Obese Are More Susceptible to Respiratory Infections

Persons who are obese are at increased risk for catching the flu and other potentially serious respiratory diseases, according to a new study that adds more evidence that obesity alters the body’s immune system, leaving heavy persons vulnerable to respiratory infections.

“Being sick-even if it is just a cold-is not fun, and reducing the frequency of respiratory infections is desirable for anyone. Most obese patients are already well aware of the risk of diabetes and other chronic conditions associated with obesity, but they probably aren’t aware of the immunosuppression and increased risk of acute infections as well,” Jeffrey Kwong, MD, from the Institute for Clinical Evaluative Sciences, Toronto, told ConsultantLive.

Earlier studies have shown that antibodies produced in response to flu shots plunge dramatically among obese persons compared with those who have healthy weights. Dr Kwong and colleagues, including lead author Michael Campitelli, MPH, conducted a retrospective cohort study for a period of 13 years involving more than 100,000 persons in Ontario, Canada, who responded to population health surveys. The researchers observed higher rates of outpatient visits to a physician’s office or emergency department for acute respiratory infections during the influenza season for those who were overweight and obese compared with normal weight persons-even though the heavier persons were more likely to be vaccinated.

The increased risk was highest among those who were the heaviest; the rates were 20% higher in severely obese persons who had a body mass index (BMI) of 35 kg/m² or higher than in persons of normal weight. The researchers also saw lower but similar increased risks of respiratory infections among the obese persons during seasons when flu was not circulating.

“Obese people with a BMI of 30 or higher had more outpatient visits for acute respiratory infections during both influenza and non-influenza seasons,” said Dr Kwong. “This suggests that obesity not only increased the risk for influenza infection, but for other respiratory pathogens, likely both viral and bacterial.”

Deficits in the immune system can impair the response to respiratory pathogens and enhance susceptibility to infections. “Both animal and human studies have noted immune function deficiencies among those who are obese,” Dr Kwong said. “There is decreased thymic output of naive T-cells, lowered T-cell and B-cell proliferation in response to antigen/mitogen stimulation, and reduced circulating natural killer cells with diminished activity.”

In fact, losing weight may help boost the immune system for obese persons. “Studies of cell function in obese people have shown improvements in immune responsiveness following weight loss or dietary restriction,” Dr Kwong said. “For example, obese individuals showed increased T-cell responsiveness to mitogen following a weight reduction program. Therefore, reducing weight in an obese person may help improve some of the obesity-related immune deficiencies, leading to a more robust response against respiratory pathogens.”

The bottom line is that “this represents yet another potential motivator for obese people to lose weight,” said Dr Kwong. “We hope this study will help clinicians raise awareness about this.”

The researchers published their results in the January 2014 issue of the International Journal of Obesity.