Generally speaking tinned tuna has less mercury than "fresh" tuna steaks because the ones in the tins are generally smaller younger fish and hence have less mercury concentrated in them (about half on average). Canned tuna still has a lot more mercury than canned salmon and sardines but is ok as long as you don't have too much of it. A 60kg pregnant women can have up to 200 grams of canned tuna per week as long as she doesn't eat any other fish that week. I did some examples below in the summary.
Those flavoured sandwich tuna tins are often only about 50% fish - check on the label. You only need to count for the actual amount of fish in the can. 2 of those small flavoured tuna tins per week is fine even with another serve of low-mercury fish like salmon - this would still be below the recommendations set by the US EPA (Environmental Protection Agency) for pregnant women. The EPA standard is the strictest one and has a built in safety factor of 10.
If you are after those good Omega-3's, salmon and sardines have higher amounts of these compared to Tuna, and as a bonus, about 1/4 to 1/10th the mercury concentration (on average...they'll all be different). Shark, swordfish and marlin and orange roughy should just be avoided as they can be 10 times worse than tuna...
Mercury levels are an accumulative thing, the half life of mercury in your body is about 10 weeks. So if you eat a fish now, half of that mercury will be still inside you in 10 weeks. 10 weeks after that, a quarter of it will be in you and so on.
As you can tell I looked into this a lot...
-----"The Science"-----
The EPA's recommended "limit" for pregnant (or trying) women is 0.7ug of methylmercury per kg of bodyweight per week (but this is pretty conservative so don't stress if you go a bit over). "ug" is millionths of a gram.
So for a 60kg woman you can have (0.7 x 60) ug of mercury per week:
42ug per week for a 60kg woman
- Canned Tuna contains on average 19ug mercury per 100 gram serve
- Canned Pink Salmon contains about 3ug per 100 grams
- Fresh Salmon (Scottish - probably "worse" than tasmanian) contains about 5ug per 100 grams
- Fresh Tuna steaks (at least ones purchased in England) average about 40ug per 100 grams
- Swordfish and Shark contain as much as 280ug per 100grams!!!
All of these can vary widely, these are just averages I got from an English analysis from 2003.
----"The Summary"----
So eating 200 grams of Canned Tuna in a week will give you 38ug which is a bit below a 60kg woman's limit. You'd have to eat more than a kilo of Canned Pink Salmon to get near the limit. A 140gram fresh tuna steak would put you somewhat over the limit - try to avoid it if you can. But don't forget the EPA standard is pretty conservative. You will get a little bit of mercury in other parts of your diet too but fish will be the primary source.
I haven't done all the details here to keep it simple, for example you absorb about 95% of the methylmercury in fish, 5% passes through.
Hi guys,
I have a question about tuna fish. I love tuna and usually eat tons of it but when I found out I was preg I read somewhere that it contains alot of Mercury, although I think this is more fresh tuna and not so much tinned. So I cut down on my tuna intake (1-2 sml flavoured tins a week) but in this months "Pregnancy and Birth" there is a list of Pregnancy Superfoods and one of them is Oily fish such as Salmon, Trout, Mackerel and TUNA!!! It doesn't even mention mercury or limiting your tuna intake!!!
Can anyone help???
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