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STEVE INSKEEP, host:

It's MORNING EDITION from NPR News. Good morning, I'm Steve Inskeep.

Today in Your Health, we'll consider some benefits and dangers of using seafood as brain food.

If you're eating fish, it's likely you're also eating the omega-3 fatty acids found in those fish. And those acids have their benefits for the developing brain. Good for kids, but pregnant women and new moms are advised to eat limited quantities due to concerns about mercury.

However, it's possible to get these omega-3s without ever eating fish. And if you want to find out how, you need to go to an algae lab, a place where algae is grown in big steel vats.

NPR's Allison Aubrey explains.

ALLISON AUBREY: Thirty-six-year-old Casey Lippmeier is a New Englander who grew up eating lots of fish. These days he still loves a good Maine lobster, but now as senior scientist at the Martek Corporation he gets most of his omega-3s from a source that's grown right in his company's laboratory, which is kept under lock and key.

Mr. CASEY LIPPMEIER (Martek Biosciences Corporation): I have some trouble with this lock occasionally, so make sure I get this right here. They may have put the code on it. Let's go through the other door.

AUBREY: Inside there are hundreds of samples of green algae jiggling around in small glass shake flasks. What makes them valuable to Martek is the fact that many of these algae strains have abundant supplies of a particular form of omega-3 fatty acid called DHA, which is exactly what's found in fish oil. Lippmeier explains that fish do not make DHA; they get it through the food chain.

Mr. LIPPMEIER: So the algae are very, very small, and so of the large fish can't eat algae directly. So you know, the algae are eaten by other really small things - cocopods, rotifers, things like that, and then, you know, those will get eaten by slightly larger fish, et cetera, et cetera, et cetera, until you get up to the biggest fish all.

AUBREY: In the wild, big fish that provide lots of DHA can also build up contaminants such as mercury or PCDs in their tissue. So as Lippmeier sees it, Martek is producing a pure supply of DHA by fermenting algae in big, steel brewer tanks.

Mr. LIPPMEIER: These tanks, we know all the ingredients that go into it and so we can assure about what all the ingredients that are coming out of it.

AUBREY: When Martek's biologist first came up with the idea of growing algae to produce DHA supplements, no one seemed to notice. But in 2002, manufacturers of infant milk formula began adding Martek's DHA to the formula. The decision was based on clinical trials that found infants who were fed a DHA supplement did better on cognitive tests than babies who were fed a regular formula.

Emily Oken is a researcher at Harvard Medical School. She says the most significant effect of the DHA seemed to be improved visual processing.

Ms. EMILY OKEN (Researcher, Harvard Medical School): So looking at whether infants can recognize a new face compared to one they've seen before, and they seem to do that quickly.

AUBREY: Oken says these findings clearly supported babies getting more DHA. But the research did not find that the benefits lasted as the infants became toddlers.

So it could be that the benefits of extra DHA are short-lived, or it could be that what a mom eats when she is pregnant may be more important than what the child eats once he or she is born. Oken says not knowing for sure is just part of the scientific process.

Ms. OKEN: You know, in science there has to be sort of a preponderance of evidence and that doesn't come from just one study.

AUBREY: Figuring out whether extra DHA helps you think better may take time, but for pregnant women and developing babies it's absolutely crucial, because the brain is literally made out of DHA.

Norman Salem is a neurobiologist with the National Institutes of Health. He explains that DHA makes brain membranes flexible, which is important. Animal studies show that when DHA is drastically reduced in the brain, processing slows.

Mr. NORMAN SALEM (National Institutes of Health): From neuron to neuron or from the retina to the brain, those signals, they'll still go, but they may be slower and not as intense.

AUBREY: Human populations have always consumed omega-3s from a variety of sources. They're found in eggs and more heavily concentrated in eggs laid by chickens who eat plants rich in them.

Organ meats such as liver and brains, though not popular in the modern American diet, are abundant too. Nuts and seeds such as walnuts, flax seed and canola oil are good supplies, though the body has to convert these plant sources to DHA. And since fish are loaded with lots of DHA and protein, Harvard's Emily Oken has made fish the focus of her work.

Ms. OKEN: The exciting thing about this field is that people are really looking now finally at, you know, what is the effect of fish consumption?

AUBREY: Oken and her colleagues are among the first to closely track the risks and the benefits of fish eating in a group of Americans.

Eight years ago, they recruited hundreds of pregnant women who shared details of their diets and gave blood samples so scientists could see exactly how much mercury was in their blood. When the children of these women turned three, researchers evaluated them using something called the Peabody Picture Vocabulary Test that correlates with verbal IQ.

It turns out that fish intake was associated with a two-point higher score. But children whose mothers had the highest blood mercury levels scored about four points lower on the test.

So while the differences are measurable, Oken says there are not huge swings.

Dr. OKEN: The kinds of exposures that people are getting from eating fish are not likely to take a child who would have been a genius and make them below average. These are very subtle effects for any individual child.

AUBREY: But Oken says if you look at the whole population, these subtle changes could influence the number of children on the threshold of being mentally retarded; or on the other side of the spectrum, the number of children within reach of being considered academically gifted.

Oken's study is ongoing and she'll continue evaluating the children through the school years to better understand how these associations between fish consumption and mental development hold up.

INSKEEP: We've been listening to NPR's Allison Aubrey. And Allison, I want to ask one more question that you allude to in a piece, but just asking it directly. If people are buying these fish oil supplements, which they think are good for them, do they have to worry about mercury?

AUBREY: Actually, no. There is no concern about mercury in these supplements and that's because there's a sort of standard refining and distillation process. So when manufactured by the oil, it's in a triglyceride form and they convert it to this form called ethyl ester. They distill it. And when they distill it, they leave behind the mercury and the other contaminants.

Some groups have tested these - Consumer Reports, consumerlab.com - and they've analyzed many brands and have found there are no problems.

INSKEEP: So the stuff is safe. The stuff is an essential building block for your brain, although it has varying benefits at varying times. I guess the next question is - are all different kinds of this fish oil or other kinds of supplements the same?

AUBREY: So supplements that are labeled as fish oil, they'll have a combination of DHA, which we've just heard a lot about, and EPA. These are the two long-chained polyunsaturated fatty acids. And the DHA is considered the beneficial one. The same is true of cod liver oil, has the DHA and EPA.

Now, if you're buying something that says omega 3 on the label...

INSKEEP: Mm-hmm.

AUBREY: ...that means it will probably have a third type of polyunsaturated fatty acid. This is called ALA, or alpha-linoleic acid. And this is the fatty acid that comes in nuts and seeds and in the membranes of a lot of dark leafy plants.

Now, there's also the issue of how the body absorbs the supplements versus sort of eating fish. And the researchers I spoke with tell me that from the limited studies that have been done, they say it's the same molecule - the DHA is the same molecule, whether it's in fish or if it's in a supplement, so that the body would take it up the same way.

INSKEEP: You mentioned that all of this is coming from algae, it's coming through fish and getting to people. What if you go to the source? Can you go to the source and just eat algae, if that sounds tasty?

AUBREY: Well, I guess you could if you found the right pond scum and you knew it had DHA in it.

But Martek, where we visited earlier, they actually make their own algae supplements that are sold just as supplements, and they also sell it to lots of manufacturers who are now adding it to orange juice, eggs, buttery spreads, you name it. There's a lot of DHA supplement in foods now. And the reason, again, is that not everybody has latched onto this idea that it's good for brain health, but there is a very strong body of evidence linking them to heart health.

INSKEEP: NPR's Allison Aubrey has been helping us to trace a dietary supplement to one of the smallest creatures among us. Thanks very much.

AUBREY: Thanks, Steve.

INSKEEP: You can get the government's full recommendations on which fish are safe to eat and which are not by going to npr.org/yourhealth.

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