Study designs of evaluations included in the review
Randomised controlled trials (RCTs) were eligible for inclusion. Observational follow-up studies that followed on from two of the included trials were also included in the review. The duration of the trials varied from 4 months to 2 years. The duration of the two follow-up studies was to 18 and 39 months of age.
Specific interventions included in the review
Studies of infant formula to which n-3 long-chain polyunsaturated fatty acids (DHA) had been added with or without n-6 long-chain polyunsaturated fatty acids (ARA) were eligible for inclusion. In some of the included studies both DHA and ARA (from sources such as fish oil, egg lipid, algal oil and fungal oil) were added in various proportions, while in others only DHA was added. The time at which the intervention was started varied from immediately up to 6 weeks, while its duration varied from 17 to 51 weeks. All the studies were described as having a control or standard formula group; some also had a breast fed reference group. The control intervention used for randomised comparison of effects in the included studies appeared to be non-supplemented formula.
Participants included in the review
Studies of healthy, term infants were eligible for inclusion. Studies of pre-term infants and low birth weight newborns were excluded. The infants in the included studies were newborns of at least 37 weeks' gestation. Some trials excluded infants with milk protein intolerance or a family history of such.
Outcomes assessed in the review
Inclusion criteria were not stated. The outcomes of interest appeared to be growth and cognitive, neurological and visual development. The outcomes reported in the included studies were anthropometrics, the amount of fatty acids in the blood, visual acuity, neurodevelopment (Bayley Scales of Infant Development II), information processing or intelligence quotient or cognitive development, language skills, temperament and morbidity.
How were decisions on the relevance of primary studies made?
The authors did not state how the papers were selected for the review, or how many reviewers performed the selection.