The long tem study has been conducted on over 770 children, mothers of whom were exposed to mercury during intra uterine development. Majority of the mothers belonged to areas close to the Indian Ocean and ate 10 times more fish than Americans.
The large number of children born with birth defects in Japan (around 1950s) due to the large scale dumping of toxic mercury waste by a Japanese factory, raised concerns about the teratogenic effects of acute mercury exposure.
Very little is known at the present about the effects of chronic, low level of exposure to mercury. The researchers therefore designed a study to analyze the effects of mercury on fetal development and the long-term effects of the same. The determination of mercury content of the mother's hair provided a good indication of the level of exposure to mercury.
No significant side effects were however documented even when the child had reached 16 years of age. The researchers who are surprised about the finding hypothesize it could be due to negligible amount of mercury consumed through seafood. It is also believed micronutrients present in fish could counteract the ill effects of mercury exposure. It may infact aid in normal brain development in ways that are not completely understood.
Although several such studies have been conducted, debating about the advantages and disadvantages of eating fish, more studies are clearly indicated to accurately analyze the benefit-risk ratio. The FDA recommends limited intake of fish (fresh tuna, canned tuna, swordfish, shark) to maintain a perfect balance between micronutrient consumption and mercury exposure.