Recently, there has been an eruption of stories in the media about vaccination, and no wonder. Between this season’s flu strain and the once previously eradicated measles, this has been a bad winter for vaccine-preventable infectious diseases. A number of factors contribute to vaccine effectiveness—most obviously, the rate at which people get vaccinated. However, it may surprise you to know that obesity can also play a role.
Nutrition, viruses, and obesity
Currently, more than a third of adults in the United States are obese (as defined by their body mass index). Obesity is the leading preventable cause of illness and a major contributor to increasing chronic disease rates. Another public health threat is the flu, which can kill anywhere from 3,000 to 49,000 Americans each year.
So, where do these two intersect?
During the 1990s, studies in Cuba revealed that during times of high nutritional stress, viruses mutated more rapidly. However, when vitamins were given to the population viruses returned to normal rates. It became apparent that adequate nutrition was an essential factor in reducing viral infections. In addition to protecting against viral infections, a healthy diet can protect against chronic-related diseases, including obesity, type II diabetes, heart disease, and some cancers.
Obesity and the flu vaccine
Fast forward to 2005: researchers at my alma mater, the Gillings School of Global Public Health at University of North Carolina (UNC), found that obese mice infected with the flu had a 60 percent mortality rate compared to only 4 percent of lean mice. During 2009 flu season, researchers recognized that obesity was associated with a weakened immune response to the flu vaccine. This prompted a research team from UNC to study the relationship between obesity and its effect on the immune system. One the study’s leading researchers, Dr. Melinda Beck, hypothesized that antibody response to the flu vaccine would be poorer in individuals with obesity when compared to healthy weight individuals.
Between 2009 and 2010, Beck’s study enrolled approximately 1,000 flu vaccine participants aged 18 to 80 at a primary care clinic. Study staff measured participant’s antibody levels one month after getting vaccinated and then again at 12 months. Results revealed that within one month of getting vaccinated, all study participants developed the antibodies to the flu. However, antibodies in obese participants declined much more quickly than antibodies in healthy weight participants. By 12 months, antibody levels in 50 percent of obese participants had a four-fold decrease, compared to only 25 percent of healthy weight participants.
In other words, obesity appears to reduce the effectiveness of the flu vaccine in individuals. And because of the phenomenon of “herd immunity,” the consequences impact us all—regardless of weight status.
The power of prevention
The growing rate of obese individuals in the United States makes it very important to determine how and why extra weight affects the body’s response to fight infection. But this research also provides another reason for public policies to help individuals engage in healthy behaviors and prevent obesity.
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