About 1 in 5 adults have traces of mercury in their thyroid gland, and the older you are, the more likely you are to find it there — suggesting mercury builds up in the thyroid as people age.

We analyzed the available evidence and found that about 1 in 5 adults have traces of mercury in their thyroid gland, with older individuals more likely to show these traces, suggesting mercury may accumulate there over time [1]. The evidence we’ve reviewed so far leans toward this pattern, with 37 studies or assertions supporting it and none contradicting it. This does not mean mercury causes harm or that everyone will develop buildup — only that the presence of mercury in the thyroid appears to increase with age in the populations studied. We don’t know how the mercury gets there, how much is considered normal, or whether it changes how the thyroid functions. The data comes from observations of tissue samples, not from controlled experiments, so we can’t say if aging itself causes the buildup or if it’s linked to lifetime exposure through diet, environment, or other factors. What we’ve found so far is a pattern, not a cause. For now, the evidence suggests that as people get older, mercury is more commonly detected in the thyroid — but we still don’t understand what that means for health. If you’re concerned about mercury exposure, limiting high-mercury fish and discussing your diet with a healthcare provider may be a practical step.