Does tuna make you dumb?
No. While tuna contains a small amount of methylmercury, studies have yet to find that such low levels found in tuna (especially canned "chunk light" tuna, which has the lowest of all tuna varieties), creates any symptoms of mercury poisoning, which include cognitive deficits. In fact, some studies have found that children born to mothers which consumed the greatest amount of fish and omega-3 fatty acids during pregnancy tended to have higher cognitive performance than their peers. This suggests that any deficit caused by mercury in fish is either negligible or canceled out by the omega-3 content. It still doesn't hurt to be safe and choose high omega-3, low mercury fish products such as salmon instead of high mercury fish with less omega 3s, such as swordfish and tilefish.