a few reports obesity has been associated with better survival of individuals admitted to hospital with pneumococcus infection, a phenomenon known as "obesity paradox." We discuss factors that are associated with increased risk of pneumococcal infection, such as recent infection with RTI, chronic medical conditions, and immunosuppressive medications.

Keywords: aging; inflammation; obesity; pneumococcus; respiratory tract infections.

Figure 1

Obesity effects on different body systems involved in the response to respiratory tract infections. Obesity-induced changes in the lung may be due to higher weight load on the thorax and lead to reduced lung function. Obesity-induced changes in the immune system lead to chronic inflammation, immune activation, and reduced clearance of pathogens. Obesity also causes gastroesophageal reflux, which is a risk factor for aspiration pneumonia and asthma, due to the excess of belly fat posing pressure on the stomach, and gut microbiome dysbiosis. Cardiovascular complications of obesity include hypertension, dyslipidemia, and endothelial dysfunction. Obesity-induced changes in the adipose tissue are responsible for increased insulin resistance and glucose intolerance, both leading to chronic inflammation.