the investigators carried out a prospective randomized controlled double blinded trial in order to study nutritional supplements for preterm infants <1500 grams and/or <32 weeks gestational age (GA) who were born in clinical University Hospital of Santiago de Compostela (CHUS). They were enrolled for a period of 14 months (from July 2011 to August 2012) and followed up from birth until 2 years of age. Milk formulas were provided either as adjunct to insufficient amount of breast milk, or as full formula feeding. Breastfeeding was actively encouraged. Patients were randomized into one of the two formula groups, depending on the type of formula they were to receive. Group A's formula was supplemented with DHA (0.3% of all fatty acids) and AA (0.6%) with an ω-6/ω-3 ratio of 2/1. Group B's formula was supplemented with DHA (0.3%) and AA (0.3%) with an ω-6/ω-3 ratio of 1/1.