Michelle Obama has dedicated her issue advocacy as America’s First Lady toward solving the childhood obesity problem. Even the World Health Organization has pronounced childhood obesity one of the most serious public health challenges of the 21^st century. Concerns about heart disease, type 2 diabetes, asthma, sleep apnea and social discrimination are among some of the most serious consequences of the obesity epidemic, making it worthy of Obama’s high profile “Let’s Move” initiative.

What if this health crisis is linked to another government health policy that has the firm backing of the pharmaceutical and health care industries, government agencies, legislatures, the military, and education systems?

New research linking childhood obesity to a vaccine ingredient, thimerosal, provides evidence that obesity may also have an acquired biological risk factor  that is independent of lifestyle risk factors such as eating high fat, high sugar processed foods, a lack of exercise and too much screen time. This risk factor is primarily acquired in childhood, matching the age group that is most affected and it is even targeted toward pregnant women and their developing fetuses.

Obesity is now being diagnosed in the youngest of age groups. A whopping 43 million children worldwide under age 5 were overweight or obese as of 2010, a 60% increase compared with preschoolers in 1990. What is the impact of obesity, and how have exposures and lifestyles contributed to the childhood obesity epidemic?

 In the United States, childhood and adult obesity have become so far-reaching and costly—with severe obesity costing the nation $69 billion in 2013 alone—that “fat” is being characterized as “the new normal.” The just-released update from the U.S. Centers for Disease Control and Prevention (CDC) optimistically reports a leveling off of childhood obesity, but given that one-fifth (18%-21%) of 6-to-19-year-olds remains obese (versus 5%-7% of comparably aged children in 1980), there is still little cause for celebration.

 While childhood obesity sits squarely on the mainstream public health agenda, concerns about childhood exposure to mercury has been shut down. As recently discussed on this website, conflicts of interest have prevented the adverse health outcomes resulting from mercury exposure from achieving the broad attention and response that they deserve. Now, a public health study in the Journal of Preventive Medicine & Public Health by David Geier and coauthors—“Thimerosal-containing hepatitis B vaccine exposure is highly associated with childhood obesity: a case-control study using the Vaccine Safety Datalink”—provides convincing evidence that Thimerosal (a man-made ethylmercury preservative) is an environmental obesogen (i.e., trigger) contributing to the spike in childhood obesity in recent decades.

 What does mercury have to do with obesity?

 The U.S. Environmental Protection Agency states that mercury in all its forms is “quite toxic” and capable of producing a dizzying array of harmful human health effects. Among these, mercury functions as a potent endocrine disrupter—a chemical that alters hormonal functions. According to the National Institute of Environmental Health Sciences, endocrine disruptors pose especially severe risks during prenatal and early postnatal development.

 To investigate early postnatal risk, Geier and colleagues considered infants’ repeat exposure to Thimerosal-containing hepatitis B vaccines, which began to be recommended and administered in the early 1990s. Specifically, the study evaluated the relationship between Thimerosal exposure during the first six months of life and subsequent risks of a childhood obesity diagnosis—a relationship never before addressed in the scientific literature. The authors used medical records from the Vaccine Safety Datalink (VSD) database, a collaborative project between the CDC and health care organizations across the U.S. The database provides access to routinely collected information on vaccines as well as medical illnesses diagnosed at doctors’ offices and during urgent care, emergency department, and hospital visits. Unfortunately, VSD data are not available for examination beyond the year 2000, and the database does not allow more than one vaccine to be considered at a time, making it impossible to include multiple Thimerosal-containing vaccines in a single study.

 Study design

 To test their hypothesis, Geier and coauthors designed a case-control study, looking at children (approximately evenly split between males and females) who were continuously enrolled in three health maintenance organizations participating in the VSD project. Case-control studies allow researchers to compare people who have a specific condition or disease (in this instance, children diagnosed with obesity) with people who are similar but do not have the condition or disease (children not diagnosed with obesity). The following table outlines key elements of the study design:

¹VSD data not available for study beyond the year 2000.

²Counting the first instance of diagnosis using established diagnostic codes for obesity/overweight.

³Age selected to reduce the chance of choosing controls who would subsequently receive an obesity diagnosis.

Strong evidence of a relationship

 The study’s methodologically robust findings indicate that exposure to organic mercury via Thimerosal-containing hepatitis B vaccines administered at intervals in the first six months of life “significantly increased the long-term risk of a child being diagnosed with obesity.” Using odds ratios, which represent the odds that an outcome will occur given a particular exposure, the study found:

•  A significantly greater risk of an obesity diagnosis for children who received any Thimerosal-containing hepatitis B vaccine within the first six months of life (versus children who either received no hepatitis B vaccine or received a Thimerosal-free hepatitis B vaccine)

1. A significantly higher risk for children who received three doses of hepatitis B vaccine (versus fewer or none) within the first six months of life, indicating a dose-response relationship.

 The study’s authors also elegantly outline several additional factors that support their findings:

 Matching time trends—children’s exposure to Thimerosal-containing vaccines increased (and decreased) at the same time that the prevalence of diagnosed childhood obesity increased (and began declining).

• Biological plausibility—including the fact that fat cells (adipocytes) develop primarily during late fetal and early postnatal life and are especially vulnerable to environmental stressors during this time.

• Study methods that allowed the researchers to consider variations in the timing of vaccine administration and in levels of exposure to Thimerosal.

 Children still exposed to Thimerosal

 Public health problems receive attention when various “triggers for strong public action” begin to coalesce. In the case of childhood obesity, evidence-based research, changing social norms, and self-help movements for overweight/obese individuals have succeeded in marshalling a concerted public health response. Geier and coauthors point out that children and pregnant women continue to be regularly and abundantly exposed to mercury through routine administration of Thimerosal-containing influenza vaccines. Unfortunately, it would appear that more powerful catalysts for action—including advocacy, coordinated campaigns, and targeting of industries contributing to the problem—will be needed before regulators and manufacturers heed the evidence and remove Thimerosal from all vaccines.