Individuals who adopt a gluten-free diet are putting themselves at risk for uncommonly high levels of arsenic and mercury, according to the findings of a recent study published in Epidemiology.

“Despite [less than] 1% of Americans having diagnosed celiac disease, an estimated 25% of American consumers reported consuming gluten-free food in 2015, a 67% increase from 2013,” wrote the authors of the study, led by Maria Argos, PhD, of the University of Illinois at Chicago. “Despite such a dramatic shift in the diet of many Americans, little is known about how gluten-free diets might affect exposure to toxic metals found in certain foods,” they noted.

Dr. Argos and her colleagues analyzed data collected from the National Health and Nutrition Examination Survey (NHANES), which included self-reported questionnaires in which subjects indicated what type of diet they were on, if any. Data on those who indicated that they followed a gluten-free diet were analyzed to determine if their urinary and blood biomarkers indicated any exposure to toxic metals. A total of 7,471 subjects from the NHANES were included in the analysis .

“We accounted for the complex sampling design of NHANES [by] using Taylor series linearization and sampling weights, per the NHANES analytic guidelines, to ensure unbiased and nationally representative estimates,” the authors explained.

A total of 73 subjects identified themselves as following a gluten-free diet. Within this group, the mean total arsenic level in urine was found to be 12.1 mcg/L, compared to 7.8 mcg/L for the other 7,398 subjects. Levels of dimethylarsinic acid averaged 5.3 mcg/L for those who were gluten-free, but only 3.7 for everyone else, while cadmium and lead levels were also slightly higher for gluten-free individuals: 0.18 mcg/L vs. 0.16 mcg/L, and 0.40 mcg/L vs. 0.37 mcg/L, respectively.

Blood analyses showed that total mercury levels were also substantially higher in the gluten-free group, at a mean of 1.3 mcg/L compared to 0.8 mcg/L. While cadmium levels were the same between the two – both showed a mean level of 0.29 mcg/L – lead measured 1.1 mcg/dL and inorganic mercury measured 0.30 mcg/L, compared to 0.96 mcg/L and 0.28 mcg/L in everyone else, respectively.

Geometric mean ratios showed that total arsenic, total arsenic 1, and total mercury levels had the largest disparity between the two groups. Total arsenic registered a 1.5 (95% CI, 1.2-2.0), total mercury a 1.7 (95% CI, 1.1-2.4), and total arsenic 1 a 1.9 (95% CI 1.3-2.6), meaning the gluten-free group had nearly double the risk for higher levels than those on other diets.

“These findings may have important health implications since the health effects of low-level arsenic and mercury exposure from food sources are uncertain but may increase the risk for cancer and other chronic diseases,” Dr. Argos and her coauthors concluded, adding that “future studies are needed to more fully examine exposure to toxic metals from consuming gluten-free foods.”

The study was funded by a grant from the National Institutes of Health. Dr. Argos and her coauthors did not report any relevant financial disclosures.


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