Is Daily Consumption of Deep Sea Fish Oil Safe Amid Mercury Concerns? - Family Medicine

Dr. Wang Zhengzhong reply Family Medicine

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Hello: Recently, there have been reports in the news advising against the frequent consumption of deep-sea fish due to mercury concerns.
I have compiled related issues regarding fish consumption and potential poisoning, although this does not pertain to deep-sea fish oil.
However, as long as consumption is moderate and you ensure that the products have the approval number from the health department, as well as clear labeling of the company, manufacturing, and expiration dates, it should be safe.

Mercury poisoning can be classified into inorganic and organic mercury toxicity.
Inorganic mercury ingestion can frequently cause gastrointestinal mucosal damage and significant bleeding.
Patients may experience shock, kidney damage, and acute renal failure, with a small number resulting in death.
Long-term ingestion of low doses of inorganic mercury can lead to chronic interstitial nephritis, resulting in uremia.
Some individuals with specific sensitivities may also develop membranous nephropathy.
Fish that contain mercury, particularly large marine species such as sharks and tuna, may have elevated mercury levels.
Therefore, fish fins and flesh may contain significant amounts of mercury.
Inorganic mercury ions that enter fish through the food chain can be converted into organic mercury (methylmercury) by microbial action in the presence of vitamin B12, and can accumulate through the aquatic food chain.
Methylmercury can bind to fish proteins, and fish living in waters with trace amounts of methylmercury can accumulate it to very high concentrations, sometimes thousands to tens of thousands of times higher than the water concentration.
Of the mercury that enters animals through food, 90% is methylmercury.
The most well-known form of organic mercury poisoning is methylmercury poisoning.
Pathologically, metallic mercury is first oxidized to divalent mercury ions within red blood cells and liver cells.
At low concentrations, mercury ions initially bind to the -SH groups of proteins, and at higher concentrations, they bind to amino, carboxyl, and phosphonyl groups.
The pathological changes of organic mercury poisoning primarily affect the brain, characterized by damage to the central nervous system, with symptoms including progressive muscle weakness, vision loss, impaired brain function, and eventual paralysis, with some cases leading to coma and death.
Symptoms of mercury poisoning include:
1.
Acute mercury vapor poisoning: Symptoms such as weakness, nausea, vomiting, chills, salivation, diarrhea, chest tightness, and coughing can occur within hours.
Prolonged exposure may lead to interstitial pneumonia, damaging lung function.
2.
Chronic long-term mercury vapor poisoning: This can cause involuntary tremors in the limbs and changes in personality and behavior, including irritability, forgetfulness, shyness, agitation, depression, instability, and confusion.
3.
Methylmercury poisoning: The primary symptom is damage to the central nervous system.
Methylmercury can be absorbed through the gastrointestinal tract and accumulate in the brain, with major symptoms including visual disturbances, lack of coordination, sensory and hearing loss, weakness, joint pain, cognitive impairment, and involuntary tremors.
Severe cases may result in paralysis and death, and pregnant women exposed to methylmercury may give birth to malformed infants with cognitive deficits.
4.
Acute inorganic mercury poisoning: This can cause gastrointestinal mucosal damage and significant bleeding, leading to shock, kidney damage, and acute renal failure, with a small number resulting in death.
5.
Long-term ingestion of low doses of inorganic mercury can lead to chronic interstitial nephritis, resulting in uremia.
Testing: The normal urinary mercury level is 0.25 umol/L; levels above this indicate mercury accumulation in the body.
Mercury levels in hair can reflect past mercury exposure.
Normal hair mercury levels vary by region and dietary habits.
Hair mercury levels of 400-500 µg/g are often associated with neurological symptoms, while asymptomatic individuals typically have levels between 50-200 µg/g.
Hair mercury levels correlate linearly with blood mercury levels; a hair mercury level of 50 µg/g corresponds to a blood mercury level of 200 µg/L.
Medical and nursing care:
1.
The primary treatment for mercury poisoning involves chelating agents such as BAL, DMSA, and Penicillamine.
2.
In cases of acute inorganic mercury poisoning, hemodialysis may be beneficial.
3.
There are no specific antidotes for methylmercury poisoning; however, taking resin (polythiol resin) may help bind methylmercury in the intestines, blocking its reabsorption through the enterohepatic circulation.
Case study: At Taipei Veterans General Hospital, a rare case of chronic mercury poisoning was reported in a family of five, where four members suffered from mercury poisoning due to long-term consumption of mercury-contaminated fish.
The only unaffected member was a one-year-old child, who consumed less fish.
The housewife participated in a hair mercury testing organized by an environmental protection agency and discovered high hair mercury levels.
She had been feeling fatigued, frequently catching colds, and experiencing nasal allergies, prompting her to undergo blood tests, which revealed a blood mercury level of 80 ppb (parts per billion), four times the acceptable limit.
Currently, there are no established blood mercury standards in Taiwan, but the toxicology lab at Taipei Veterans General Hospital considers a blood mercury level of 20 ppb as acceptable, a threshold that 90% of the population can meet.
In contrast, many international toxicology labs set the acceptable blood mercury level at 10 ppb.
The physician at Taipei Veterans General Hospital requested that the fish purchased by the housewife be sent for testing, revealing total mercury levels ranging from 0.3 ppm (parts per million) to 0.9 ppm, with methylmercury accounting for approximately 80% of the total mercury, which poses the greatest risk to human health.
It is generally accepted that levels exceeding 0.5 ppm are considered high, leading the doctor to suspect that fish consumption was the cause of the problem.
The health department has set a standard for migratory fish species, limiting methylmercury content to below 2 ppm.
After realizing the issue with fish consumption, the entire family went to the hospital for blood tests, revealing that the husband and two preschool-aged children all had blood mercury levels exceeding the acceptable limit, with the children's levels reaching 100 to 200 ppb.
Children are more sensitive to mercury, and due to their smaller size, their blood mercury levels can be significantly higher than those of adults.
The children exhibited hyperactivity at school and delays in speech development.
After more than six months of avoiding fish and receiving chelation therapy, the symptoms of the husband and wife have gradually improved, while the two children are still undergoing follow-up treatment.

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Reply Date: 2008/07/01