Fish provides undoubted benefits within a balanced diet , but it is convenient to limit or avoid (depending on the risk group) the consumption of some species due to their high mercury content, which is especially dangerous for brain development. This is the reason why the Ministry of Health has updated its recommendations following European guidelines and now advises not to eat swordfish, shark, bluefin tuna and pike until 10 years of age , to lactating women and pregnant women. .
Mercury accumulates mainly in the largest fish because they are those that are located at the top of the food chain and feed on the rest of the small and medium-sized species that, in turn, have ingested the mercury that is deposited in the algae and plankton.
This heavy metal constitutes a powerful poison if a high amount is accidentally ingested, but its toxicity also has medium and long-term effects when small amounts are consumed continuously, which occurs through diet and mainly due to the ingestion of fish. .
Fetal development, the most critical period
“The most critical period for neurotoxicity of mercury is during pregnancy,” says Jordi Júlvez, researcher at the Barcelona Institute for Global Health (ISGlobal) , a center promoted by La Caixa. During this period, everything the pregnant woman ingests affects, for better or worse, fetal development and, especially, brain formation .
Research carried out by Júlvez’s team and other scientists around the planet reveals that prenatal exposure to mercury affects higher cognitive functions: memory, attention, IQ, learning …
After birth and, above all, as the child develops , the effects are less severe. Still, it has been seen that it can affect aspects such as reaction speed or fine motor skills .
Júlvez summarizes how mercury exerts its devastating action: “It accumulates in muscles and blood and can cross the blood-brain barrier “, which is in charge of preventing the entry of potentially harmful substances into the brain. What happens is that the body “confuses mercury with iron, which is very important for the brain, and allows it to enter the brain and even enter neurons .” Once it has entered the brain, it can lead to neuronal death , especially in the most critical period.
Francisco Botella, from the Nutrition Area of the Spanish Society of Endocrinology and Nutrition (SEEN), stresses that, once this metal enters the body, “the organism does not have a way of elimination, so it stays forever ” And there comes a time when the small amounts that we ingest throughout the time cause problems.
On the other hand, Júlvez and his team have verified the influence of genetic factors on vulnerability to mercury toxicity . Specifically, they have verified that up to 30% of the child population carries a genetic variant that can increase susceptibility to this substance during pregnancy.
Effects in adults
The brain of adults supports the neurotoxicity of mercury better, but it is not advisable to let your guard down because, in addition, other possible damages have been observed . For example, some studies show that it could increase the risk of cardiovascular disease and kidney toxicity was known and investigated before the effect on brain development, as Bottle notes.
In any case, Health recalls the benefits of fish and only advises avoiding the consumption of species with the highest presence of mercury until 10 years of age and limiting it until 14. As SEEN recalls, “within a Mediterranean diet pattern, It is recommended to eat more fish than meat, since at equal weight it has fewer calories than meat and provides healthier fats . Specifically, two to four servings of fish a week are recommended, also including fatty fish. ”
In the selection is the key
To avoid headaches and continue enjoying the flavor and health benefits of fish, experts advise avoiding or limiting (depending on the risk group) swordfish or emperor fish, bluefin tuna, shark (dogfish, shortfin mako, spiny dogfish, redhead and blue shark and pike).
Fortunately, there are many species with lower levels of mercury. Sanidad considers that the following species have a low mercury content : pollock, anchovy or anchovy , herring, cod, blue whiting, cockle, mackerel, squid, shrimp, crab, cane, coal or fireman, carp, chipiro n, chirla, clam, choco / cuttlefish / cuttlefish, Norway lobster, coquina, bream, sprat, prawn, horse mackerel, lobster, prawn , European sole , dab, tongue, sea bass, mussel, merlan, hake or whiting, razor clam, oyster, pigeon, flounder, squid, octopus , shrimp, Atlantic salmon, Pacific salmon, sardine , sardinela, sardinopa, plaice and trout.
The other species of fishery products not specifically mentioned in that list are considered to have an average mercury content .