Omega-3 Fatty Acids in Your Child’s Brain

Politics

Besides being a noteworthy problem, methylmercury is undoubtedly used as political propaganda, which means much of what you hear about it is exaggerated or distorted.  Omega-3 Fatty acids aren’t quite like that, but there are still many economic and political interests at work.  Let’s start with the most obvious ones first:

• The Supplement Industry.  Omega-3 fatty acid supplements are widely sold as dietary supplements.  People usually buy dietary supplements to improve their health.  But, do they really?
• The Fish Industry.  Most people eat fish because it is a food they like.  However, many fish contain high levels of Omega-3 fatty Acids, and it doesn’t hurt if people think there is an extra health benefit.  People might pay more for it (there is a limited supply).  Furthermore, a little anti-propaganda might help when someone starts talking about methylmercury of some of the other contaminants found in fish.

However, in addition to normal commercial salesmanship, there is a lot of other stuff going on in the world of political advocacy too:

• Wicked Tuna.  Ocean caught fish are wildlife.  Since many fishing areas are overfished, many species occur in fewer numbers that they used to.  There are advocates who think they can be protected by advising you they are harmful.  Large predatory fish like tuna tend to have higher levels of mercury, so some advocates think maybe they can be protected by warning consumers of the risks of mercury.  It doesn’t work -- as you might suspect, all the fish caught get eaten anyway.
• Organic Food.  On the other hand, some people are more worried about whether or not what they eat is natural.  There is no doubt about it, farmed fish is less natural than what the nets bring up out of the oceans.  Of course, the chickens, pigs, and cows that end up in the grocery store aren’t very natural either – they are specifically raised so that you can eat them.  So, the thinking goes, you should eat more wild caught fish even it has more mercury.
• Sustainability.  You can’t really protect wildlife by eating it, but advocacy groups have tried to combine what are really competing interests into one measure.  Since it is not farmed, low in mercury, and is a good source omega-3 fatty acids, wild-caught salmon is the best fish on this scale.  But if everyone thought wild-caught salmon was the must-have fish then it would get expensive and perhaps scarce as well.  The Environmental Defense Fund does list fish that are Eco-friendly separately from Eco-friendly & healthy, but they won’t tell you that farmed salmon is a good source of omega-3 fatty acids that is low in mercury because they think aquaculture is bad for the environment.
• Multivariate Advocacy.  There are many factors that influence neurobehavioral development in children.  Trying to sort it all out is next to impossible, especially when many of the factors are correlated.  For example, are some children smarter because they have chemical X or because they don’t have chemical Y)?  Or, even though there is no causal relationship, do they happen to have chemical X (or not Y) because their parents are smarter?  Sometimes, you just can’t be sure.  When X and Y are correlated (e.g. methylmercury and omega-3 fatty acids), it’s even harder.   Now, to get to the political part of this, many experts are also advocates for the issue they just so happen to be studying.  So, it seems that if you are a mercury expert, you can argue that the mercury effects are bigger if there are beneficial effects that counteract the mercury effects in some way (Choi et al, 2014).  Maybe they are right, but then again, maybe they are just trying to make methylmercury look worse than it is by claiming that the benefits of fish consumption are bigger than they are.

So, all those competing interests often have a way of creeping into scientific evaluations.  I’ve done my best to sort it all out, and my bottom line is described below.

Science

As a brief overview, the key points for a dose-response relationship for omega-3 fatty acids consumed by a pregnant women and the neurobehavioral performance in the child are as follows :

• The best evidence comes from epidemiological studies that compare neurobehavioral performance in the children of mothers with different levels of fish consumption.  There are two problems with this.  First, if there is a beneficial effect, it may be the result of something else in fish.  Second, fish consumption my mothers and children are correlated, so it is hard to tell whether an apparent beneficial effect come from the mother eating fish or the child eating fish.
• The evidence for a positive effect from fish or omega-3 fatty acids is not as strong as the evidence for a negative effect from methylmercury.  There are no epidemics like Minamata and Iraq that provide conclusive proof of an effect.  
• The best quantitative evidence all comes from a British population study where even though there is a clear association, it is not possible to be sure that the association is causally related. 
• The apparent effects from fish or omega-3 fatty acids on neurobehavioral performance are largely restricted to verbal and cognitive performance.  There is no evidence for a benefit on motor skills.
• If there is an effect, then the beneficial effect on neurobehavioral development in general, is much bigger than the mercury effect, at least with low to moderate levels of fish consumption.I have three different dose-response models for neurobehavioral benefits from maternal fish consumption, which are designed to be paired with some of the key dose-response models for methylmercury.  The paired models were used to correct for the impact of methylmercury on the overall effects from consuming fish.

Unlike some of the methylmercury dose-response models (i.e. the developmental milestone models), the estimates are entirely based on population averages – there is no attempt to account for possible variation in the magnitude of the response among different individuals. 

Additional technical details can be found in the FDA fish risk-benefit analysis (USFDA, 2014).  However, I have modified what that document describes by adding an additional probability tree that allocates probabilities to the following mutually exclusive propositions:

1. There is a beneficial effect on neurobehavioral development from maternal consumption of fish, and it is attributable to omega-3 fatty acids.
2. There is a beneficial effect on neurobehavioral development from maternal consumption of fish, and it is attributable to other nutrients in fish.
3. There is no beneficial effect on neurobehavioral development from maternal consumption of fish.

As a result of that modification, instead of six alternative models where propositions 1 and 2 are kept separate, there are only three.   Also, since it is a key issue and the probabilities assigned to each proposition reflect my subjective evaluation of the literature, I have made it easy to change.

Software

The dose-response relationship between fish consumption and neurobehavioral development in demonstrated with this Excel workbook:

PUFA DR_Function.xls

References

Choi AL, Mogensen UB, Bjerve KS, Debes F, Weihe P, Grandjean P, and Budtz-Jørgensen E (2014).  Negative Confounding by Essential Fatty Acids in Methylmercury Neurotoxicity Associations.   Neurotoxicol Teratol. 42: 85–92.

Daniels JL, Longnecker MP, Rowland AS,  and Golding J (2004).  Fish intake during pregnancy and early cognitive development of offspring.  Epidemiology 15:394-402.

Hibbeln, J.R., Davis, J.M., Steer, C., Emmett, P., Rogers, I., Williams, C., Golding, J. (2007).  Maternal seafood consumption in pregnancy and neurodevelopmental outcomes in childhood (ALSPAC study):  an observational cohort study.  Lancet 369:578-85.

U.S. Food and Drug Administration (2014).  Quantitative Assessment of the Net Effects on Fetal Neurodevelopment from Eating Commercial Fish (As Measured by IQ and also by Early Age Verbal Development in Children).  

Official Post Soundtrack

Belew, Adrian (1983).  Fish Head.  In: Twang Bar King, Track 11.

Post Notes

This is Thesis Post #59, and the fourth in the series that develop a risk-benefit model for fish consumption tailored to individual consumers.  The fifth and final part of the series will put the first four parts together,