Preterm infant girls who received a high amount of dietary docosahexaenoic acid (DHA; an omega-3 fatty acid) had higher measures of neurodevelopment than preterm girls who received a standard amount of DHA, but this effect was not seen among preterm boys, according to a study in the January 14 issue of JAMA.
Infants born before 33 weeks' gestation are at high risk of developmental disorders and learning disabilities. An inadequate nutrient supply during the newborn period is believed to contribute to this poor developmental outcome, according to background information in the article. DHA deficiency is hypothesized to result in poor neurodevelopmental outcomes in preterm infants, but uncertainty exists about the benefit of dietary DHA.
Maria Makrides, B.Sc., B.N.D., Ph.D., of Women's and Children's Hospital and Flinders Medical Centre, Adelaide, Australia and colleagues conducted a randomized controlled trial to determine the effect of high-dose dietary DHA on neurological outcomes in preterm infants. The study included infants born at less than 33 weeks' gestation from five Australian hospitals. Of the 657 infants enrolled, 93.5 percent completed the 18-month follow-up.
The infants were randomized to high-DHA (approximately 1 percent total fatty acids) compared with standard DHA (approximately 0.3 percent total fatty acids) from day 2 to 4 of life until the infants reached their expected date of delivery. The infants received DHA from either breast milk or infant formula. Lactating mothers allocated to the high-DHA group were asked to consume six 500-mg DHA-rich tuna oil capsules per day to achieve a high breast milk DHA concentration. If supplementary formula was required, infants were given a high-DHA preterm formula. Mothers with infants allocated to the standard-DHA group were asked to consume six 500-mg placebo soy oil capsules that did not change the fat content or fatty acid composition of their milk.
To measure neurological development, the researchers used the Bayley Mental Development Index (MDI), which evaluates memory, problem solving, early number concepts and language. They found that the average MDI score did not differ between the high-DHA and standard-DHA groups, but that the MDI score among girls fed the high-DHA diet was significantly higher than among girls fed the standard-DHA diet, while the MDI score among boys did not differ between groups.
"The lack of responsiveness of boys to the intervention is puzzling, and the reasons are unclear …," the authors write.
The MDI score among infants born weighing less than 2.8 lbs. and fed a high-DHA diet until the expected date of delivery was higher than that of infants fed standard-DHA diets in the unadjusted comparison, but did not reach statistical significance following adjustment for gestational age, sex, maternal education, and birth order. The MDI score of infants born weighing at least 2.8 lbs. did not differ between groups.
An evaluation of movement abilities found no significant difference between groups.
Additional analyses indicated that, overall, fewer infants had significantly delayed mental development with high-DHA diets compared with standard DHA and that there were fewer girls with mild and significant mental delay in the high-DHA group relative to the standard-DHA group, but there were no differences among the boys.
"Infants ranged in gestational age from 23 to 33 weeks and, thus, had a range of nutritional stressors, organ immaturity, and [illnesses]. Despite this, the intervention was sufficiently robust to consistently elicit an improvement in the MDI scores of girls and may point the way for higher-dose interventions in future studies. Given the lack of an alternative therapy for cognitive delay in this group of infants and the apparent safety of the current dose of DHA, further studies are warranted," the authors conclude.
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