The accumulation of heavy metals in a child's blood has been linked to social and cognitive deficits in children diagnosed with autism.
More specifically, it appears that high levels of inorganic mercury (not the mercury found in fish), in a pregnant woman's diet may suppress PON1 gene expression in boys (not girls). This gene is essential for "breaking down" pesticide residues, including inorganic mercury, that enter the body.
Related: Reduce the Amount of Lead your Child is Exposed To: Here's How
Most of us are likely aware that it is a bad idea to be in contact with the mercury found in thermometers. We also know the importance of monitoring our dietary intake of high-mercury fish. Yet, how often are we encouraged to reduce our dietary intake of inorganic mercury?
Where in our kitchens might inorganic mercury even be found?
The prime suspect is chlorine-bleached flour, which may contain 1 ppm (part-per-million) inorganic mercury. Other sources include vegetable oils contaminated with inorganic mercury, foods that list fructose and high fructose corn syrup (HFCS) on the ingredient list, and additives used to artificially color food (ex. yellow #5).
Researchers have detected a wide range of mercury levels in a variety of foods containing HFCS, from not perceptible to 0.570 micrograms per gram of high fructose corn syrup. While this does not sound like a lot, in 2009, it was estimated that the average intake of HFCS was around 50 grams per day. In case you were wondering, like me, why mercury is in HFCS anyway, it appears that mercury grade caustic soda (sodium hydroxide) is used in the manufacturing process.
The research did not specify whether inorganic mercury or metallic mercury was evaluated specifically, although the authors of the study point out, either way, it is an "extremely potent neurological toxin."
In a counterpoint to the argument that inorganic mercury levels are connected to a rise in autism, some believe that they are not linked, and in fact, levels of inorganic mercury in the blood are decreasing despite increased autism diagnosis. It was also argued that the ratio of boys to girls with autism is skewed and that we are better at diagnosing symptoms of autism in boys.
So, what should we believe? Should we be concerned about inorganic mercury in our food?
I believe we should, but not always due to the mercury specifically (unless we are talking about high-mercury fish).
We should ALL be concerned about our dietary intake of processed foods. Many of the foods mercury has been detected in are highly processed and are foods that are best avoided anyway for myriad reasons. Like Michael Pollen says, we probably should not be eating anything that our grandparents (perhaps great-grandparents) do not recognize as food.
Overall, increased risk of autism or not, I do also believe we should also be concerned about contact with mercury from a variety of sources including amalgram dental fillings and environmental exposures.
Even low-dose exposures in pregnancy are linked to neurological effects in baby and elevated levels in umbilical cord blood have still been associated with lower infant IQ and other neurodevelopmental effects.