I've been following the fish oil story for a while, ever since a
href="http://archpsyc.ama-assn.org/cgi/content/abstract/56/5/407">small
study in 1999 showed potential benefit in patients with
bipolar disorder. The theoretical basis for the study was
that omega-3 fatty acids alter neurotransmission in a way that is
similar to lithium and valproic acid. A
href="http://ajp.psychiatryonline.org/cgi/content/abstract/163/6/969">recent
review in Am J Psych. Says the same thing that most other
articles have said over the past seven years:
CONCLUSIONS: Deficits in omega-3 fatty acids have
been identified as a contributing factor to mood disorders and offer a
potential rational treatment approach. This review identifies a number
of hypotheses and studies for consideration. In particular, the authors
argue for studies clarifying the efficacy of omega-3 supplementation
for unipolar and bipolar depressive disorders, both as individual and
augmentation treatment strategies, and for studies pursuing which
omega-3 fatty acid, eicosapentaenoic acid (EPA) or docosahexaenoic acid
(DHA), is likely to provide the greatest benefit.
In other words, there is a lot of evidence, but so far no one seems
willing to come out and make a definitive statement that the stuff
works. Everyone says that more studies are needed.
This is a difficult thing to establish, for a variety of reasons.
For one, there are serious ethical problems involved in trying to study
an unproven therapy in a condition that can have serious consequences
if left untreated. Second, the placebo response rate tends to
be high, particularly for unipolar depression. Third, what we
really care about is the long-term course of the illness.
Results of short-term trials are interesting, but they do not
tell us what we really want to know the most.
Consequently, it is necessary to get a very large sample size, and
follow the patients for an extended period of time, in order to get
definitive answers. And since you cannot patent fish oil, the
financial incentive to do this is not great.
In practical terms, then, what is the clinician to do? If you
are committed to following an evidence-based medicine approach, you
obviously want to give preference to treatments that are
supported by high-quality evidence.
Still, the principles of EBM do not preclude use of treatments that are
only moderately or poorly supported. It's just that you have
to weigh various factors more carefully. One, you have to
decide if you are administering the treatment instead of an alternative
that has better support. Two, you have to decide if the
potential risks are justified, in the face of inadequate evidence for
benefit.
The first factor depends a great deal on the patient's prior treatment
history and the patient's preferences. The second, ideally,
will be based upon actual data.
For the most part, fish oild is thought to be safe. Now
there is an additional bit of evidence:
href="http://www.medpagetoday.com/PrimaryCare/DietNutrition/tb2/4753?pfc=101&spc=246">High-Dose
Fish Oil Called Safe During Pregnancy
PERTH, Australia, Dec. 21 -- High-dose fish oil supplements given
during pregnancy appear to be safe for the baby and even improve later
hand-eye coordination...
...Fish oil provides an extra dose of long-chain fatty acids essential
for normal neuronal and visual development, but no studies had been
done to evaluate whether high doses are safe for the fetus, the Perth
group reported online Dec. 20 in the Archives of Disease in Childhood
(Fetal and Neonatal Edition)...
...However, the children of women in the fish oil group had
significantly higher hand-eye coordination scores on the Griffiths
Mental Development Scale than those of the control group (114.0 versus
108.0, P=0.021). Despite adjustment for maternal age, maternal
education and duration of breast feeding, supplementation remained a
significant independent factor (P=0.008)...
They did find other positive effects, but none that was statistically
significant. They saw no discernible negative effects.
While this still does not constitute proof of safety, it does
provide us with a little more confidence that high-dose fish oil is not
bad for people.
I would not take this study as evidence that pregnant women should
start taking fish oil. Rather, they should stick to
established principles of good nutrition.
The reason this study is important to me, is that when we are forced to
work with evidence that is not strong enough for anyone to make
definitive statements of safety and efficacy, every little bit helps.
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There is a balance to be considered. A treatment that is risky or expensive requires cautious evaluation.
A treatment that is inexpensive, known to be good for other health effects, has no known dangers and is unlikely to be in conflict with other treatments (which should be considered as well) seems like a sensible precaution.
There are large populations that have eaten diets high in fish -- and hence, fish oil -- throughout their lives, giving plenty of opportunity to notice risks specific to such diet. And in fact we have noticed a risk peculiar to recent times, with regard to mercury. No, that is not a formal trial, and yes, taking a tablespoon of fish oil each morning is different from eating fish. Still, when it comes to general safety of a food, I'll take the experience of dozens of generations of various coastal populations against one or two short-term trials of something invented in the last couple of decades.