Epidemiologists found elevated levels of mercury and arsenic in 73 people who said they were following a gluten-free diet. All were participants in the National Health and Nutrition Examination Survey, which was performed between 2009–2014.
Both toxic metals are found in rice, and rice flour is a common substitute for wheat flour in gluten-free foods. According to Beth Mole, writing for Ars Technica: “Rice is known to be an efficient accumulator of arsenic and mercury, pulling the naturally occurring toxic substances up from soil and storing them. Researchers have estimated that rice plants are at least ten times better at sucking up arsenic than other grain plants.”
Since this is the first study to report such a finding, the authors aren’t sure whether such exposure will lead to significant health problems, but there is cause for concern. Long-term exposure to arsenic, mercury, and cadmium can increase the risk of cancer, heart disease, diabetes, respiratory problems, and kidney and brain damage.