To examine whether daily supplement of docosahexaenoic acid throughout the first year of life may speed up the achievement of gross motor development milestones in healthy infants, a total of 1160 healthy infants randomly allocated to receive throughout the first year of life daily oral supplement of vitamin D3 (400 IU) plus docosahexaenoic acid (20 mg) or vitamin D3 (400 IU) alone. Primary outcome measure: time of achieving gross motor development milestones. Secondary outcome measure: time of achieving early fine motor development milestones and language.

Inclusion Criteria:

• weight at birth equal or above 2500 g;
• gestational age between 37 and 42 completed weeks;
• single birth;
• absence of neonatal or birth abnormalities;
• Apgar score greater than or equal to 7 at 5 m;
• white parents.

Exclusion Criteria:

• presence of neonatal diseases requiring hospitalisation for longer than 7 days;
• unknown father;
• parents unable to understand the protocol requirements and to fill out the infants diary;
• infant already enrolled or selected for another clinical study.