he publication of Andrew Wakefield’s notorious and now discredited research on autism and vaccines in 1998 triggered a surge of worry about vaccine safety. Since then, questions about a purported connection between autism and vaccines have been asked and definitively answered: There is no link. But there are other factors linked to the development of autism that have solid scientific support.
A mountain of research has been conducted and published on a possible link between vaccines and autism, with hundreds of advocacy and scientific organizations refuting it. They also point out the public health risk of avoiding vaccinations. Yet the fear this unsubstantiated link has generated has led to the re-emergence of vaccine-preventable diseases such as measles and pertussis. Another consequence of the ongoing media attention paid to the issue is a misunderstanding of the real environmental risk factors associated with autism.
During the last year or so, there has been a steady drumbeat of media coverage about autism and vaccines. Politicians, celebrities, the presidential election, film festivals, and mythical conspiracies all contributed to mainstream news and media story lines on the false link between vaccines and autism. Many of them had nothing to do with real science, nor were they the result of research findings that helped families.
But during the same period, a dozen new scientific findings were published on legitimate environmental factors, including toxic chemicals, maternal infection during pregnancy, and chronic stress. These rarely made headlines, with the media spotlight remaining on the myth. Yet knowledge and understanding of these real environmental factors could lead to actual therapies or ways to prevent the debilitating symptoms of autism.
The term “environmental factor” is often misunderstood and used incorrectly. Scientists consider anything that produces a biological or behavioral response that isn’t strictly due to genes to be environmental. This includes what we eat and drink, what we breathe, what touches our skin, and the like. Also worth clarifying is the difference between a “risk” and a “cause.” A cause is something that makes a disease happen. Risk factors, by comparison, are things that act in concert to nudge us toward disease.
Specific criteria have been laid out to determine if something is a cause or a risk factor. So far, no single environmental factor has met the criteria for being a cause of autism. This indicates that environmental factors work together, or interact with genes, to lead to autism.
Here are a few examples of environmental factors that that have been linked to autism:
- Exposure to the anti-epileptic drug valproic acid during pregnancy
- Older age of the mother or father
- High levels of air pollution during pregnancy. This association has been subjected to a systematic review and withstood scientific rigor. Genes control this association.
- Extreme illness or infection during pregnancy, including severe reactions to bacterial and viral infections (some of which can be prevented through vaccination)
- Obesity during pregnancy, premature birth, and complications during birth, likely as the result of interactions with genes
Exposure to these factors elevates a child’s risk of developing autism anywhere between two and four times. An exhaustive review of these factors was just published in the Annual Review of Public Health.
A prime example of the distraction associated with the vaccine/autism myth is the role of mercury. Mercury is released into the environment, primarily by burning coal and other things that have mercury in them. Every hour, 11 pounds of mercury are released into the environment this way. As this mercury is distributed into the environment, bacteria convert it into methylmercury. This type of mercury can accumulate in food sources, such as fish, and also in our bodies. A high level of methylmercury in the body can affect brain development in children.
Another form of mercury, ethylmercury, isn’t found in the environment. Instead, it is created in labs and was used in making thimerosal, a preservative in vaccines. While research has exonerated thimerosal as a risk factor for autism, it has been removed from most vaccines given to children under 6. Ethylmercury does not accumulate in the body and does not pose the same public health threat as methylmercury.
Scientists agree that methylmercury and ethylmercury have different toxicological and biological profiles, and should not be used interchangeably.
Mercury emissions from burning coal and medical waste can be reduced, which would minimize the potential harm to our children. The already strained EPA has had success doing that, but in order to continue reducing mercury in the environment, its activities need to be supported, not diminished. Mercury in the environment is not an issue one government agency, or one country, can address alone.
The media — and thus the public — have been distracted from the real threat to children and public health posed by methylmercury by groundless claims about ethylmercury in thimerosal by Robert F. Kennedy Jr. and others. Plenty of outrage has sadly been misdirected.
If Kennedy, who has claimed he is going to lead a presidential panel on vaccine safety, is truly interested in helping families with autism and making all children safer, then the $100,000 reward he and actor Robert De Niro offered during a recent publicity stunt to find an autism-thimerosal link would be better spent funding scientists doing research on the real causes of autism and how best to care for individuals diagnosed with the disease. Alternatively, that money could be spent toward reducing the existing public health threat of methylmercury.
Researchers and advocacy organizations have moved on from the vaccine-autism story line to focus on issues that truly affect families, such as understanding the real causes of autism, finding ways to diagnose it earlier, developing more effective treatments, and offering better access to those treatments. With every minute wasted talking about the autism-vaccine myth and every dollar spent on researching this dead end, we are losing ground and failing families who deserve real answers on the causes of autism and more help for their loved ones.
Alycia Halladay, PhD, is the chief science officer at the Autism Science Foundation and an assistant adjunct professor in the Department of Pharmacology and Toxicology at Rutgers University.