When American author Ayelet Waldman’s daughter was four she noticed something was not quite right. It was “nothing you would go to the doctor for”, Ayelet said in an interview with MedSchoolForParents.com, but her daughter was starting to forget things, like how to tie her shoelaces.
“She wasn’t progressing as fast, and her hair seemed more brittle than usual”. The signs were vague, but they were present. Ayelet’s daughter was a sophisticated four-year-old who “loved tuna sandwiches and sushi”. She would have on average 1 to 2 tuna sandwiches per week and had started eating tuna when she was two.
It was a bizarre but fortunate coincidence that Ayelet’s home used to have lead paint and her family received regular testing for lead poisoning. It took time but eventually Ayelet found out her daughter had high mercury levels. Like any concerned parent, the family sought medical advice, and it did not take long to find the culprit – it was those ‘innocent’ sandwiches. After eliminating tuna from her diet, the symptoms improved for ‘mercury girl’, and a few months later she was back to her usual self.
Ayelet’s story had a happy ending; her daughter did not suffer any long-term consequences of mercury poisoning such as tremors or sensory loss. But it does raise a concerning question- is it safe for children to eat tuna?
The Metal Hg
Mercury is a naturally occurring metal that is mined for a variety of purposes, such as for electric equipment and thermometers. Through the burning of coal and large-scale mining, mercury may be released into the environment.
Mercury (symbol Hg) has 3 forms - inorganic, elemental and organic. Elemental mercury is not absorbed in the gastrointestinal tract and only about 10% of inorganic mercury is absorbed through eating. Methyl mercury, a form of organic mercury, has a very high uptake into the bloodstream, approximately 90%.
Saltwater Finfish and Mercury
Mercury can be found in the environment where tuna swim and accumulate in the fish’s body while consuming food. The bigger the fish, the more mercury it will absorb, and tuna are big fish. The mercury in the environment from pollution is an inorganic form, however the tuna then converts the inorganic form of mercury to methyl mercury. Once in the fish, it binds to proteins, so trimming or cooking a fish will not really reduce the amount of mercury.
Why are we terrified of mercury?
How many times have you read Alice in Wonderland to your children, or sat down and watched the movie? We all laughed at the peculiar mad hatter and his eccentric ways. But there is an element of truth to this character. The Hatter was inspired by the phrase “mad as a hatter” which came about during the 1800s. Hat makers were exposed to mercury regularly during the manufacturing process and, as a result of the repeated exposure, had vivid hallucinations and became inattentive and excited.
Due to its chemical properties, methyl mercury collects in skin, hair, liver, kidneys and brain. It can even cross the placenta and affects fetuses and their development. It can cause devastating problems such as visual and hearing loss, psychiatric issues, loss of sensation and hair, memory issues, and difficulty walking. Naturally, no parent wants this to happen to their child.
Are the levels in canned tuna really dangerous?
There’s a lot of controversy surrounding canned tuna and mercury. Would someone stock the shelves of our local supermarkets with mercury rich products?
In a recent US study, 55% of all the canned tuna examined had levels above the US Environmental Protection Agency’s (EPA) safety levels. This leads to questions regarding the regulation of canned tuna. Certain types of tuna have been shown to contain higher mercury content compared to others. White tuna has higher levels compared to light tuna because it contains more of albacore tuna which are larger, whereas the light tuna is mainly skipjack tuna which is smaller.
How much tuna can my child eat?
The US EPA recommends 0.1mg/kg of child’ weight per day of tuna with a mercury content of 0.619ppm. This is around 75 mg of tuna every 19 days for a 25 kg child. However, the EPA’s guidelines are controversial. Dr Hightower, a San Francisco physician with an interest in mercury poisoning, discusses some of these issues in this video.
Ultimately, there are a lot of benefits for children who eat tuna, which are important for growth and development. As such, fish consumption should be encouraged in children. To stay safe of mercury, just favor smaller species of fish. If you are concerned about symptoms of higher mercury, follow Ayelet’s lead and consult a pediatrician.