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Why Does Autism Impact Boys More Often Than Girls?

Exposures to inorganic mercury in the processed food supply might be a reason

This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American


According to the CDC, autism prevalence continues to climb with 8 year old boys afflicted 4.5 times more often than girls. What makes matters worse is the fact that many boys with autism are also diagnosed with ADHD. These disorders severely impact the learning process in the classroom environment and lead to a lifelong economic burden both for the afflicted individual and society. Researchers estimated the annual economic burden in the U.S. for autism alone in 2015 was $162-$367 billion. If the autism prevalence continues to rise, researchers predict the costs will likely exceed those of ADHD and diabetes by 2025.

It is imperative that families receive the support they need to prevent and manage these disorders which often occur in tandem. Proper management requires an understanding of the causes or “risk factors.” One cause associated with both disorders is exposure to heavy metals found in a poor diet. Heavy metal exposures may occur from the consumption of highly processed foods that contain ingredients with allowable concentrations of lead and inorganic mercury. Furthermore, these heavy metals may accumulate in blood especially when diet does not include adequate minerals to support the gene activity needed to metabolize and excrete them. Researchers led by Alabdali recently found higher blood lead and mercury levels are correlated with the severity of social and cognitive impairment in children with autism. What this means is parents will have more difficulty managing their child with autism and ADHD as the mercury and/or lead concentration levels rise in his blood.

How do we know for sure there is a link between dietary exposure to these two particular heavy metals and autism and/or ADHD? Long ago, Kate Mahaffey, led a research team to study the dietary factors in American children that lead to the accumulation of lead in their blood. The researchers studied the blood results of 3,000 American children that were analyzed as part of the National Health and Nutrition Examination II Survey (NHANES). They found a significant and independent inverse relationship between dietary calcium intake and blood lead concentrations. What this means is children who consumed less calcium rich food had higher blood lead concentrations.  Most everyone knows higher blood lead concentration is a known risk factor for the development of ADHD and developmental delay in all children. But what about blood mercury and autism in boys?


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The mercury-in-vaccine “cause” of autism has been debunked by the public health community. The mercury compound thimerosal was removed from children’s vaccines about 15 years ago yet we still have increasing numbers of children being diagnosed with autism.  Mercury in food however may be linked to autism in boys.  Just this year, researchers led by Andres Cardenas at Harvard University found mercury in the red blood cells of cord blood impacts the PON1 gene expression in little boys but not girls through childhood. In other words, the mercury that mother consumed in her diet ended up in her baby boy and this mercury suppressed her baby’s PON1 gene before and after birth and all the way through mid-childhood. The researchers found the PON1 gene suppression in the cord blood predicted lower cognitive functioning in boys during their early childhood. This may be the proverbial smoking gun. PON1 gene expression is required to produce the enzyme we all need to break down organophosphate pesticide residues found in our food supply

Where there is smoke there is fire. It turns out mercury, inorganic mercury, not the kind of mercury you find in fish, has been rising for many years in American blood. This could explain the connection between mercury and PON1 gene suppression in little boys. A researcher by the name of Dan Laks analyzed the 1999-2006 NHANES data set for 6,174 women between the ages of 18-49 to determine trends in their inorganic mercury levels. He analyzed the blood results and found inorganic mercury detection rose sharply from 2 percent in 1999-2000 to 30 percent in 2005-2006. In other words, only 2 percent of women of childbearing age had detectable levels of inorganic mercury in their blood at the end of 2000 but by 2006 the number of women with detectable levels of inorganic mercury rose to 30 percent.  Dr. Laks concluded that inorganic mercury must be accumulating within the human body due to long term exposures. Where is all this inorganic mercury coming from?

For starters, the chlorine used to bleach flour may contain up to 1 ppm inorganic mercury according to international regulations which all countries must obey. The average American consumed 94 pounds per year of wheat flour in 2015 according to the USDA food availability data system. How much of that flour was bleached remains unknown but you can bet most Americans do not know that bleached flour may contain up to 1 ppm inorganic mercury. Nor do they know increasing inorganic mercury levels in their blood is associated with the development of type-2 diabetes. By reducing your consumption of white flour products, you may reduce your exposure to some of the inorganic mercury in the food supply but not all. In addition to bleached flour, inorganic mercury may be found in many other food ingredients.

According to a 2013 safety certification document on vegetable oil refining, it turns out there is a significant risk of inorganic mercury contamination in vegetable oils (aka “unhealthy fats”) due to the use of chemical processing aids. USDA reports the average American consumed 36 pounds of vegetable oil in 2010. And of course, mercury can still be found in food products containing fructose and high fructose corn syrup according to comments published in the Environmental Health Journal by Canadian researcher Karen Rideout in 2010.  USDA reports the average American consumed about 25 pounds of high fructose corn syrup in 2015. So there is more to “fat” and “sugar” than meets the eye. Then there are the food colors yellow #5 and yellow #6 which may also contain up to 1 ppm inorganic mercury and up to 10 ppm lead according to the U.S. Code of Federal Regulations. There are many other ingredients in the American food supply that may contain allowable mercury and/or lead.

The inconvenient truth is the American food supply is contaminated with inorganic mercury and this mercury may be impacting child development. As inorganic mercury levels continue to rise in the American population via unhealthy diet we are seeing an increase in the prevalence of autism. In addition to inorganic mercury, the allowable levels of lead in the food supply are likely facilitating the increasing prevalence in ADHD.