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Researchers Explore the Possible Link between CMV Infection, Obesity, and Metabolic Syndrome

Cytomegalovirus (“CMV”), a common virus that infects over half of adults by age 40, may cause changes in normal-weight women that could increase the risk of metabolic syndrome says new research led by investigators at the University of California, San Francisco (“UCSF”).

Most CMV infections are “silent,” meaning most people who are infected with CMV exhibit no signs or symptoms. However, CMV infection can be serious in certain patient populations, including newborns, when a mother is infected during pregnancy, and the immunocompromised. In addition, CMV is implicated in a number of chronic conditions where it is thought to act as a proinflammatory agent.

Metabolic syndrome is defined by the presence of multiple risk factors for type 2 diabetes and heart disease, including abdominal obesity, high blood pressure, and high blood lipid levels. Research in the obesity field has shown that low-grade inflammation, rather than obesity itself, contributes to the development of metabolic syndrome. This has led investigators to explore potential sources of low-grade inflammation to identify risk factors for metabolic syndrome, including CMV infection, which can elicit a sustained immune response in hosts even when no symptoms are present.

Study Design

UCSF researchers hypothesized that CMV could cause metabolic syndrome in some persons due to the sustained, low-grade inflammation caused by latent infection. To test this hypothesis, investigators examined the medical records of 2,532 adults between 20 and 49 years of age.

Study participants were screened for CMV infection status and were classified as having metabolic syndrome if they exhibited at least three of the following five risk factors:

  • Increased waist circumference
  • High blood pressure
  • Elevated triglycerides
  • Low HDL-C
  • Elevated fasting glucose

Study participants were also placed into one of four groups according to their body mass index (“BMI”):

  • Normal-weight (18.5 – 25)
  • Overweight (25 – 30)
  • Obese (30 – 40)
  • Extremely obese (>40)
Body Mass Index (“BMI”)

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Study Results

CMV was associated with metabolic syndrome in females but not in males (a result the UCSF researchers found “intriguing but not unfounded” because immune responses differ between men and women). Among all females, CMV infection was associated with a higher chance of developing metabolic syndrome. Interestingly, the association between metabolic syndrome and CMV infection varied with BMI.

After adjusting for multiple factors including age, race, and statin use, nearly 5% of normal-weight women infected with CMV had at least three risk factors for metabolic syndrome, compared to less than 1% of normal-weight women who were not infected. Surprisingly, in extremely obese patients the association was reversed – approximately 56% of CMV-infected women were classified as having metabolic syndrome compared to approximately 82% of women without evidence of CMV infection.

VBI believes this study may be important because it shows that even asymptomatic infection with CMV may be associated with potentially serious consequences, including an increase in risk factors for heart disease and type 2 diabetes in women of normal weight. The strong association between CMV infection and metabolic syndrome in normal-weight women suggests that CMV may cause long-acting, low-grade inflammation.

The decreased risk of metabolic syndrome in extremely obese patients with CMV infection is a surprising result. The researchers hypothesized that the replication of CMV might be accelerated in extremely obese patients, which would require a significant amount of lipids and potentially reduce the levels of fat circulating in the bloodstream. It is important to note that the prevalence of metabolic syndrome is significantly higher in obese patients than in normal-weight patients, regardless of CMV infection status.

More research is needed to understand these associations, the researchers said. It is important to note that the study did not prove a cause-and-effect link.