Positive effects of postnatal DHA supplementation in term infants are typically seen above 0.20% total fatty acids as DHA (14
), but concentrations of DHA in human breast milk can vary well beyond these levels, suggesting that systematic tests of doses at higher levels are desirable. The analyses of data from infant psychophysiological responses and on the quality of attention at 4, 6, and 9 months showed significant and positive effects of LCPUFA supplementation on the quality of attention in infants from 4 to 9 months of age.
There were no Formula effects or interactions on the peak look variable from habituation. The age effect observed here for this variable has been routinely reported in prior research (33
) and is generally attributed to older infants' more rapid processing of stimuli during habituation (26
). The lack of any significant effects involving Formula here contrasts with prior results indicating sensitivity of look duration to LCPUFA status in preterm infants or to maternal LCPUFA status in full-terms (25
The proportion of time spent in SA, which is the phase of attention most strongly linked to active information processing in human infants (37
), was increased
relative to controls in the 0.32% and 0.64% DHA doses, but not at the highest (0.96%) dose. The finding of increased SA was observed across all ages at which the measure was taken (4, 6 and 9 months). Given that this improvement was not linearly related to DHA dose, we are inclined to posit DHA levels as the source of the effect on SA; since SA at the highest DHA dose was not statistically distinguishable from the two lower doses, however, the contribution of ARA cannot be definitively ruled out, as the power of the study may be less than optimal for comparing individual conditions to one another. If the effect is attributed to DHA, this would represent the first indication that higher doses of DHA may not incur proportional benefit. In a previous observational study, higher maternal DHA status at birth was found to be associated with lower look duration in later infancy (25
); within the context of those results, SA was also observed to be lower in infants from high-DHA mothers, which is what one would expect as look duration is reduced. However, in the previous study, DHA status was observed to reduce look duration, in the current one LCPUFA supplementation did not. We have observed that when look duration is reduced across or within sessions, the proportion of SA is reduced, and is generally displaced by OR (39
). This appears to be due to the fact that OR represents a latency to decelerate that is fairly constant; in briefer looks, OR takes up a larger proportion of looking, and essentially takes this proportion from SA. The increase in SA in the 0.32% DHA and 0.64% DHA formula conditions is interpreted as the maintenance of engaged cognitive processing in the context of equal amounts of looking; we see this as a positive benefit of supplementation. It is important to note that the recent results of a large longitudinal study show that infants who show reliable age-related decreases in look duration while maintaining high levels of SA across the first year show better performance on language and cognitive outcomes out to age 4 (40
LCPUFA supplementation also reduced infants' overall HR when measured during the administration of the visual attention task. The main emphasis of the original study was on dose effects for DHA; it was hypothesized that the three DHA-supplemented groups would vary. The fact that manipulation of DHA dose covaried with the presence of ARA in the formula (i.e., the control formula had neither DHA nor ARA) makes interpretation of this effect complicated, as the reduction in HR (relative to the control group) was statistically equivalent for each of the DHA dose levels. As such, we cannot definitively attribute this effect to the sole action of either of these compounds. The positive effect of LCPUFAs on cardiovascular health in rodents and human adults has been known for some time (41
), and there have been multiple reports of reductions in HR or increased HR variability as a result of some form of increased n-3 LCPUFA intake (43
Our finding here is also in accord with the results of a previous clinical trial of fish oil supplementation in infants (45
) and a preliminary report on an observational study of DHA intake in infants and toddlers (Pivik RT et al. 2008 Resting heart rate in infants and toddlers: Variations associated with early infant diet and the omega 3 fatty acid DHA. Forty-Eighth Annual Meeting of the Society for Psychophysiological Research, October 2–4, 2008, Austin, Texas, Poster 123), both of which report decreases in HR in relation to DHA status. The pathways through which LCPUFAs influence heart period are not definitively known, although candidate mechanisms include reduced oxygen consumption (46
), electrophysiological mediation of the heart rhythm (44
), or various forms of autonomic gating originating in the CNS (47
). The effect of lowering HR in adult populations is viewed as a positive health outcome and has been suggested to impart positive impacts on affective, cognitive, and behavioral outcomes (48
). HR declines systematically with age during infancy (31
) so the effect may also represent the acceleration of psychophysiological maturation.
In summary, the current findings add further experimental evidence for the positive health and cognitive effects of LCPUFAs in neurodevelopment in human infants. Further research will necessary to definitively dissociate the effects of AA from DHA on HR and SA; the current work may be constrained by limited power for these particular variables. Future reports will focus on the long-term implications of the improvements in attention observed with moderate DHA supplementation.