To examine the use of vitamin D supplements during infancy among the participants in an international infant feeding trial.

Longitudinal study.

Information about vitamin D supplementation was collected through a validated FFQ at the age of 2 weeks and monthly between the ages of 1 month and 6 months.

Infants (n 2159) with a biological family member affected by type 1 diabetes and with increased human leucocyte antigen-conferred susceptibility to type 1 diabetes from twelve European countries, the USA, Canada and Australia.

Daily use of vitamin D supplements was common during the first 6 months of life in Northern and Central Europe (>80 % of the infants), with somewhat lower rates observed in Southern Europe (>60 %). In Canada, vitamin D supplementation was more common among exclusively breast-fed than other infants (e.g. 71 % v. 44 % at 6 months of age). Less than 2 % of infants in the USA and Australia received any vitamin D supplementation. Higher gestational age, older maternal age and longer maternal education were study-wide associated with greater use of vitamin D supplements.

Most of the infants received vitamin D supplements during the first 6 months of life in the European countries, whereas in Canada only half and in the USA and Australia very few were given supplementation.

Congenital cardiac disease is the most common malformation, and a substantial source of mortality and morbidity in children and young adults. A role for genetic factors is recognised for these malformations, but overall few predisposing loci have been identified. Here we report the rationale, design, and first results of a multi-institutional congenital cardiac disease cohort, assembled mainly from the French-Canadian population of the province of Quebec and centred on families with multiple affected members afflicted by cardiac malformations.

Families were recruited into the study, phenotyped and sampled for DNA in cardiology clinics over the first 3 years of enrolment. We performed segregation analysis and linkage simulations in the subgroup of families with left ventricular outflow tract obstruction (LVOTO).

A total of 1603 participants from 300 families were recruited, with 169 out of 300 (56.3%) families having more than one affected member. For the LVOTO group, we estimate heritability to be 0.46–0.52 in our cohort. Simulation analysis demonstrated sufficient power to carry out linkage analyses, with an expected mean log-of-odds (LOD) score of 3.8 in 67 pedigrees with LVOTO.

We show feasibility and usefulness of a population-based biobank for genetic investigations into the causes of congenital cardiac disease. Heritability of LVOTO is high and could be accounted for by multiple loci. This platform is ideally suited for multiple analysis approaches, including linkage analysis and novel gene sequencing approaches, and will allow to establish segregation of risk alleles at family and population levels.