There is some speculation that a dietary shift in favour of n-6 (omega 6) long chain polyunsaturated fatty acids (LCPUFA) over n-3 (omega 3) LCPUFA, may be linked to the increased prevalence of childhood allergic disease.

To further investigate, researchers evaluated whether dietary n-3 LCPUFA supplementation of pregnant women with a foetus at high risk of allergic disease reduced immunoglobulin E associated eczema or food allergy at one year of age.

Participants were recruited from the Docosahexaenoic Acid to Optimise Mother Infant Outcome (DOMInO) trial, a double blind, multicentre, randomised controlled trial of n-3 LCPUFA supplementation, predominantly as docosahexaenoic acid, in pregnancy to evaluate symptoms of maternal depression and neurodevelopment of young children. A total of 706 infants of these mothers who were at high hereditary risk of developing allergic disease were followed up.

The intervention group (n=368) was randomised to receive fish oil capsules (providing 900 mg of n-3 LCPUFA daily) from 21 weeks’ gestation until birth; the control group (n=338) received matched vegetable oil capsules without n-3 LCPUFA. The primary outcome for the nested allergy follow-up at 1 year of age was diagnosis of immunoglobulin E associated allergic disease (eczema or food allergy with sensitisation).

The following results were reported:

• No differences were seen in the overall percentage of infants with immunoglobulin E associated allergic disease between the n-3 LCPUFA and control groups (32/368 (9%) v 43/338 (13%); unadjusted relative risk 0.68, 95% confidence interval 0.43 to 1.05, P=0.08; adjusted relative risk 0.70, 0.45 to 1.09, P=0.12).

• The percentage of infants diagnosed as having atopic eczema (that is, eczema with associated sensitisation) was lower in the n-3 LCPUFA group (26/368 (7%) v 39/338 (12%); unadjusted relative risk 0.61, 0.38 to 0.98, P=0.04; adjusted relative risk 0.64, 0.40 to 1.02, P=0.06).

• Fewer infants were sensitised to egg in the n-3 LCPUFA group (34/368 (9%) v 52/338 (15%); unadjusted relative risk 0.61, 0.40 to 0.91, P=0.02; adjusted relative risk 0.62, 0.41 to 0.93, P=0.02), but no difference between groups in immunoglobulin E associated food allergy was seen.

The researchers concluded that n-3 LCPUFA supplementation in pregnancy did not reduce the overall incidence of immunoglobulin E associated allergies in the first year of life, but did reduce the incidence of atopic eczema and egg sensitisation. Longer term follow-up is needed to determine if supplementation has an effect on respiratory allergic diseases and aeroallergen sensitisation in childhood.