C C Grant, J Crane, E A Mitchell, J Sinclair, A Stewart, T Milne, J Knight, C Gilchrist, C A Camargo

Vitamin D has immune modulating effects. We determined whether vitamin D supplementation during pregnancy and infancy prevents aeroallergen sensitisation and primary care respiratory illness presentations. A randomised, double-blind, placebo-controlled parallel-group trial. We assigned pregnant women, from 27 weeks gestation to birth, and then their infants, from birth to six months, to placebo or one of two dosages of daily oral vitamin D. Woman/infant pairs were randomised to: placebo/placebo, 1000IU/400IU, or 2000IU/800IU. When the children were 18 months old we measured specific serum IgE antibodies and identified acute primary care visits described by the doctor to be due to a cold, otitis media, an upper respiratory infection, croup, asthma, bronchitis, bronchiolitis, a wheezy lower respiratory infection or fever and cough. Specific IgE was measured on 185/260 (71%) enrolled children. The proportion of children sensitised differed by study group for four mite antigens: Dermatophagoides farinae (Der-f1, Der-f2) and Dermatophagoides pteronyssinus (Der-p1, Der-p2). With results presented for placebo, lower-dose, and higher-dose vitamin D, respectively (all P<0·05): Der-f1 (18%, 10%, 2%), Der-f2 (14%, 3%, 2%), Der-p1 (19%, 14%, 3%), and Der-p2 (12%, 2%, 3%). There were study group differences in the proportion of children with primary care visits described by the doctor as being for asthma (11%, 0%, 4%, P=0·002), but not for the other respiratory diagnoses. Vitamin D supplementation during pregnancy and infancy reduces the proportion of children sensitised to mites at age 18 months. Preliminary data indicate a possible effect on primary care visits where asthma is diagnosed. This article is protected by copyright. All rights reserved.