It is no news
that essential fatty acids
are needed to maintain health. One of them,
Docosahexaenoic acid (much
better known as DHA), is particularly popular, as there is solid
evidence that it boosts protection from cardiovascular disease.
It is also no news that - shame on us - we still don't know much
of what exactly DHA, and other essential fatty acids, are used
for by the
A recent Australian study moves us another small step
deeper into that uncharted territory.
The study (Neurodevelopmental
Outcomes of Preterm Infants Fed High-Dose Docosahexaenoic Acid,
Makrides, Gibson et al., JAMA, 01/14/2009) investigated the
effect of supplementing DHA to preterm infants on their mental
development. In all, 657 babies born after less than 33 weeks of
pregnancy have been given either standard (about 0.3% of total fats)
or high DHA supplementation (about 1% of total fats) for the remainder
of the average 40-week term.
Their neurological development was
then evaluated at 18 months with Bayley Mental Development Index
(MDI), which scores baby's memory function, problem solving
ability, early number concepts, alertness, curiosity, ability to
do simple tasks for a reward, and language proficiency.
After six years, the study
arrived at somewhat intriguing conclusion: supplementation
didn't significantly help preterm boys, but did help girls. Girls
on high supplemental DHA had overall MDI score 99.1, compared to
94.4 score for girls on standard DHA. High-DHA group had the
incidence of mildly and significantly delayed mental development
of 9.9% and 1.4%, respectively, compared to 25%% and 9.7% in
the standard-DHA group.
Boys scored nearly the same in
both groups: 91.4 high-and 91.9 standard-DHA. High-DHA seemed to
be somewhat beneficial for underweight
babies (<1.25kg), with the incidence of mildly
delayed mental development about cut in half (16% vs. 32.6% for
high- and standard-DHA groups, respectively).
So, at the same time, the initial hypothesis - that
preterm babies have elevated need for DHA, being born
significantly before the end of the last trimester of gestation,
during which DHA supply to their brains peaks - has been both,
proved and refuted by study results.
Sure, we all know that girls and boys are
different: on average, girls have smaller brain, but it is more
complex and develops
faster (which is reflected by study's MDI figures). It could be
that boys didn't have as much use of the additional DHA simply
because their brain develops at somewhat slower rate. Still, it
is to expect at least some measurable positive effect, not zero.
The very structure of the brain - as well as functioning
- is also different for the two genders. Girls have better language related
functions, including reading, as well as social integration, while
boys get better at abstract thinking and spatial
coordination. Girls are (latter in life) affected only 1/4 as
often by attention deficit disorder as boys, and so on.
But we are talking here about a substance
needed for the
basic body structures and functions.
It is not likely that
boys simply burned most of the extra DHA for energy, due to
their faster metabolism, as the authors hypothesize. If anyone,
they should give more respect to human body: it is much smarter
than to burn - for the lousy 9 calories from about 1g of extra DHA
daily - what is needed for vital cellular functions. Rather,
they should turn to the possible study shortcomings, making its
final results less reliable.
don't have to look far to find them. Authors themselves state
that study results were "robust" enough to be interpreted as
positive - even if only for girls significantly - despite wide
variations in what we can generalize as the degree of
of baby participants (the authors address it more specifically
as substantial differences in gestation period - 23 to 33 weeks
- nutritional stressors, organ immaturity and illnesses).
other words, it was a random, uncontrolled factor in the study;
isn't it possible that this was influencing how babies were
doing, independently of DHA supplementation?
Of course it's possible. In fact, this is exactly
what another study (Morris et al., Journal of Pathology
2002) implies. The study followed 96 high-risk and 137 low-risk
pre-term infants, as well as 136 full-term infants at 6, 18, 30,
42 and 54 months of age (high- and low-risk levels were
determined according to the degree of present medical
complications). It concluded that the two most important
predictors of neurological development, measured by TCR (motor
tone, coordination and reflex) score, were the
of medical complications and gender,
which were more
consistent predictors than the third main factor, gestational
While the TCR is narrower in scope than
MDI in assessing neurological function, there is clear
correlation between the two. It is not to expect that the medical
risk level is the major factor for the former, and insignificant
for the latter. Thus, if the incidence of medical complications
among babies in all four primary groups of the Australian study
(DHA supplemented girls and boys, and standard-intake girls and
boys groups) wasn't at least roughly similar, it would very
likely induce bias in study results.
Another possibly influential factor that this study indicates
stems, again, from the difference in the
rate of brain
development between girls and boys. Morris et al.
established that the initial differences in the level of
neurological development tend to lessen going from 6 to 18
months of age, as infants that were behind developed at a faster
rate in this period. However, as more refined movements were developing, the
difference in the level of neurological development widened
In other words, girls in the Australian study
could have shown more of a difference in their neurological
development in part due to being at a more advanced level than
boys. This could have been neutralized by testing girls and boys
not at the same age, but at a similar level of their average
development; such balancing of all relevant factors should be a part
of study design.
But that is still only
wishful thinking. A crucial factor routinely neglected in 99% of medical
studies - with no justifiable reason - is
of the participants. It depends not only on their nutritional
intake, but just as much on individual metabolism processing
that intake. If one single nutrient, DHA, according to the
researchers, may have the power to significantly affect brain
how about all the rest of them?
Factors that should be controlled in this type
of study also include socioeconomic status, parents education,
both general and health and nutrition-related, genetic
inheritance, familial environment, as well as the always present
chemical environment. High exposure to
(phthalates), for instance, can interfere with fatty acid
metabolism, resulting in low DHA at the cellular level.
Sure, a study
controlling all relevant factors would be both, more complex and
more expensive. Funding constraints are often to blame for
compromises in this respect. But as long as we settle with
compromised medical studies, we'll keep getting these
unreliable, confusing, often contradicting results.
As for the DHA, it is no news that it
plays important role in development, as it does latter in life.
But so does host of other nutrients.
It is only logical that preterm babies have increased need for
DHA, but it certainly includes other nutrients as well. If we are to single out
the greatest value of this Australian study, it is in turning
our focus to what really matters for health.
And it ain't