ADHD symptoms were noted when the children were 5 years old . This research shows associations , not cause - and - effect . Fish consumption is not independently linked to the symptoms . However , salmon and tuna are more likely to contain high levels of mercury .
ADHD symptoms were noted when the children were 8 years old . This research shows associations , not cause-and-effect . Fish consumption is not independently related to ADHD symptoms . Shark , swordfish and tuna are more likely to contain high levels of mercury .