Feb 16, 2017
The Unintended Consequences of a Gluten-Free Diet.
A study found that people who reported to be on gluten-free diets had levels of total arsenic in their urine which averaged about 50% to 90% more than found in people not eating gluten-free diets (Bulka, Epidemiology 2017).
The study also found 70% more mercury in the blood of gluten-free eaters, although when focusing on just the inorganic (i.e., more toxic) form, the level was just 10% higher than the non-gluten free eaters.
However, careful review of this study shows that the amounts of arsenic in both the gluten-free and regular eaters were actually very low (respectively, 12 mcg/L and 7.8 mcg/L) for total arsenic -- much lower than the 50+ mcg/L levels of total arsenic associated with arsenic toxicity (Oregon Poison Center 2012). Similarly, the levels of mercury in the blood were very low. Levels above 5 mcg/L are reportable to state health agencies and levels above 100 mcg/L are associated with clear signs of mercury poisoning (New York State Dept of Health, 2016), but the levels found for gluten-free eaters and regular eaters, respectively, were just 1.3 mcg/L and 0.80 mcg/L. Furthermore, when focusing only on the more dangerous form of mercury, inorganic mercury, the levels were nearly identical: 0.30 mcg/L and 0.28 mcg/L, respectively.
The researchers speculated that rice may be contributing to the higher concentrations of arsenic in gluten-free eaters because it is the primary substitute grain in gluten-free products. It is true that certain rice products are known to contain higher amounts of arsenic, particularly brown rice. However, the researchers did not mention that the most common reason for arsenic and mercury levels to be elevated is fish consumption and this was not accounted for in the analysis. In fact, a fish meal can elevate total arsenic levels by more than 200 mcg/L (although this is from organic arsenic -- the safer form) and levels return to normal within two to three days (Kales, J Analyt Tox 2006).
If gluten-free eaters eat more fish than other people (which seems likely, as gluten-free eaters are health conscious in their food selection) this would explain higher arsenic and mercury levels in their bodies.
The bottom line:
While it's best to minimize exposure to arsenic and other heavy metals, the higher amounts of arsenic and mercury found in the urine and blood of gluten-free eaters do not appear to represent a health concern, and it is not at all certain that they were due to gluten-free foods.
(If you are on a gluten-free diet, be aware that oats are naturally gluten-free, but that some oat cereals contain significant amounts of gluten due to cross-contamination during processing.