Pregnant women, nursing mothers and women thinking about getting pregnant should not eat more than 12 ounces of tuna and other fish per week, says a draft advisory from the Food and Drug Administration and the Environmental Protection Agency.

In the past, the FDA had warned pregnant women against eating big fish (shark, swordfish, king mackerel and tilefish) because they contain high levels of mercury.

The FDA advisory says mercury levels in tuna vary, and that tuna steaks and canned albacore tuna generally contain higher levels of mercury than canned light tuna.

Mercury is a neurotoxin that can harm an unborn child’s nervous system if eaten regularly. “Exposure to it from eating contaminated fish can lead to a number of neurological problems, including learning and attention disabilities and mental retardation,” Washington Post reports.

(via Washington Post)