A Comparison of Mercury Exposure from Seafood Consumption and Dental Amalgam Fillings in People with and without Amyotrophic Lateral Sclerosis (ALS): An International Online Case-Control Study

Abstract

Exposures to toxic metals such as mercury have been suggested to be risk factors for amyotrophic lateral sclerosis (ALS). Human intake of mercury commonly occurs via consumption of seafood or from mercury-containing amalgam dental restorations (‘mercury fillings’). We therefore compared mercury exposures from these sources in 401 ALS and 452 non-ALS respondents, using an internationally-available online questionnaire that asked respondents how often they ate seafood and what their favourite types of seafoods were. Respondents were also asked to record numbers of current or former mercury fillings. ALS and non-ALS respondents did not differ in their frequency of seafood consumption or in monthly mercury intake from favourite seafoods. Both groups had similar numbers of current, as well as former, mercury fillings. In conclusion, this study found no evidence that mercury exposure from eating seafood, or from mercury dental fillings, was associated with the risk of developing ALS. Therefore, if mercury does play a role in the pathogenesis of ALS, other sources of exposure to mercury in the environment or workplace need to be considered. Alternatively, a susceptibility to mercury toxicity in ALS, such as genetic or epigenetic variations, multiple toxic metal interactions, or selenium deficiency, may be present.

The distribution of toxic metals in the human retina and optic nerve head: Implications for age-related macular degeneration

“…Cell turnover in the RPE is slow or absent in the normal adult retina [ 42 ], so continuous or repeated exposures to toxic metals are likely to result in accumulation of these xenobiotics over time. Another possible reason for the late appearance of AMD is that most of our eye samples appeared to contain organic mercury; human exposure to organic mercury from consuming mercury-containing seafood is common [ 43 , 44 ], and it takes years for organic mercury to be converted in cells to toxic inorganic mercury [ 45 ].…”

“…Total mercury detected on LA-ICP-MS was widespread in the posterior segment of most eyes, but inorganic mercury was seen in the RPE in only one eye. This suggests most of our donors were exposed to organic mercury, probably from seafood consumption since over 90% of Australians report eating seafood regularly [ 44 ]. This implies that organic mercury can be cleared from cells in the posterior segment of the eye apart from those in the RPE, where mercury is bound to melanosomes [ 3 ].…”

Elemental imaging shows mercury in cells of the human lateral and medial geniculate nuclei

“…Lysosomes play an important part in many cell processes [37], some of which could be affected by large amounts of mercury. A potential clinical correlation of this pattern of mercury deposition comes from individual G2, a fisherman who drowned at sea, who probably had a diet rich in fish, with large predatory fish having a high mercury content [38]. 2The pattern of fine particulate neuronal mercury, as well as diffuse mercury in the neuropil (Fig 3C), is likely to result from recent exposure to mercury.…”

“…(2) We do not know how and when our study population were exposed to mercury. In a future study, people who have frequent hallucinations could be asked to keep a detailed diary of dietary intake (especially of mercury-containing fish), bruxism or dental manipulations what might increase mercury uptake from silver amalgam dental restorations, and occupational activities that could expose them to mercury [38], to see if any mercury-related associations with the onset of hallucinations could be found. This could be expanded to population studies to see if the frequency of hallucinations increases in people exposed to mercury from small-scale gold mining [61], living near coal-fired power stations [61], volcanic activity [62], or wildfires [63][64][65].…”

Keratinous biomarker of mercury exposure associated with amyotrophic lateral sclerosis risk in a nationwide U.S. study

“…Methylmercury exposure via fish consumption has been suggested as an ALS risk factor; however, evidence from questionnaire-based studies is mixed (9)(10)(11). The relationship between ALS and fish consumption is complex due to beneficial components, such as omega-3 polyunsaturated fatty acids (12).…”