Human Data! Fish Oil During Lactation Reduces Cognitive Capacity at Age 7. Impairements in Processing Speed and Working Memory.

Supplemental fish oil:
Panacea or rat poison?

Well, I know you all love your fish oil. And you probably know I don't ;-) And this is why I am "happy" (yes, I am biased, here) to report the unfortunate results of a Danish study (Cheatham. 2011), which investigated the effects of moderate dose fish oil supplementation @ 1.5 g/d n-3 LCPUFA (vs. olive oil as placebo) during the first 4 months of lactation on the cognitive performance of 98 children. The data was obtained at the age of seven by a combination of an "age-appropriate Stroop task, and the Strength and Difficulties Questionnaire". The results were quite unequivocal:

[...] analyses including all participants revealed the speed of processing scores were predicted by maternal n-3 LCPUFA intake during the intervention period (negative relation) and maternal education (positive relation). Stroop scores indicative of working memory and inhibitory control were predicted by infant erythrocyte DHA status at 4 months of age (negative relation).

Thus, this is the first study to find direct evidence for the "negative effect" of supplemental fish oil in a critical phase of infant development on later cognitive abilities. This finding should however not really come as a surprise, as researchers Johanna Assis and Franocois Pouwer only recently sounded a note of caution (Assis. 2011) in their response to a the null results (+ negative effect on behavior scores), a fish oil intervention with 800 mg per day of DHA and 100 mg per day of eicosapentaenoic acid in pregnant women had produced (Makrides. 2010):

The absence of clear positive effects and the possible presence of negative effects in the children raise the question whether DHA supplementation is justifiable (not only during pregnancy, but in general).

Referring to previous reports of "insufficient" levels of, specifically, DHA Assis and Pouwer rightly state that "'low' levels may not necessarily mean 'deficient' levels, but may represent adequate or even adaptive levels".

All this stands in line with the negative outcome of studies on DHA as a potential anti-Alzheimers agent (Quinn. 2010), the fish oil induced increases in oxidative stress in athletes, measured only recently by Filaire (Filaire. 2010), and the negative results of the largest systematic review (15,159 titles and abstracts, 48 RCTs with 36,913 participants and 41 cohort studies) on the effect of fish oil on heart health (Hooper. 2006). All this research clearly suggests that, their triglyceride lowering effects aside, the beneficial effects of fish oil (the purported panacea of the early 2000s) are at least way overrated. Add to that the most recent finding and ask yourself why your body keeps burping up those fish oil gel caps - maybe, he knows better than you ;-)

Additional link (updated): Just to add to the above, ScienceDaily just reports Omega 3: What Is Good for the Heart May Not Be Good for the Prostate, Study Suggests.