Is Obesity Contagious?
The worldwide prevalence of obesity has increased dramatically in the last several decades. Obesity is a significant public health problem in most developed countries and carries with it substantial morbidity and mortality. The most commonly implicated causes of obesity are well known: poor diet, lack of physical activity, and genetic predisposition. There are also other factors that contribute to obesity, including environment, cultural customs, seasonal changes, stress, and medication-related weight gain. However, a new theory provides another possible cause for obesity in some people: infectious disease.
The term “infectobesity” was coined several years ago by researchers who discovered a link between a common human viral pathogen and obesity. Adenovirus-36 (Ad-36) is a highly contagious virus that normally causes upper respiratory tract infections. There are approximately 50 members of the adenovirus family, and they cause up to 5% of respiratory tract infections each year, ranging from the common cold to severe pneumonia. Some strains can also cause eye infections. Ad-36 has not been linked to any specific disease to date.
Early research found that 30% of obese people were infected with Ad-36, while only 11% of non-obese people were infected. New research finds that Ad-36 has a direct effect on human fat stem cells. The virus infects the fatty tissue and increases replication, differentiation, and accumulation of fat cells. Ultimately, this leads to larger fat cells, and more of them. The virus also increases lipid sensitivity and decreases leptin secretion of the new fat cells. However, the weight gain was not permanent in every case, lasting only long enough for the infected person to build up resistance to the virus.
Several other viruses have shown similar effects in animals: canine distemper virus, Rous-associated virus type 7, Borna disease virus, scrapie agents, and SMAM-1, an avian adenovirus from India. Also, 2 other human adenoviruses (Ad-5 and Ad-37) have induced weight gain in animal models, but have not had the same effect in humans. Most of the studies have taken place in animal models, and human data is limited, but some studies of rodents and non-human primates can be extrapolated to human models.
The increase in obesity cannot be entirely explained by changes in diet, physical activity, television watching, and food advertisement. The rapid spread of obesity is analogous to the spread of an infectious disease, and the viral etiology of obesity is appealing as an explanation to the public health crisis. If we better understand the origin of fat cell differentiation, growth, and accumulation, we can better treat obesity and its constellation of complications.
This virus is clearly not the only explanation for obesity, and researchers and clinicians only offer the theory as one possible contributing factor. It is still important to eat healthy, exercise often, and manage stress to stay healthy and decrease the spread of all infectious diseases, whether or not they cause obesity.
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