Obesity and Viruses

Since 1980, the prevalence of obesity among children and adults continues to increase worldwide. The implications for the health of obese or overweight individuals are tremendous. Some of the potential complications include hypertension, Type 2 diabetes, coronary heart disease, stroke, osteoarthritis, gallbladder disease, sleep apnea, and cancer (breast, uterine, colon). The economic burden caused by obesity and its complications is reaching alarming proportions. Therefore, it is important to evaluate all possible causes of such persistent obesity epidemic to offer effective treatments. Although viral causes of obesity remain a very controversial idea, the growing number of studies suggests a link between a common virus and obesity.

There are complex regulatory pathways in the human body that influence body weight. Certain hormones produced in the body can signal the brain to affect our appetite and energy expenditure. In addition, genes and environment are important causes of obesity. Heredity, including a number of inherited genetic disorders (such as Prader-Willi syndrome and Bardet-Biedl syndrome), and gene mutations may contribute to rising incidence of obese individuals. However, more popular view is that of the environmental factors being the most important causes of obesity. These [Page 549]factors include diet, portion size, physical activity, cultural, social, economical, and educational influences.

Infectious agents, such as viruses and bacteria, are increasingly linked to many common chronic diseases. Bacteria are microscopic organisms (organisms that can be seen only through a microscope) that are composed from one cell and can cause disease or perform an important role as part of the human body (help with digestion). Viruses are infectious particles; they are not made of cells, but contain a shell with their DNA (hereditary information) inside. Viruses can reproduce and function only when they invade other cells. The treatment for bacterial infections often includes antibiotics. Vaccines offer a good protection against viruses.

Because obesity is such an important risk factor for many chronic conditions, studies have originated to explore a possibility of an infectious agent being associated with obesity. In the past two decades, it has been observed that certain viruses are associated with increased incidence of obesity in animals. These viruses were different strains of a common virus found in humans, called adenovirus. This virus is often associated with the common cold, flu, meningitis (inflammation of the membranes covering the brain), and diarrhea in some cases. Interestingly, the link between this virus and obesity in animals was discovered around the same time as the prevalence of obesity began to increase (1980).

Specifically, a strain of virus, called adenovirus-36 (Ad-36), has been shown to cause obesity in chickens, mice, and nonhuman primates. Researchers found that Ad-36 may increase the number of fat cells, which makes the animal store more fat. Recently, it was also discovered that obese or overweight individuals have a higher prevalence (20 to 30 percent) of the virus than slim or normal-weight individuals (11 percent). Infection with Ad-36 presents with only mild cold-like symptoms that may last one or two days. The presence of the virus grants some positive outcomes. It has been observed that in animals with Ad-36 virus, the levels of low-density lipoprotein cholesterol (LDL-C) (the “bad cholesterol” that accumulates deposit in the arteries) were decreased.

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