Fish, mercury and ADHD

I was browsing through EurekAlert the other day for new studies to blog about and came across this title: Low-level mercury exposure in pregnant women connected to risk in Attention Deficit Hyperactivity Disorder (ADHD). Now, I normally wouldn’t follow through on such an article, as I am: a. not pregnant, b. everyone knows mercury is toxic, so it shouldn’t be surprising that it causes problems. But the word ‘fish’ in the press release got my attention because I love eating fish and yes, I like to know what’s going on with my food, so I clicked on it and read the paper.

Got out of bed at 4am for super, super fresh sashimi. Best meal in my life - Tsujiki Fish Market, Tokyo. Copyright XiaoZhi Lim 2009.
Got out of bed at 4am for super, super fresh sashimi. Best meal in my life – Tsujiki Fish Market, Tokyo. Copyright XiaoZhi Lim 2009.

I figured it would just be another study about how pregnant women who ate more fish were exposed to more mercury which then increased their children’s risks of getting ADHD. But boy, was I wrong.

The study was actually more like two studies in parallel. Lead author Dr. Sharon Sagiv of the Department of Environmental Health, Boston University and the Department of Medicine, Brigham and Women’s Hospital, explained that they separated the studies by taking three sets of data: the first of pregnant women’s fish consumption, the second of pregnant women’s mercury levels in their hair and the third of their children’s ADHD behavior signs at eight years of age. The data for fish consumption and ADHD behavior, and the data for mercury levels and ADHD behavior were correlated.

Then it gets confusing. The results showed that pregnant women who ate more fish would have children with lower ADHD risk, while pregnant women who were exposed to more mercury would have children with higher ADHD risk.

And we all know that the more fish you eat, the higher your mercury levels because fish accumulates mercury.

What do we make of these results? I actually started to wonder how popular media might have represented this study as it just seemed like it would be something that gets snapped up. If I was pregnant, I would want to know if I had been eating something that might give my child ADHD.

I did a Google search on the keywords ‘prenatal’, ‘fish’ and ‘mercury’ about 36 hours after the public release on EurekAlert, and I was right – it was already all over popular media channels. ABC News, Fox News, CNN, TIME, Huffington Post, EmpowHer, Bloomberg… the list goes on and on. I went through several of them expecting that I would come across some grotesque misrepresentation or hype on the research. But I was wrong again. Sagiv told me that she”was pleasantly surprised to find that so far, the press has been getting the message across,” and I couldn’t agree more. As reported by ABC News:

Researchers say cutting fish out of the prenatal diet to avoid mercury exposure entirely is a bad idea, and pregnant women should look for fish that are low in mercury, such as salmon.

Check out how CNN did it:

… says Dr. Susan Korrick, M.D., the senior author of the study and an assistant professor of medicine at Brigham & Women’s Hospital, in Boston. “What really matters is the kind of fish you’re eating.”
…But Korrick and her coauthors had no information on what type of fish these women ate. And even if they did, there’s no reliable way to estimate which fish are high in mercury and which aren’t.

I do agree that there’s really no way to tell which fish is high in mercury and which isn’t.  It occurred to me to ask Dr. Sagiv in our interview if fish could be replaced by omega-3 supplements in pregnant women’s diets, but it seems that it would be “more likely that there’s a combination of nutrients from the fish” which is beneficial and not limited to just omega-3 fatty acids. For reference, American Pregnancy Association has a list of fish categorized by mercury levels, based on data from the FDA, NRDC and EPA. That raises the following questions – how was the data collected? How old was the data? Would the mercury levels in fish have changed over time? Would this increase demand for low-mercury fish and cause unsustainable overfishing in those species?

This will probably lead to something bigger than the scale of this blog post, but let me just end on a potential money-making invention. If something like a meat thermometer could be created for mercury – so it’d operate the same way except you poke the sensor into a raw fish and it comes up with a mercury reading – I’m sure many pregnant mothers will now be very interested in that product. Or at least, I will be, because I would like to be able to enjoy my fish without being afraid that my dietary preferences would have serious consequences, pregnant or not.