Taking a fish oil supplement during pregnancy is linked to an increase in a child’s lean and bone mass by the age of six.
However, taking these supplements in the later stages of pregnancy does not bring an increased risk of overweight or obesity in this age range, suggest the findings of a large trial published by the British Medical Journal.
Studies in animals have shown supplementing the diet with fish oil during pregnancy affects the development of fat cells.
However, although trials in humans have shown pregnant women with a higher intake of fish oil supplements give birth to higher birth-weight infants, the impact on children later in life has been unclear.
A team of researchers based in Denmark and the United Kingdom oversaw a trial of 736 pregnant women who were randomised to receive fish oil or olive oil (used as a control) every day from week 24 of pregnancy week until one week after birth.
Height, weight, head and waist measurements, and body composition were assessed 11 times from birth to when the child turned six - and adjusted for age and sex.
Body composition was assessed using scans when the children were aged 3.5 and six years. The scans confirmed the higher weight was not the result of a higher fat percentage but reflected a proportional increase in lean mass and bone mass, suggesting the fish oil supplement stimulated growth.
At six, the scans showed children whose mothers had taken fish oil supplements while pregnant had 395g higher total mass, 280.7g higher lean mass, 10.3g higher bone mineral content and 116.3g higher fat mass compared with children of mothers who took the olive oil.