I am writing to alert physicians to a common but infrequently considered source of mercury.
I recently saw a young woman who was referred to me because of high levels of blood mercury. The patient, who was 26 years old, had been diagnosed with multiple sclerosis (by MRI) following a bout of optic neuritis and peripheral neuropathy, both of which resolved spontaneously. Yet because of her interest in a possible correlation between mercury levels and dental fillings, she had asked her family physician to measure her blood mercury level. The result, 63 nmol/L, was markedly elevated (normal 0 to 49 nmol/L). However, several case–control studies have failed to find a relationship between dental amalgams and development of multiple sclerosis.1,2,3
On examination she appeared well and physical examination was entirely within normal limits.
Past medical history revealed a childhood exposure to mercury brought home by her father, who was a dentist, and more recently to a broken mercury-containing thermostat in her apartment. (Mercury poisoning has resulted from exposure to devices that contain mercury such as sphygmomanometers.4)
The patient lived with her mother and both women worked at a local hotel. There had been recent renovations to interior of their apartment including replacement of drywall. The building was 35 years old. She had no unusual hobbies that might have exposed her to mercury. Both she and her mother consumed health food supplements. Her mother's levels of blood mercury were normal.
Further questioning revealed that both the patient and her boyfriend enjoyed sushi and other seafood, eating out at restaurants 4 to 5 times a week. Her boyfriend, aged 22, had a blood mercury level that was elevated (59 nmol/L).
It has been widely publicized that larger fish such as shark, swordfish and fresh or frozen tuna contain high levels of mercury. A recent report revealed that in 10 of 11 patients referred to an occupational health referral clinic in the US because of elevated mercury levels thought to be due to environmental or workplace exposure, those levels were instead due to dietary intake.5 Health Canada, in May 2001, recommended that such fish be consumed not more than once per week.6
Environmentally acceptable levels of mercury are based on what would be unlikely to cause health effects even in high-risk situations such as pregnancy. Nonetheless, in this era of cholesterol anxiety, many health professionals encourage seafood consumption. Physicians need be aware that toxic mercury levels can result when exposure occurs at higher than recommended levels.
John Sehmer General Practice – Industrial Medicine Vancouver, BC
References
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